add db functions for last checkpoint

Fix run time
Merge branch 'develop' of github.com:prysmaticlabs/prysm into kiln
2026-01-10 13:58:09 -05:00 · 2022-03-11 16:35:21 +05:30 · 2022-03-10 14:01:18 -08:00 · 2022-03-10 13:53:01 -08:00 · 2022-03-10 14:25:26 -06:00 · 2022-03-10 11:09:17 -08:00
2037 changed files with 107401 additions and 46764 deletions
--- a/.bazelrc
+++ b/.bazelrc
@@ -36,6 +36,9 @@ run --define blst_disabled=false
 build:blst_disabled --define blst_disabled=true
 build:blst_disabled --define gotags=blst_disabled

+build:minimal --//proto:network=minimal
+build:minimal --@io_bazel_rules_go//go/config:tags=minimal
+
 # Release flags
 build:release --compilation_mode=opt
 build:release --config=llvm
@@ -59,20 +62,7 @@ build:llvm-asan --config=llvm
 build:llvm-asan --config=asan
 build:llvm-asan --linkopt -fuse-ld=ld.lld

-build:fuzz --define=gotags=libfuzzer
-build:fuzz --config=llvm-asan
-build:fuzz --copt=-fsanitize=fuzzer-no-link
-build:fuzz --linkopt=-fsanitize=fuzzer
-build:fuzz --copt=-fno-omit-frame-pointer
-build:fuzz --define=FUZZING_ENGINE=libfuzzer
-build:fuzz --copt=-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
-build:fuzz --linkopt -Wl,--no-as-needed
-build:fuzz --define=gc_goopts=-d=libfuzzer,checkptr
-build:fuzz --run_under=//tools:fuzz_wrapper
-build:fuzz --compilation_mode=opt
-build:fuzz --define=blst_disabled=true
-
-test:fuzz --local_test_jobs="HOST_CPUS*.5"
+build:fuzz --@io_bazel_rules_go//go/config:tags=fuzz

 # Build binary with cgo symbolizer for debugging / profiling.
 build:cgo_symbolizer --config=llvm
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-3.7.0
+4.2.2
--- a/.buildkite-bazelrc
+++ b/.buildkite-bazelrc
@@ -10,7 +10,7 @@

 # Prysm specific remote-cache properties.
 #build:remote-cache --disk_cache=
-build:remote-cache --remote_download_minimal
+build:remote-cache --remote_download_toplevel
 build:remote-cache --remote_cache=grpc://bazel-remote-cache:9092
 build:remote-cache --experimental_remote_downloader=grpc://bazel-remote-cache:9092
 build:remote-cache --remote_local_fallback
@@ -34,16 +34,13 @@ build --sandbox_tmpfs_path=/tmp
 build --verbose_failures
 build --announce_rc
 build --show_progress_rate_limit=5
-build --curses=yes --color=no
+build --curses=no --color=no
 build --keep_going
 build --test_output=errors
 build --flaky_test_attempts=5
 # Disabled race detection due to unstable test results under constrained environment build kite
 # build --features=race

-# Disable flaky test detection for fuzzing.
-test:fuzz --flaky_test_attempts=1
-
 # Better caching
 build:nostamp --nostamp
-build:nostamp --workspace_status_command=./hack/workspace_status_ci.sh
+build:nostamp --workspace_status_command=./hack/workspace_status_ci.sh
--- a/.github/CODEOWNERS
+++ b/.github/CODEOWNERS
@@ -6,3 +6,11 @@

 # Anyone on prylabs team can approve dependency updates.
 deps.bzl @prysmaticlabs/core-team
+
+# Radek and Nishant are responsible for changes that can affect the native state feature.
+# See https://www.notion.so/prysmaticlabs/Native-Beacon-State-Redesign-6cc9744b4ec1439bb34fa829b36a35c1
+/beacon-chain/state/fieldtrie/ @rkapka @nisdas
+/beacon-chain/state/v1/ @rkapka @nisdas
+/beacon-chain/state/v2/ @rkapka @nisdas
+/beacon-chain/state/v3/ @rkapka @nisdas
+/beacon-chain/state/state-native/ @rkapka @nisdas
--- a/.github/workflows/go.yml
+++ b/.github/workflows/go.yml
@@ -24,7 +24,7 @@ jobs:
        uses: ./.github/actions/gofmt
        with:
          path: ./
-      
+
      - name: GoImports checker
        id: goimports
        uses: Jerome1337/goimports-action@v1.0.2
@@ -34,7 +34,13 @@ jobs:
      - name: Gosec security scanner
        uses: securego/gosec@master
        with:
-          args: '-exclude-dir=crypto/bls/herumi ./...'
+          args: '-exclude=G307 -exclude-dir=crypto/bls/herumi ./...'
+
+      - name: Golangci-lint
+        uses: golangci/golangci-lint-action@v2
+        with:
+          args: --print-issued-lines --sort-results --no-config --timeout=10m --disable-all -E deadcode  -E errcheck -E gosimple --skip-files=validator/web/site_data.go --skip-dirs=proto
+
  build:
    name: Build
    runs-on: ubuntu-latest
--- a/.gitignore
+++ b/.gitignore
@@ -30,9 +30,5 @@ password.txt
 # Dist files
 dist

-# libfuzzer
-oom-*
-crash-*
-
 # deepsource cli
 bin
--- a/.well-known/security.txt
+++ b/.well-known/security.txt
@@ -5,21 +5,22 @@ Contact: mailto:security@prysmaticlabs.com
 Encryption: openpgp4fpr:0AE0051D647BA3C1A917AF4072E33E4DF1A5036E
 Encryption: openpgp4fpr:CD08DE68C60B82D3EE2A3F7D95452A701810FEDB
 Encryption: openpgp4fpr:317D6E91058F8F3C2303BA7756313E44581297A6
+Encryption: openpgp4fpr:79C59A585E3FD3AFFA00F5C22940A6479DA7C9EC
 Preferred-Languages: en
 Canonical: https://github.com/prysmaticlabs/prysm/tree/master/.well-known/security.txt
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+k/znkv89dduhL9CKDvZvnI+DICwsTrf//4KJ8PM/qaPAJa4GvtiUU/eS/jKBivtv
+OP5dZQtX6KPc9ewqqZgn622uHSezoBidgeTkdZsJ6tw2eIu0lsY=
+=V7L0
 -----END PGP SIGNATURE-----
--- a/BUILD.bazel
+++ b/BUILD.bazel
@@ -86,50 +86,51 @@ nogo(
    config = "nogo_config.json",
    visibility = ["//visibility:public"],
    deps = [
-        "@org_golang_x_tools//go/analysis/passes/unsafeptr:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/unreachable:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/unmarshal:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/tests:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/structtag:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/stdmethods:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/shift:go_tool_library",
-        # "@org_golang_x_tools//go/analysis/passes/shadow:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/printf:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/pkgfact:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/nilness:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/nilfunc:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/loopclosure:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/httpresponse:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/findcall:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/deepequalerrors:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/ctrlflow:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/copylock:go_tool_library",
-        #  "@org_golang_x_tools//go/analysis/passes/cgocall:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/buildtag:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/buildssa:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/bools:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/atomicalign:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/atomic:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/assign:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/inspect:go_tool_library",
-        "@org_golang_x_tools//go/analysis/passes/asmdecl:go_tool_library",
-        "//tools/analyzers/maligned:go_tool_library",
-        "//tools/analyzers/cryptorand:go_tool_library",
-        "//tools/analyzers/errcheck:go_tool_library",
-        "//tools/analyzers/featureconfig:go_tool_library",
-        "//tools/analyzers/comparesame:go_tool_library",
-        "//tools/analyzers/shadowpredecl:go_tool_library",
-        "//tools/analyzers/nop:go_tool_library",
-        "//tools/analyzers/slicedirect:go_tool_library",
-        "//tools/analyzers/interfacechecker:go_tool_library",
-        "//tools/analyzers/ineffassign:go_tool_library",
-        "//tools/analyzers/properpermissions:go_tool_library",
+        "@org_golang_x_tools//go/analysis/passes/unsafeptr:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/unreachable:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/unmarshal:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/tests:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/structtag:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/stdmethods:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/shift:go_default_library",
+        # "@org_golang_x_tools//go/analysis/passes/shadow:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/printf:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/pkgfact:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/nilness:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/nilfunc:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/loopclosure:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/httpresponse:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/findcall:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/deepequalerrors:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/ctrlflow:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/copylock:go_default_library",
+        #  "@org_golang_x_tools//go/analysis/passes/cgocall:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/buildtag:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/buildssa:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/bools:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/atomicalign:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/atomic:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/assign:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/inspect:go_default_library",
+        "@org_golang_x_tools//go/analysis/passes/asmdecl:go_default_library",
+        "//tools/analyzers/maligned:go_default_library",
+        "//tools/analyzers/cryptorand:go_default_library",
+        "//tools/analyzers/errcheck:go_default_library",
+        "//tools/analyzers/featureconfig:go_default_library",
+        "//tools/analyzers/comparesame:go_default_library",
+        "//tools/analyzers/shadowpredecl:go_default_library",
+        "//tools/analyzers/nop:go_default_library",
+        "//tools/analyzers/slicedirect:go_default_library",
+        "//tools/analyzers/interfacechecker:go_default_library",
+        "//tools/analyzers/ineffassign:go_default_library",
+        "//tools/analyzers/properpermissions:go_default_library",
+        "//tools/analyzers/recursivelock:go_default_library",
    ] + select({
        # nogo checks that fail with coverage enabled.
        ":coverage_enabled": [],
        "//conditions:default": [
-            "@org_golang_x_tools//go/analysis/passes/lostcancel:go_tool_library",
-            "@org_golang_x_tools//go/analysis/passes/composite:go_tool_library",
+            "@org_golang_x_tools//go/analysis/passes/lostcancel:go_default_library",
+            "@org_golang_x_tools//go/analysis/passes/composite:go_default_library",
        ],
    }),
 )
@@ -144,21 +145,6 @@ common_files = {
    "//:README.md": "README.md",
 }

-toolchain(
-    name = "built_cmake_toolchain",
-    toolchain = "@rules_foreign_cc//tools/build_defs/native_tools:built_cmake",
-    toolchain_type = "@rules_foreign_cc//tools/build_defs:cmake_toolchain",
-)
-
-string_setting(
-    name = "gotags",
-    build_setting_default = "",
-    values = [
-        "",
-        "libfuzzer",
-    ],
-)
-
 sh_binary(
    name = "prysm_sh",
    srcs = ["prysm.sh"],
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -190,7 +190,7 @@ Anyone can become a part-time contributor and help out on implementing Ethereum

 Core contributors are remote contractors of Prysmatic Labs, LLC. and are considered critical team members of our organization. Core devs have all of the responsibilities of part-time contributors plus the majority of the following:

-   Stay up to date on the latest beacon chain sepcification
+-   Stay up to date on the latest beacon chain specification
 -   Monitor github issues and PR’s to make sure owner, labels, descriptions are correct
 -   Formulate independent ideas, suggest new work to do, point out improvements to existing approaches
 -   Participate in code review, ensure code quality is excellent, and have ensure high code coverage
--- a/README.md
+++ b/README.md
@@ -2,7 +2,7 @@

 [![Build status](https://badge.buildkite.com/b555891daf3614bae4284dcf365b2340cefc0089839526f096.svg?branch=master)](https://buildkite.com/prysmatic-labs/prysm)
 [![Go Report Card](https://goreportcard.com/badge/github.com/prysmaticlabs/prysm)](https://goreportcard.com/report/github.com/prysmaticlabs/prysm)
-[![ETH2.0_Spec_Version 1.0.0](https://img.shields.io/badge/ETH2.0%20Spec%20Version-v1.0.0-blue.svg)](https://github.com/ethereum/consensus-specs/tree/v1.0.0)
+[![Consensus_Spec_Version 1.1.8](https://img.shields.io/badge/Consensus%20Spec%20Version-v1.1.8-blue.svg)](https://github.com/ethereum/consensus-specs/tree/v1.1.8)
 [![Discord](https://user-images.githubusercontent.com/7288322/34471967-1df7808a-efbb-11e7-9088-ed0b04151291.png)](https://discord.gg/CTYGPUJ)

 This is the core repository for Prysm, a [Golang](https://golang.org/) implementation of the [Ethereum Consensus](https://ethereum.org/en/eth2/) specification, developed by [Prysmatic Labs](https://prysmaticlabs.com). See the [Changelog](https://github.com/prysmaticlabs/prysm/releases) for details of the latest releases and upcoming breaking changes.
--- a/91
+++ b/91
@@ -60,10 +60,10 @@ bazel_skylib_workspace()

 http_archive(
    name = "bazel_gazelle",
-    sha256 = "62ca106be173579c0a167deb23358fdfe71ffa1e4cfdddf5582af26520f1c66f",
+    sha256 = "de69a09dc70417580aabf20a28619bb3ef60d038470c7cf8442fafcf627c21cb",
    urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/bazel-gazelle/releases/download/v0.23.0/bazel-gazelle-v0.23.0.tar.gz",
-        "https://github.com/bazelbuild/bazel-gazelle/releases/download/v0.23.0/bazel-gazelle-v0.23.0.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/bazel-gazelle/releases/download/v0.24.0/bazel-gazelle-v0.24.0.tar.gz",
+        "https://github.com/bazelbuild/bazel-gazelle/releases/download/v0.24.0/bazel-gazelle-v0.24.0.tar.gz",
    ],
 )

@@ -76,25 +76,22 @@ http_archive(

 http_archive(
    name = "io_bazel_rules_docker",
-    sha256 = "59d5b42ac315e7eadffa944e86e90c2990110a1c8075f1cd145f487e999d22b3",
-    strip_prefix = "rules_docker-0.17.0",
-    urls = ["https://github.com/bazelbuild/rules_docker/releases/download/v0.17.0/rules_docker-v0.17.0.tar.gz"],
+    sha256 = "1f4e59843b61981a96835dc4ac377ad4da9f8c334ebe5e0bb3f58f80c09735f4",
+    strip_prefix = "rules_docker-0.19.0",
+    urls = ["https://github.com/bazelbuild/rules_docker/releases/download/v0.19.0/rules_docker-v0.19.0.tar.gz"],
 )

 http_archive(
    name = "io_bazel_rules_go",
    patch_args = ["-p1"],
    patches = [
-        # Required until https://github.com/bazelbuild/rules_go/pull/2450 merges otherwise nilness
-        # nogo check fails for certain third_party dependencies.
-        "//third_party:io_bazel_rules_go.patch",
        # Expose internals of go_test for custom build transitions.
        "//third_party:io_bazel_rules_go_test.patch",
    ],
-    sha256 = "7c10271940c6bce577d51a075ae77728964db285dac0a46614a7934dc34303e6",
+    sha256 = "2b1641428dff9018f9e85c0384f03ec6c10660d935b750e3fa1492a281a53b0f",
    urls = [
-        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.26.0/rules_go-v0.26.0.tar.gz",
-        "https://github.com/bazelbuild/rules_go/releases/download/v0.26.0/rules_go-v0.26.0.tar.gz",
+        "https://mirror.bazel.build/github.com/bazelbuild/rules_go/releases/download/v0.29.0/rules_go-v0.29.0.zip",
+        "https://github.com/bazelbuild/rules_go/releases/download/v0.29.0/rules_go-v0.29.0.zip",
    ],
 )

@@ -139,6 +136,34 @@ load(
    "container_pull",
 )

+container_pull(
+    name = "cc_image_base",
+    digest = "sha256:2c4bb6b7236db0a55ec54ba8845e4031f5db2be957ac61867872bf42e56c4deb",
+    registry = "gcr.io",
+    repository = "distroless/cc",
+)
+
+container_pull(
+    name = "cc_debug_image_base",
+    digest = "sha256:3680c61e81f68fc00bfb5e1ec65e8e678aaafa7c5f056bc2681c29527ebbb30c",
+    registry = "gcr.io",
+    repository = "distroless/cc",
+)
+
+container_pull(
+    name = "go_image_base",
+    digest = "sha256:ba7a315f86771332e76fa9c3d423ecfdbb8265879c6f1c264d6fff7d4fa460a4",
+    registry = "gcr.io",
+    repository = "distroless/base",
+)
+
+container_pull(
+    name = "go_debug_image_base",
+    digest = "sha256:efd8711717d9e9b5d0dbb20ea10876dab0609c923bc05321b912f9239090ca80",
+    registry = "gcr.io",
+    repository = "distroless/base",
+)
+
 container_pull(
    name = "alpine_cc_linux_amd64",
    digest = "sha256:752aa0c9a88461ffc50c5267bb7497ef03a303e38b2c8f7f2ded9bebe5f1f00e",
@@ -158,7 +183,7 @@ load("@io_bazel_rules_go//go:deps.bzl", "go_register_toolchains", "go_rules_depe
 go_rules_dependencies()

 go_register_toolchains(
-    go_version = "1.16.4",
+    go_version = "1.17.6",
    nogo = "@//:nogo",
 )

@@ -194,10 +219,10 @@ filegroup(
 )
    """,
    sha256 = "91434d5fd5e1c6eb7b0174fed2afe25e09bddf00e1e4c431db931b2cee4e7773",
-    url = "https://github.com/eth2-clients/slashing-protection-interchange-tests/archive/b8413ca42dc92308019d0d4db52c87e9e125c4e9.tar.gz",
+    url = "https://github.com/eth-clients/slashing-protection-interchange-tests/archive/b8413ca42dc92308019d0d4db52c87e9e125c4e9.tar.gz",
 )

-consensus_spec_version = "v1.1.0-beta.4"
+consensus_spec_version = "v1.1.9"

 bls_test_version = "v0.1.1"

@@ -213,7 +238,7 @@ filegroup(
    visibility = ["//visibility:public"],
 )
    """,
-    sha256 = "d2d501453cf29777896a5f9ae52e93921f34330e57fcc5b55e4982d4795236b9",
+    sha256 = "207d9c326ba4fa1f34bab7b6169201c32f2611755db030909a3405873445e0ba",
    url = "https://github.com/ethereum/consensus-spec-tests/releases/download/%s/general.tar.gz" % consensus_spec_version,
 )

@@ -229,7 +254,7 @@ filegroup(
    visibility = ["//visibility:public"],
 )
    """,
-    sha256 = "b152f1f03a4fdacd1882fe867bdfbd5067e74ed3c532bd01d81e7adf6cc3737a",
+    sha256 = "a3995b39f412db236b2f1db909f288218da53cb53b9923b71dda9d144d68f40a",
    url = "https://github.com/ethereum/consensus-spec-tests/releases/download/%s/minimal.tar.gz" % consensus_spec_version,
 )

@@ -245,7 +270,7 @@ filegroup(
    visibility = ["//visibility:public"],
 )
    """,
-    sha256 = "6046f89c679a9ffda217dee6f021eb7c4fe91aad6ff940fae4d2cf894cc61cbb",
+    sha256 = "76cea7a4c8e32d458ad456b54bfbb30bc772481a91954a4cd97e229aa3023b1d",
    url = "https://github.com/ethereum/consensus-spec-tests/releases/download/%s/mainnet.tar.gz" % consensus_spec_version,
 )

@@ -260,7 +285,7 @@ filegroup(
    visibility = ["//visibility:public"],
 )
    """,
-    sha256 = "26a0a2c3022a3c5354f3204c7e441580df2e585dbde22a43a1d43f885b3a221c",
+    sha256 = "0fc429684775f943250dce1f9c485ac25e26c6395d7f585c8d1317becec2ace7",
    strip_prefix = "consensus-specs-" + consensus_spec_version[1:],
    url = "https://github.com/ethereum/consensus-specs/archive/refs/tags/%s.tar.gz" % consensus_spec_version,
 )
@@ -291,9 +316,9 @@ filegroup(
    visibility = ["//visibility:public"],
 )
    """,
-    sha256 = "9dc47bf6b14aed7fac8833e35ab83a69131b43fa5789b3256bf1ac3d4861aeb8",
-    strip_prefix = "eth2-networks-7fa1b868985ee24aad65567f9250cf7fa86f97b1",
-    url = "https://github.com/eth2-clients/eth2-networks/archive/7fa1b868985ee24aad65567f9250cf7fa86f97b1.tar.gz",
+    sha256 = "4e8a18b21d056c4032605621b1a6632198eabab57cb90c61e273f344c287f1b2",
+    strip_prefix = "eth2-networks-791a5369c5981e829698b17fbcdcdacbdaba97c8",
+    url = "https://github.com/eth-clients/eth2-networks/archive/791a5369c5981e829698b17fbcdcdacbdaba97c8.tar.gz",
 )

 http_archive(
@@ -313,16 +338,6 @@ git_repository(
 # Group the sources of the library so that CMake rule have access to it
 all_content = """filegroup(name = "all", srcs = glob(["**"]), visibility = ["//visibility:public"])"""

-http_archive(
-    name = "sigp_beacon_fuzz_corpora",
-    build_file = "//third_party:beacon-fuzz/corpora.BUILD",
-    sha256 = "42993d0901a316afda45b4ba6d53c7c21f30c551dcec290a4ca131c24453d1ef",
-    strip_prefix = "beacon-fuzz-corpora-bac24ad78d45cc3664c0172241feac969c1ac29b",
-    urls = [
-        "https://github.com/sigp/beacon-fuzz-corpora/archive/bac24ad78d45cc3664c0172241feac969c1ac29b.tar.gz",
-    ],
-)
-
 # External dependencies

 http_archive(
@@ -334,9 +349,9 @@ filegroup(
    visibility = ["//visibility:public"],
 )
 """,
-    sha256 = "54ce527b83d092da01127f2e3816f4d5cfbab69354caba8537f1ea55889b6d7c",
+    sha256 = "4797a7e594a5b1f4c1c8080701613f3ee451b01ec0861499ea7d9b60877a6b23",
    urls = [
-        "https://github.com/prysmaticlabs/prysm-web-ui/releases/download/v1.0.0-beta.4/prysm-web-ui.tar.gz",
+        "https://github.com/prysmaticlabs/prysm-web-ui/releases/download/v1.0.3/prysm-web-ui.tar.gz",
    ],
 )

@@ -349,6 +364,10 @@ load("@prysm//third_party/herumi:herumi.bzl", "bls_dependencies")

 bls_dependencies()

+load("@prysm//testing/endtoend:deps.bzl", "e2e_deps")
+
+e2e_deps()
+
 load(
    "@io_bazel_rules_docker//go:image.bzl",
    _go_image_repos = "repositories",
@@ -367,10 +386,6 @@ load(

 _cc_image_repos()

-load("@com_github_ethereum_go_ethereum//:deps.bzl", "geth_dependencies")
-
-geth_dependencies()
-
 load("@io_bazel_rules_go//extras:embed_data_deps.bzl", "go_embed_data_dependencies")

 go_embed_data_dependencies()
--- a/api/gateway/BUILD.bazel
+++ b/api/gateway/BUILD.bazel
@@ -3,12 +3,9 @@ load("@prysm//tools/go:def.bzl", "go_library", "go_test")
 go_library(
    name = "go_default_library",
    srcs = [
-        "api_middleware.go",
-        "api_middleware_processing.go",
-        "api_middleware_structs.go",
        "gateway.go",
        "log.go",
-        "param_handling.go",
+        "options.go",
    ],
    importpath = "github.com/prysmaticlabs/prysm/api/gateway",
    visibility = [
@@ -16,16 +13,13 @@ go_library(
        "//validator:__subpackages__",
    ],
    deps = [
-        "//api/grpc:go_default_library",
+        "//api/gateway/apimiddleware:go_default_library",
        "//runtime:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "@com_github_ethereum_go_ethereum//common/hexutil:go_default_library",
        "@com_github_gorilla_mux//:go_default_library",
        "@com_github_grpc_ecosystem_grpc_gateway_v2//runtime:go_default_library",
        "@com_github_pkg_errors//:go_default_library",
        "@com_github_rs_cors//:go_default_library",
        "@com_github_sirupsen_logrus//:go_default_library",
-        "@com_github_wealdtech_go_bytesutil//:go_default_library",
        "@org_golang_google_grpc//:go_default_library",
        "@org_golang_google_grpc//connectivity:go_default_library",
        "@org_golang_google_grpc//credentials:go_default_library",
@@ -34,17 +28,13 @@ go_library(

 go_test(
    name = "go_default_test",
-    srcs = [
-        "api_middleware_processing_test.go",
-        "gateway_test.go",
-        "param_handling_test.go",
-    ],
+    srcs = ["gateway_test.go"],
    embed = [":go_default_library"],
    deps = [
-        "//api/grpc:go_default_library",
+        "//api/gateway/apimiddleware:go_default_library",
        "//cmd/beacon-chain/flags:go_default_library",
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
        "@com_github_gorilla_mux//:go_default_library",
        "@com_github_sirupsen_logrus//hooks/test:go_default_library",
        "@com_github_urfave_cli_v2//:go_default_library",
--- a/api/gateway/api_middleware.go
+++ b/api/gateway/api_middleware.go
@@ -1,217 +0,0 @@
-package gateway
-
-import (
-	"net/http"
-	"reflect"
-
-	"github.com/gorilla/mux"
-)
-
-// ApiProxyMiddleware is a proxy between an Ethereum consensus API HTTP client and grpc-gateway.
-// The purpose of the proxy is to handle HTTP requests and gRPC responses in such a way that:
-//   - Ethereum consensus API requests can be handled by grpc-gateway correctly
-//   - gRPC responses can be returned as spec-compliant Ethereum consensus API responses
-type ApiProxyMiddleware struct {
-	GatewayAddress  string
-	ProxyAddress    string
-	EndpointCreator EndpointFactory
-	router          *mux.Router
-}
-
-// EndpointFactory is responsible for creating new instances of Endpoint values.
-type EndpointFactory interface {
-	Create(path string) (*Endpoint, error)
-	Paths() []string
-	IsNil() bool
-}
-
-// Endpoint is a representation of an API HTTP endpoint that should be proxied by the middleware.
-type Endpoint struct {
-	Path               string          // The path of the HTTP endpoint.
-	PostRequest        interface{}     // The struct corresponding to the JSON structure used in a POST request.
-	PostResponse       interface{}     // The struct corresponding to the JSON structure used in a POST response.
-	RequestURLLiterals []string        // Names of URL parameters that should not be base64-encoded.
-	RequestQueryParams []QueryParam    // Query parameters of the request.
-	GetResponse        interface{}     // The struct corresponding to the JSON structure used in a GET response.
-	Err                ErrorJson       // The struct corresponding to the error that should be returned in case of a request failure.
-	Hooks              HookCollection  // A collection of functions that can be invoked at various stages of the request/response cycle.
-	CustomHandlers     []CustomHandler // Functions that will be executed instead of the default request/response behaviour.
-}
-
-// DefaultEndpoint returns an Endpoint with default configuration, e.g. DefaultErrorJson for error handling.
-func DefaultEndpoint() Endpoint {
-	return Endpoint{
-		Err: &DefaultErrorJson{},
-	}
-}
-
-// QueryParam represents a single query parameter's metadata.
-type QueryParam struct {
-	Name string
-	Hex  bool
-	Enum bool
-}
-
-// Hook is a function that can be invoked at various stages of the request/response cycle, leading to custom behaviour for a specific endpoint.
-type Hook = func(endpoint Endpoint, w http.ResponseWriter, req *http.Request) ErrorJson
-
-// CustomHandler is a function that can be invoked at the very beginning of the request,
-// essentially replacing the whole default request/response logic with custom logic for a specific endpoint.
-type CustomHandler = func(m *ApiProxyMiddleware, endpoint Endpoint, w http.ResponseWriter, req *http.Request) (handled bool)
-
-// HookCollection contains hooks that can be used to amend the default request/response cycle with custom logic for a specific endpoint.
-type HookCollection struct {
-	OnPreDeserializeRequestBodyIntoContainer      []Hook
-	OnPostDeserializeRequestBodyIntoContainer     []Hook
-	OnPreDeserializeGrpcResponseBodyIntoContainer []func([]byte, interface{}) (bool, ErrorJson)
-	OnPreSerializeMiddlewareResponseIntoJson      []func(interface{}) (bool, []byte, ErrorJson)
-}
-
-// fieldProcessor applies the processing function f to a value when the tag is present on the field.
-type fieldProcessor struct {
-	tag string
-	f   func(value reflect.Value) error
-}
-
-// Run starts the proxy, registering all proxy endpoints on ApiProxyMiddleware.ProxyAddress.
-func (m *ApiProxyMiddleware) Run() error {
-	m.router = mux.NewRouter()
-
-	for _, path := range m.EndpointCreator.Paths() {
-		m.handleApiPath(path, m.EndpointCreator)
-	}
-
-	return http.ListenAndServe(m.ProxyAddress, m.router)
-}
-
-func (m *ApiProxyMiddleware) handleApiPath(path string, endpointFactory EndpointFactory) {
-	m.router.HandleFunc(path, func(w http.ResponseWriter, req *http.Request) {
-		endpoint, err := endpointFactory.Create(path)
-		if err != nil {
-			errJson := InternalServerErrorWithMessage(err, "could not create endpoint")
-			WriteError(w, errJson, nil)
-		}
-
-		for _, handler := range endpoint.CustomHandlers {
-			if handler(m, *endpoint, w, req) {
-				return
-			}
-		}
-
-		if req.Method == "POST" {
-			for _, hook := range endpoint.Hooks.OnPreDeserializeRequestBodyIntoContainer {
-				if errJson := hook(*endpoint, w, req); errJson != nil {
-					WriteError(w, errJson, nil)
-					return
-				}
-			}
-
-			if errJson := DeserializeRequestBodyIntoContainer(req.Body, endpoint.PostRequest); errJson != nil {
-				WriteError(w, errJson, nil)
-				return
-			}
-			for _, hook := range endpoint.Hooks.OnPostDeserializeRequestBodyIntoContainer {
-				if errJson := hook(*endpoint, w, req); errJson != nil {
-					WriteError(w, errJson, nil)
-					return
-				}
-			}
-
-			if errJson := ProcessRequestContainerFields(endpoint.PostRequest); errJson != nil {
-				WriteError(w, errJson, nil)
-				return
-			}
-			if errJson := SetRequestBodyToRequestContainer(endpoint.PostRequest, req); errJson != nil {
-				WriteError(w, errJson, nil)
-				return
-			}
-		}
-
-		if errJson := m.PrepareRequestForProxying(*endpoint, req); errJson != nil {
-			WriteError(w, errJson, nil)
-			return
-		}
-		grpcResponse, errJson := ProxyRequest(req)
-		if errJson != nil {
-			WriteError(w, errJson, nil)
-			return
-		}
-		grpcResponseBody, errJson := ReadGrpcResponseBody(grpcResponse.Body)
-		if errJson != nil {
-			WriteError(w, errJson, nil)
-			return
-		}
-
-		var responseJson []byte
-		if !GrpcResponseIsEmpty(grpcResponseBody) {
-			if errJson := DeserializeGrpcResponseBodyIntoErrorJson(endpoint.Err, grpcResponseBody); errJson != nil {
-				WriteError(w, errJson, nil)
-				return
-			}
-			if endpoint.Err.Msg() != "" {
-				HandleGrpcResponseError(endpoint.Err, grpcResponse, w)
-				return
-			}
-			var response interface{}
-			if req.Method == "GET" {
-				response = endpoint.GetResponse
-			} else {
-				response = endpoint.PostResponse
-			}
-
-			runDefault := true
-			for _, hook := range endpoint.Hooks.OnPreDeserializeGrpcResponseBodyIntoContainer {
-				ok, errJson := hook(grpcResponseBody, response)
-				if errJson != nil {
-					WriteError(w, errJson, nil)
-					return
-				}
-				if ok {
-					runDefault = false
-					break
-				}
-			}
-			if runDefault {
-				if errJson := DeserializeGrpcResponseBodyIntoContainer(grpcResponseBody, response); errJson != nil {
-					WriteError(w, errJson, nil)
-					return
-				}
-			}
-
-			if errJson := ProcessMiddlewareResponseFields(response); errJson != nil {
-				WriteError(w, errJson, nil)
-				return
-			}
-
-			var ok bool
-			runDefault = true
-			for _, hook := range endpoint.Hooks.OnPreSerializeMiddlewareResponseIntoJson {
-				ok, responseJson, errJson = hook(response)
-				if errJson != nil {
-					WriteError(w, errJson, nil)
-					return
-				}
-				if ok {
-					runDefault = false
-					break
-				}
-			}
-			if runDefault {
-				responseJson, errJson = SerializeMiddlewareResponseIntoJson(response)
-				if errJson != nil {
-					WriteError(w, errJson, nil)
-					return
-				}
-			}
-		}
-
-		if errJson := WriteMiddlewareResponseHeadersAndBody(grpcResponse, responseJson, w); errJson != nil {
-			WriteError(w, errJson, nil)
-			return
-		}
-		if errJson := Cleanup(grpcResponse.Body); errJson != nil {
-			WriteError(w, errJson, nil)
-			return
-		}
-	})
-}
--- a/api/gateway/apimiddleware/BUILD.bazel
+++ b/api/gateway/apimiddleware/BUILD.bazel
@@ -0,0 +1,40 @@
+load("@prysm//tools/go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "api_middleware.go",
+        "log.go",
+        "param_handling.go",
+        "process_field.go",
+        "process_request.go",
+        "structs.go",
+    ],
+    importpath = "github.com/prysmaticlabs/prysm/api/gateway/apimiddleware",
+    visibility = ["//visibility:public"],
+    deps = [
+        "//api/grpc:go_default_library",
+        "//encoding/bytesutil:go_default_library",
+        "@com_github_ethereum_go_ethereum//common/hexutil:go_default_library",
+        "@com_github_gorilla_mux//:go_default_library",
+        "@com_github_pkg_errors//:go_default_library",
+        "@com_github_sirupsen_logrus//:go_default_library",
+        "@com_github_wealdtech_go_bytesutil//:go_default_library",
+    ],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = [
+        "param_handling_test.go",
+        "process_request_test.go",
+    ],
+    embed = [":go_default_library"],
+    deps = [
+        "//api/grpc:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
+        "@com_github_gorilla_mux//:go_default_library",
+        "@com_github_sirupsen_logrus//hooks/test:go_default_library",
+    ],
+)
--- a/api/gateway/apimiddleware/api_middleware.go
+++ b/api/gateway/apimiddleware/api_middleware.go
@@ -0,0 +1,265 @@
+package apimiddleware
+
+import (
+	"net/http"
+	"reflect"
+	"time"
+
+	"github.com/gorilla/mux"
+)
+
+// ApiProxyMiddleware is a proxy between an Ethereum consensus API HTTP client and grpc-gateway.
+// The purpose of the proxy is to handle HTTP requests and gRPC responses in such a way that:
+//   - Ethereum consensus API requests can be handled by grpc-gateway correctly
+//   - gRPC responses can be returned as spec-compliant Ethereum consensus API responses
+type ApiProxyMiddleware struct {
+	GatewayAddress  string
+	EndpointCreator EndpointFactory
+	Timeout         time.Duration
+	router          *mux.Router
+}
+
+// EndpointFactory is responsible for creating new instances of Endpoint values.
+type EndpointFactory interface {
+	Create(path string) (*Endpoint, error)
+	Paths() []string
+	IsNil() bool
+}
+
+// Endpoint is a representation of an API HTTP endpoint that should be proxied by the middleware.
+type Endpoint struct {
+	Path               string          // The path of the HTTP endpoint.
+	GetResponse        interface{}     // The struct corresponding to the JSON structure used in a GET response.
+	PostRequest        interface{}     // The struct corresponding to the JSON structure used in a POST request.
+	PostResponse       interface{}     // The struct corresponding to the JSON structure used in a POST response.
+	DeleteRequest      interface{}     // The struct corresponding to the JSON structure used in a DELETE request.
+	DeleteResponse     interface{}     // The struct corresponding to the JSON structure used in a DELETE response.
+	RequestURLLiterals []string        // Names of URL parameters that should not be base64-encoded.
+	RequestQueryParams []QueryParam    // Query parameters of the request.
+	Err                ErrorJson       // The struct corresponding to the error that should be returned in case of a request failure.
+	Hooks              HookCollection  // A collection of functions that can be invoked at various stages of the request/response cycle.
+	CustomHandlers     []CustomHandler // Functions that will be executed instead of the default request/response behaviour.
+}
+
+// RunDefault expresses whether the default processing logic should be carried out after running a pre hook.
+type RunDefault bool
+
+// DefaultEndpoint returns an Endpoint with default configuration, e.g. DefaultErrorJson for error handling.
+func DefaultEndpoint() Endpoint {
+	return Endpoint{
+		Err: &DefaultErrorJson{},
+	}
+}
+
+// QueryParam represents a single query parameter's metadata.
+type QueryParam struct {
+	Name string
+	Hex  bool
+	Enum bool
+}
+
+// CustomHandler is a function that can be invoked at the very beginning of the request,
+// essentially replacing the whole default request/response logic with custom logic for a specific endpoint.
+type CustomHandler = func(m *ApiProxyMiddleware, endpoint Endpoint, w http.ResponseWriter, req *http.Request) (handled bool)
+
+// HookCollection contains hooks that can be used to amend the default request/response cycle with custom logic for a specific endpoint.
+type HookCollection struct {
+	OnPreDeserializeRequestBodyIntoContainer      func(endpoint *Endpoint, w http.ResponseWriter, req *http.Request) (RunDefault, ErrorJson)
+	OnPostDeserializeRequestBodyIntoContainer     func(endpoint *Endpoint, w http.ResponseWriter, req *http.Request) ErrorJson
+	OnPreDeserializeGrpcResponseBodyIntoContainer func([]byte, interface{}) (RunDefault, ErrorJson)
+	OnPreSerializeMiddlewareResponseIntoJson      func(interface{}) (RunDefault, []byte, ErrorJson)
+}
+
+// fieldProcessor applies the processing function f to a value when the tag is present on the field.
+type fieldProcessor struct {
+	tag string
+	f   func(value reflect.Value) error
+}
+
+// Run starts the proxy, registering all proxy endpoints.
+func (m *ApiProxyMiddleware) Run(gatewayRouter *mux.Router) {
+	for _, path := range m.EndpointCreator.Paths() {
+		gatewayRouter.HandleFunc(path, m.WithMiddleware(path))
+	}
+	m.router = gatewayRouter
+}
+
+// ServeHTTP for the proxy middleware.
+func (m *ApiProxyMiddleware) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	m.router.ServeHTTP(w, req)
+}
+
+// WithMiddleware wraps the given endpoint handler with the middleware logic.
+func (m *ApiProxyMiddleware) WithMiddleware(path string) http.HandlerFunc {
+	return func(w http.ResponseWriter, req *http.Request) {
+		endpoint, err := m.EndpointCreator.Create(path)
+		if err != nil {
+			log.WithError(err).Errorf("Could not create endpoint for path: %s", path)
+			return
+		}
+
+		for _, handler := range endpoint.CustomHandlers {
+			if handler(m, *endpoint, w, req) {
+				return
+			}
+		}
+
+		if req.Method == "POST" {
+			if errJson := handlePostRequestForEndpoint(endpoint, w, req); errJson != nil {
+				WriteError(w, errJson, nil)
+				return
+			}
+		}
+
+		if req.Method == "DELETE" {
+			if errJson := handleDeleteRequestForEndpoint(endpoint, req); errJson != nil {
+				WriteError(w, errJson, nil)
+				return
+			}
+		}
+
+		if errJson := m.PrepareRequestForProxying(*endpoint, req); errJson != nil {
+			WriteError(w, errJson, nil)
+			return
+		}
+		grpcResp, errJson := m.ProxyRequest(req)
+		if errJson != nil {
+			WriteError(w, errJson, nil)
+			return
+		}
+		grpcRespBody, errJson := ReadGrpcResponseBody(grpcResp.Body)
+		if errJson != nil {
+			WriteError(w, errJson, nil)
+			return
+		}
+
+		var respJson []byte
+		if !GrpcResponseIsEmpty(grpcRespBody) {
+			respHasError, errJson := HandleGrpcResponseError(endpoint.Err, grpcResp, grpcRespBody, w)
+			if errJson != nil {
+				WriteError(w, errJson, nil)
+				return
+			}
+			if respHasError {
+				return
+			}
+
+			var resp interface{}
+			if req.Method == "GET" {
+				resp = endpoint.GetResponse
+			} else if req.Method == "DELETE" {
+				resp = endpoint.DeleteResponse
+			} else {
+				resp = endpoint.PostResponse
+			}
+			if errJson := deserializeGrpcResponseBodyIntoContainerWrapped(endpoint, grpcRespBody, resp); errJson != nil {
+				WriteError(w, errJson, nil)
+				return
+			}
+			if errJson := ProcessMiddlewareResponseFields(resp); errJson != nil {
+				WriteError(w, errJson, nil)
+				return
+			}
+
+			respJson, errJson = serializeMiddlewareResponseIntoJsonWrapped(endpoint, respJson, resp)
+			if errJson != nil {
+				WriteError(w, errJson, nil)
+				return
+			}
+		}
+
+		if errJson := WriteMiddlewareResponseHeadersAndBody(grpcResp, respJson, w); errJson != nil {
+			WriteError(w, errJson, nil)
+			return
+		}
+		if errJson := Cleanup(grpcResp.Body); errJson != nil {
+			WriteError(w, errJson, nil)
+			return
+		}
+	}
+}
+
+func handlePostRequestForEndpoint(endpoint *Endpoint, w http.ResponseWriter, req *http.Request) ErrorJson {
+	if errJson := deserializeRequestBodyIntoContainerWrapped(endpoint, req, w); errJson != nil {
+		return errJson
+	}
+	if errJson := ProcessRequestContainerFields(endpoint.PostRequest); errJson != nil {
+		return errJson
+	}
+	return SetRequestBodyToRequestContainer(endpoint.PostRequest, req)
+}
+
+func handleDeleteRequestForEndpoint(endpoint *Endpoint, req *http.Request) ErrorJson {
+	if errJson := DeserializeRequestBodyIntoContainer(req.Body, endpoint.DeleteRequest); errJson != nil {
+		return errJson
+	}
+	if errJson := ProcessRequestContainerFields(endpoint.DeleteRequest); errJson != nil {
+		return errJson
+	}
+	return SetRequestBodyToRequestContainer(endpoint.DeleteRequest, req)
+}
+
+func deserializeRequestBodyIntoContainerWrapped(endpoint *Endpoint, req *http.Request, w http.ResponseWriter) ErrorJson {
+	runDefault := true
+	if endpoint.Hooks.OnPreDeserializeRequestBodyIntoContainer != nil {
+		run, errJson := endpoint.Hooks.OnPreDeserializeRequestBodyIntoContainer(endpoint, w, req)
+		if errJson != nil {
+			return errJson
+		}
+		if !run {
+			runDefault = false
+		}
+	}
+	if runDefault {
+		if errJson := DeserializeRequestBodyIntoContainer(req.Body, endpoint.PostRequest); errJson != nil {
+			return errJson
+		}
+	}
+	if endpoint.Hooks.OnPostDeserializeRequestBodyIntoContainer != nil {
+		if errJson := endpoint.Hooks.OnPostDeserializeRequestBodyIntoContainer(endpoint, w, req); errJson != nil {
+			return errJson
+		}
+	}
+	return nil
+}
+
+func deserializeGrpcResponseBodyIntoContainerWrapped(endpoint *Endpoint, grpcResponseBody []byte, resp interface{}) ErrorJson {
+	runDefault := true
+	if endpoint.Hooks.OnPreDeserializeGrpcResponseBodyIntoContainer != nil {
+		run, errJson := endpoint.Hooks.OnPreDeserializeGrpcResponseBodyIntoContainer(grpcResponseBody, resp)
+		if errJson != nil {
+			return errJson
+		}
+		if !run {
+			runDefault = false
+		}
+	}
+	if runDefault {
+		if errJson := DeserializeGrpcResponseBodyIntoContainer(grpcResponseBody, resp); errJson != nil {
+			return errJson
+		}
+	}
+	return nil
+}
+
+func serializeMiddlewareResponseIntoJsonWrapped(endpoint *Endpoint, respJson []byte, resp interface{}) ([]byte, ErrorJson) {
+	runDefault := true
+	var errJson ErrorJson
+	if endpoint.Hooks.OnPreSerializeMiddlewareResponseIntoJson != nil {
+		var run RunDefault
+		run, respJson, errJson = endpoint.Hooks.OnPreSerializeMiddlewareResponseIntoJson(resp)
+		if errJson != nil {
+			return nil, errJson
+		}
+		if !run {
+			runDefault = false
+		}
+	}
+	if runDefault {
+		respJson, errJson = SerializeMiddlewareResponseIntoJson(resp)
+		if errJson != nil {
+			return nil, errJson
+		}
+	}
+	return respJson, nil
+}
--- a/api/gateway/apimiddleware/log.go
+++ b/api/gateway/apimiddleware/log.go
@@ -0,0 +1,5 @@
+package apimiddleware
+
+import "github.com/sirupsen/logrus"
+
+var log = logrus.WithField("prefix", "apimiddleware")
--- a/api/gateway/apimiddleware/param_handling.go
+++ b/api/gateway/apimiddleware/param_handling.go
@@ -1,4 +1,4 @@
-package gateway
+package apimiddleware

 import (
 	"encoding/base64"
@@ -7,7 +7,7 @@ import (
 	"strings"

 	"github.com/gorilla/mux"
-	butil "github.com/prysmaticlabs/prysm/shared/bytesutil"
+	butil "github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	"github.com/wealdtech/go-bytesutil"
 )

--- a/api/gateway/apimiddleware/param_handling_test.go
+++ b/api/gateway/apimiddleware/param_handling_test.go
@@ -1,4 +1,4 @@
-package gateway
+package apimiddleware

 import (
 	"bytes"
@@ -6,8 +6,8 @@ import (
 	"testing"

 	"github.com/gorilla/mux"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 func TestHandleURLParameters(t *testing.T) {
--- a/api/gateway/apimiddleware/process_field.go
+++ b/api/gateway/apimiddleware/process_field.go
@@ -0,0 +1,108 @@
+package apimiddleware
+
+import (
+	"encoding/base64"
+	"fmt"
+	"reflect"
+	"strconv"
+	"strings"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/pkg/errors"
+	"github.com/wealdtech/go-bytesutil"
+)
+
+// processField calls each processor function on any field that has the matching tag set.
+// It is a recursive function.
+func processField(s interface{}, processors []fieldProcessor) error {
+	kind := reflect.TypeOf(s).Kind()
+	if kind != reflect.Ptr && kind != reflect.Slice && kind != reflect.Array {
+		return fmt.Errorf("processing fields of kind '%v' is unsupported", kind)
+	}
+
+	t := reflect.TypeOf(s).Elem()
+	v := reflect.Indirect(reflect.ValueOf(s))
+
+	for i := 0; i < t.NumField(); i++ {
+		switch v.Field(i).Kind() {
+		case reflect.Slice:
+			sliceElem := t.Field(i).Type.Elem()
+			kind := sliceElem.Kind()
+			// Recursively process slices to struct pointers.
+			if kind == reflect.Ptr && sliceElem.Elem().Kind() == reflect.Struct {
+				for j := 0; j < v.Field(i).Len(); j++ {
+					if err := processField(v.Field(i).Index(j).Interface(), processors); err != nil {
+						return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
+					}
+				}
+			}
+			// Process each string in string slices.
+			if kind == reflect.String {
+				for _, proc := range processors {
+					_, hasTag := t.Field(i).Tag.Lookup(proc.tag)
+					if hasTag {
+						for j := 0; j < v.Field(i).Len(); j++ {
+							if err := proc.f(v.Field(i).Index(j)); err != nil {
+								return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
+							}
+						}
+					}
+				}
+
+			}
+		// Recursively process struct pointers.
+		case reflect.Ptr:
+			if v.Field(i).Elem().Kind() == reflect.Struct {
+				if err := processField(v.Field(i).Interface(), processors); err != nil {
+					return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
+				}
+			}
+		default:
+			field := t.Field(i)
+			for _, proc := range processors {
+				if _, hasTag := field.Tag.Lookup(proc.tag); hasTag {
+					if err := proc.f(v.Field(i)); err != nil {
+						return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
+					}
+				}
+			}
+		}
+	}
+	return nil
+}
+
+func hexToBase64Processor(v reflect.Value) error {
+	b, err := bytesutil.FromHexString(v.String())
+	if err != nil {
+		return err
+	}
+	v.SetString(base64.StdEncoding.EncodeToString(b))
+	return nil
+}
+
+func base64ToHexProcessor(v reflect.Value) error {
+	if v.String() == "" {
+		return nil
+	}
+	b, err := base64.StdEncoding.DecodeString(v.String())
+	if err != nil {
+		return err
+	}
+	v.SetString(hexutil.Encode(b))
+	return nil
+}
+
+func enumToLowercaseProcessor(v reflect.Value) error {
+	v.SetString(strings.ToLower(v.String()))
+	return nil
+}
+
+func timeToUnixProcessor(v reflect.Value) error {
+	t, err := time.Parse(time.RFC3339, v.String())
+	if err != nil {
+		return err
+	}
+	v.SetString(strconv.FormatUint(uint64(t.Unix()), 10))
+	return nil
+}
--- a/api/gateway/apimiddleware/process_request.go
+++ b/api/gateway/apimiddleware/process_request.go
@@ -1,27 +1,31 @@
-package gateway
+package apimiddleware

 import (
 	"bytes"
-	"encoding/base64"
 	"encoding/json"
-	"fmt"
 	"io"
 	"io/ioutil"
+	"net"
 	"net/http"
-	"reflect"
 	"strconv"
 	"strings"
-	"time"

-	"github.com/ethereum/go-ethereum/common/hexutil"
 	"github.com/pkg/errors"
 	"github.com/prysmaticlabs/prysm/api/grpc"
-	"github.com/wealdtech/go-bytesutil"
 )

 // DeserializeRequestBodyIntoContainer deserializes the request's body into an endpoint-specific struct.
 func DeserializeRequestBodyIntoContainer(body io.Reader, requestContainer interface{}) ErrorJson {
-	if err := json.NewDecoder(body).Decode(&requestContainer); err != nil {
+	decoder := json.NewDecoder(body)
+	decoder.DisallowUnknownFields()
+	if err := decoder.Decode(&requestContainer); err != nil {
+		if strings.Contains(err.Error(), "json: unknown field") {
+			e := errors.Wrap(err, "could not decode request body")
+			return &DefaultErrorJson{
+				Message: e.Error(),
+				Code:    http.StatusBadRequest,
+			}
+		}
 		return InternalServerErrorWithMessage(err, "could not decode request body")
 	}
 	return nil
@@ -62,15 +66,23 @@ func (m *ApiProxyMiddleware) PrepareRequestForProxying(endpoint Endpoint, req *h
 	if errJson := HandleURLParameters(endpoint.Path, req, endpoint.RequestURLLiterals); errJson != nil {
 		return errJson
 	}
-	return HandleQueryParameters(req, endpoint.RequestQueryParams)
+	if errJson := HandleQueryParameters(req, endpoint.RequestQueryParams); errJson != nil {
+		return errJson
+	}
+	// We have to add the prefix after handling parameters because adding the prefix changes URL segment indexing.
+	req.URL.Path = "/internal" + req.URL.Path
+	return nil
 }

 // ProxyRequest proxies the request to grpc-gateway.
-func ProxyRequest(req *http.Request) (*http.Response, ErrorJson) {
+func (m *ApiProxyMiddleware) ProxyRequest(req *http.Request) (*http.Response, ErrorJson) {
 	// We do not use http.DefaultClient because it does not have any timeout.
-	netClient := &http.Client{Timeout: time.Minute * 2}
+	netClient := &http.Client{Timeout: m.Timeout}
 	grpcResp, err := netClient.Do(req)
 	if err != nil {
+		if err, ok := err.(net.Error); ok && err.Timeout() {
+			return nil, TimeoutError()
+		}
 		return nil, InternalServerErrorWithMessage(err, "could not proxy request")
 	}
 	if grpcResp == nil {
@@ -88,26 +100,30 @@ func ReadGrpcResponseBody(r io.Reader) ([]byte, ErrorJson) {
 	return body, nil
 }

-// DeserializeGrpcResponseBodyIntoErrorJson deserializes the body from the grpc-gateway's response into an error struct.
-// The struct can be later examined to check if the request resulted in an error.
-func DeserializeGrpcResponseBodyIntoErrorJson(errJson ErrorJson, body []byte) ErrorJson {
-	if err := json.Unmarshal(body, errJson); err != nil {
-		return InternalServerErrorWithMessage(err, "could not unmarshal error")
-	}
-	return nil
-}
-
 // HandleGrpcResponseError acts on an error that resulted from a grpc-gateway's response.
-func HandleGrpcResponseError(errJson ErrorJson, resp *http.Response, w http.ResponseWriter) {
-	// Something went wrong, but the request completed, meaning we can write headers and the error message.
-	for h, vs := range resp.Header {
-		for _, v := range vs {
-			w.Header().Set(h, v)
+func HandleGrpcResponseError(errJson ErrorJson, resp *http.Response, respBody []byte, w http.ResponseWriter) (bool, ErrorJson) {
+	responseHasError := false
+	if err := json.Unmarshal(respBody, errJson); err != nil {
+		return false, InternalServerErrorWithMessage(err, "could not unmarshal error")
+	}
+	if errJson.Msg() != "" {
+		responseHasError = true
+		// Something went wrong, but the request completed, meaning we can write headers and the error message.
+		for h, vs := range resp.Header {
+			for _, v := range vs {
+				w.Header().Set(h, v)
+			}
+		}
+		// Handle gRPC timeout.
+		if resp.StatusCode == http.StatusGatewayTimeout {
+			WriteError(w, TimeoutError(), resp.Header)
+		} else {
+			// Set code to HTTP code because unmarshalled body contained gRPC code.
+			errJson.SetCode(resp.StatusCode)
+			WriteError(w, errJson, resp.Header)
 		}
 	}
-	// Set code to HTTP code because unmarshalled body contained gRPC code.
-	errJson.SetCode(resp.StatusCode)
-	WriteError(w, errJson, resp.Header)
+	return responseHasError, nil
 }

 // GrpcResponseIsEmpty determines whether the grpc-gateway's response body contains no data.
@@ -192,9 +208,11 @@ func WriteMiddlewareResponseHeadersAndBody(grpcResp *http.Response, responseJson
 // WriteError writes the error by manipulating headers and the body of the final response.
 func WriteError(w http.ResponseWriter, errJson ErrorJson, responseHeader http.Header) {
 	// Include custom error in the error JSON.
+	hasCustomError := false
 	if responseHeader != nil {
 		customError, ok := responseHeader["Grpc-Metadata-"+grpc.CustomErrorMetadataKey]
 		if ok {
+			hasCustomError = true
 			// Assume header has only one value and read the 0 index.
 			if err := json.Unmarshal([]byte(customError[0]), errJson); err != nil {
 				log.WithError(err).Error("Could not unmarshal custom error message")
@@ -203,10 +221,29 @@ func WriteError(w http.ResponseWriter, errJson ErrorJson, responseHeader http.He
 		}
 	}

-	j, err := json.Marshal(errJson)
-	if err != nil {
-		log.WithError(err).Error("Could not marshal error message")
-		return
+	var j []byte
+	if hasCustomError {
+		var err error
+		j, err = json.Marshal(errJson)
+		if err != nil {
+			log.WithError(err).Error("Could not marshal error message")
+			return
+		}
+	} else {
+		var err error
+		// We marshal the response body into a DefaultErrorJson if the custom error is not present.
+		// This is because the ErrorJson argument is the endpoint's error definition, which may contain custom fields.
+		// In such a scenario marhaling the endpoint's error would populate the resulting JSON
+		// with these fields even if they are not present in the gRPC header.
+		d := &DefaultErrorJson{
+			Message: errJson.Msg(),
+			Code:    errJson.StatusCode(),
+		}
+		j, err = json.Marshal(d)
+		if err != nil {
+			log.WithError(err).Error("Could not marshal error message")
+			return
+		}
 	}

 	w.Header().Set("Content-Length", strconv.Itoa(len(j)))
@@ -224,97 +261,3 @@ func Cleanup(grpcResponseBody io.ReadCloser) ErrorJson {
 	}
 	return nil
 }
-
-// processField calls each processor function on any field that has the matching tag set.
-// It is a recursive function.
-func processField(s interface{}, processors []fieldProcessor) error {
-	kind := reflect.TypeOf(s).Kind()
-	if kind != reflect.Ptr && kind != reflect.Slice && kind != reflect.Array {
-		return fmt.Errorf("processing fields of kind '%v' is unsupported", kind)
-	}
-
-	t := reflect.TypeOf(s).Elem()
-	v := reflect.Indirect(reflect.ValueOf(s))
-
-	for i := 0; i < t.NumField(); i++ {
-		switch v.Field(i).Kind() {
-		case reflect.Slice:
-			sliceElem := t.Field(i).Type.Elem()
-			kind := sliceElem.Kind()
-			// Recursively process slices to struct pointers.
-			if kind == reflect.Ptr && sliceElem.Elem().Kind() == reflect.Struct {
-				for j := 0; j < v.Field(i).Len(); j++ {
-					if err := processField(v.Field(i).Index(j).Interface(), processors); err != nil {
-						return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
-					}
-				}
-			}
-			// Process each string in string slices.
-			if kind == reflect.String {
-				for _, proc := range processors {
-					_, hasTag := t.Field(i).Tag.Lookup(proc.tag)
-					if hasTag {
-						for j := 0; j < v.Field(i).Len(); j++ {
-							if err := proc.f(v.Field(i).Index(j)); err != nil {
-								return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
-							}
-						}
-					}
-				}
-
-			}
-		// Recursively process struct pointers.
-		case reflect.Ptr:
-			if v.Field(i).Elem().Kind() == reflect.Struct {
-				if err := processField(v.Field(i).Interface(), processors); err != nil {
-					return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
-				}
-			}
-		default:
-			field := t.Field(i)
-			for _, proc := range processors {
-				if _, hasTag := field.Tag.Lookup(proc.tag); hasTag {
-					if err := proc.f(v.Field(i)); err != nil {
-						return errors.Wrapf(err, "could not process field '%s'", t.Field(i).Name)
-					}
-				}
-			}
-		}
-	}
-	return nil
-}
-
-func hexToBase64Processor(v reflect.Value) error {
-	b, err := bytesutil.FromHexString(v.String())
-	if err != nil {
-		return err
-	}
-	v.SetString(base64.StdEncoding.EncodeToString(b))
-	return nil
-}
-
-func base64ToHexProcessor(v reflect.Value) error {
-	if v.String() == "" {
-		return nil
-	}
-	b, err := base64.StdEncoding.DecodeString(v.String())
-	if err != nil {
-		return err
-	}
-	v.SetString(hexutil.Encode(b))
-	return nil
-}
-
-func enumToLowercaseProcessor(v reflect.Value) error {
-	v.SetString(strings.ToLower(v.String()))
-	return nil
-}
-
-func timeToUnixProcessor(v reflect.Value) error {
-	t, err := time.Parse(time.RFC3339, v.String())
-	if err != nil {
-		return err
-	}
-	v.SetString(strconv.FormatUint(uint64(t.Unix()), 10))
-	return nil
-}
--- a/api/gateway/apimiddleware/process_request_test.go
+++ b/api/gateway/apimiddleware/process_request_test.go
@@ -1,4 +1,4 @@
-package gateway
+package apimiddleware

 import (
 	"bytes"
@@ -9,8 +9,8 @@ import (
 	"testing"

 	"github.com/prysmaticlabs/prysm/api/grpc"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	"github.com/sirupsen/logrus/hooks/test"
 )

@@ -63,6 +63,11 @@ func (e *testErrorJson) SetCode(code int) {
 	e.Code = code
 }

+// SetMsg sets the error's underlying message.
+func (e *testErrorJson) SetMsg(msg string) {
+	e.Message = msg
+}
+
 func TestDeserializeRequestBodyIntoContainer(t *testing.T) {
 	t.Run("ok", func(t *testing.T) {
 		var bodyJson bytes.Buffer
@@ -83,6 +88,15 @@ func TestDeserializeRequestBodyIntoContainer(t *testing.T) {
 		assert.Equal(t, true, strings.Contains(errJson.Msg(), "could not decode request body"))
 		assert.Equal(t, http.StatusInternalServerError, errJson.StatusCode())
 	})
+
+	t.Run("unknown field", func(t *testing.T) {
+		var bodyJson bytes.Buffer
+		bodyJson.Write([]byte("{\"foo\":\"foo\"}"))
+		errJson := DeserializeRequestBodyIntoContainer(&bodyJson, &testRequestContainer{})
+		require.NotNil(t, errJson)
+		assert.Equal(t, true, strings.Contains(errJson.Msg(), "could not decode request body"))
+		assert.Equal(t, http.StatusBadRequest, errJson.StatusCode())
+	})
 }

 func TestProcessRequestContainerFields(t *testing.T) {
@@ -147,29 +161,6 @@ func TestReadGrpcResponseBody(t *testing.T) {
 	assert.Equal(t, "foo", string(body))
 }

-func TestDeserializeGrpcResponseBodyIntoErrorJson(t *testing.T) {
-	t.Run("ok", func(t *testing.T) {
-		e := &testErrorJson{
-			Message: "foo",
-			Code:    500,
-		}
-		body, err := json.Marshal(e)
-		require.NoError(t, err)
-
-		eToDeserialize := &testErrorJson{}
-		errJson := DeserializeGrpcResponseBodyIntoErrorJson(eToDeserialize, body)
-		require.Equal(t, true, errJson == nil)
-		assert.Equal(t, "foo", eToDeserialize.Msg())
-		assert.Equal(t, 500, eToDeserialize.StatusCode())
-	})
-
-	t.Run("error", func(t *testing.T) {
-		errJson := DeserializeGrpcResponseBodyIntoErrorJson(nil, nil)
-		require.NotNil(t, errJson)
-		assert.Equal(t, true, strings.Contains(errJson.Msg(), "could not unmarshal error"))
-	})
-}
-
 func TestHandleGrpcResponseError(t *testing.T) {
 	response := &http.Response{
 		StatusCode: 400,
@@ -181,10 +172,14 @@ func TestHandleGrpcResponseError(t *testing.T) {
 	writer := httptest.NewRecorder()
 	errJson := &testErrorJson{
 		Message: "foo",
-		Code:    500,
+		Code:    400,
 	}
+	b, err := json.Marshal(errJson)
+	require.NoError(t, err)

-	HandleGrpcResponseError(errJson, response, writer)
+	hasError, e := HandleGrpcResponseError(errJson, response, b, writer)
+	require.Equal(t, true, e == nil)
+	assert.Equal(t, true, hasError)
 	v, ok := writer.Header()["Foo"]
 	require.Equal(t, true, ok, "header not found")
 	require.Equal(t, 1, len(v), "wrong number of header values")
--- a/api/gateway/api_middleware_structs.go
+++ b/api/gateway/api_middleware_structs.go
@@ -1,4 +1,4 @@
-package gateway
+package apimiddleware

 import (
 	"net/http"
@@ -15,6 +15,7 @@ type ErrorJson interface {
 	StatusCode() int
 	SetCode(code int)
 	Msg() string
+	SetMsg(msg string)
 }

 // DefaultErrorJson is a JSON representation of a simple error value, containing only a message and an error code.
@@ -40,6 +41,13 @@ func InternalServerError(err error) *DefaultErrorJson {
 	}
 }

+func TimeoutError() *DefaultErrorJson {
+	return &DefaultErrorJson{
+		Message: "Request timeout",
+		Code:    http.StatusRequestTimeout,
+	}
+}
+
 // StatusCode returns the error's underlying error code.
 func (e *DefaultErrorJson) StatusCode() int {
 	return e.Code
@@ -54,3 +62,8 @@ func (e *DefaultErrorJson) Msg() string {
 func (e *DefaultErrorJson) SetCode(code int) {
 	e.Code = code
 }
+
+// SetMsg sets the error's underlying message.
+func (e *DefaultErrorJson) SetMsg(msg string) {
+	e.Message = msg
+}
--- a/api/gateway/gateway.go
+++ b/api/gateway/gateway.go
@@ -10,8 +10,10 @@ import (
 	"strings"
 	"time"

+	"github.com/gorilla/mux"
 	gwruntime "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
 	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/api/gateway/apimiddleware"
 	"github.com/prysmaticlabs/prysm/runtime"
 	"github.com/rs/cors"
 	"google.golang.org/grpc"
@@ -25,83 +27,59 @@ var _ runtime.Service = (*Gateway)(nil)
 type PbMux struct {
 	Registrations []PbHandlerRegistration // Protobuf registrations to be registered in Mux.
 	Patterns      []string                // URL patterns that will be handled by Mux.
-	Mux           *gwruntime.ServeMux     // The mux that will be used for grpc-gateway requests.
+	Mux           *gwruntime.ServeMux     // The router that will be used for grpc-gateway requests.
 }

 // PbHandlerRegistration is a function that registers a protobuf handler.
 type PbHandlerRegistration func(context.Context, *gwruntime.ServeMux, *grpc.ClientConn) error

 // MuxHandler is a function that implements the mux handler functionality.
-type MuxHandler func(http.Handler, http.ResponseWriter, *http.Request)
+type MuxHandler func(
+	apiMiddlewareHandler *apimiddleware.ApiProxyMiddleware,
+	h http.HandlerFunc,
+	w http.ResponseWriter,
+	req *http.Request,
+)
+
+// Config parameters for setting up the gateway service.
+type config struct {
+	maxCallRecvMsgSize           uint64
+	remoteCert                   string
+	gatewayAddr                  string
+	remoteAddr                   string
+	allowedOrigins               []string
+	apiMiddlewareEndpointFactory apimiddleware.EndpointFactory
+	muxHandler                   MuxHandler
+	pbHandlers                   []*PbMux
+	router                       *mux.Router
+	timeout                      time.Duration
+}

 // Gateway is the gRPC gateway to serve HTTP JSON traffic as a proxy and forward it to the gRPC server.
 type Gateway struct {
-	conn                         *grpc.ClientConn
-	pbHandlers                   []PbMux
-	muxHandler                   MuxHandler
-	maxCallRecvMsgSize           uint64
-	mux                          *http.ServeMux
-	server                       *http.Server
-	cancel                       context.CancelFunc
-	remoteCert                   string
-	gatewayAddr                  string
-	apiMiddlewareAddr            string
-	apiMiddlewareEndpointFactory EndpointFactory
-	ctx                          context.Context
-	startFailure                 error
-	remoteAddr                   string
-	allowedOrigins               []string
+	cfg          *config
+	conn         *grpc.ClientConn
+	server       *http.Server
+	cancel       context.CancelFunc
+	proxy        *apimiddleware.ApiProxyMiddleware
+	ctx          context.Context
+	startFailure error
 }

 // New returns a new instance of the Gateway.
-func New(
-	ctx context.Context,
-	pbHandlers []PbMux,
-	muxHandler MuxHandler,
-	remoteAddr,
-	gatewayAddress string,
-) *Gateway {
+func New(ctx context.Context, opts ...Option) (*Gateway, error) {
 	g := &Gateway{
-		pbHandlers:     pbHandlers,
-		muxHandler:     muxHandler,
-		mux:            http.NewServeMux(),
-		gatewayAddr:    gatewayAddress,
-		ctx:            ctx,
-		remoteAddr:     remoteAddr,
-		allowedOrigins: []string{},
+		ctx: ctx,
+		cfg: &config{
+			router: mux.NewRouter(),
+		},
 	}
-	return g
-}
-
-// WithMux allows adding a custom http.ServeMux to the gateway.
-func (g *Gateway) WithMux(m *http.ServeMux) *Gateway {
-	g.mux = m
-	return g
-}
-
-// WithAllowedOrigins allows adding a set of allowed origins to the gateway.
-func (g *Gateway) WithAllowedOrigins(origins []string) *Gateway {
-	g.allowedOrigins = origins
-	return g
-}
-
-// WithRemoteCert allows adding a custom certificate to the gateway,
-func (g *Gateway) WithRemoteCert(cert string) *Gateway {
-	g.remoteCert = cert
-	return g
-}
-
-// WithMaxCallRecvMsgSize allows specifying the maximum allowed gRPC message size.
-func (g *Gateway) WithMaxCallRecvMsgSize(size uint64) *Gateway {
-	g.maxCallRecvMsgSize = size
-	return g
-}
-
-// WithApiMiddleware allows adding API Middleware proxy to the gateway.
-func (g *Gateway) WithApiMiddleware(address string, endpointFactory EndpointFactory) *Gateway {
-	g.apiMiddlewareAddr = address
-	g.apiMiddlewareEndpointFactory = endpointFactory
-	return g
+	for _, opt := range opts {
+		if err := opt(g); err != nil {
+			return nil, err
+		}
+	}
+	return g, nil
 }

 // Start the gateway service.
@@ -109,7 +87,7 @@ func (g *Gateway) Start() {
 	ctx, cancel := context.WithCancel(g.ctx)
 	g.cancel = cancel

-	conn, err := g.dial(ctx, "tcp", g.remoteAddr)
+	conn, err := g.dial(ctx, "tcp", g.cfg.remoteAddr)
 	if err != nil {
 		log.WithError(err).Error("Failed to connect to gRPC server")
 		g.startFailure = err
@@ -117,7 +95,7 @@ func (g *Gateway) Start() {
 	}
 	g.conn = conn

-	for _, h := range g.pbHandlers {
+	for _, h := range g.cfg.pbHandlers {
 		for _, r := range h.Registrations {
 			if err := r(ctx, h.Mux, g.conn); err != nil {
 				log.WithError(err).Error("Failed to register handler")
@@ -126,35 +104,35 @@ func (g *Gateway) Start() {
 			}
 		}
 		for _, p := range h.Patterns {
-			g.mux.Handle(p, h.Mux)
+			g.cfg.router.PathPrefix(p).Handler(h.Mux)
 		}
 	}

-	corsMux := g.corsMiddleware(g.mux)
+	corsMux := g.corsMiddleware(g.cfg.router)

-	if g.muxHandler != nil {
-		g.mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
-			g.muxHandler(corsMux, w, r)
+	if g.cfg.apiMiddlewareEndpointFactory != nil && !g.cfg.apiMiddlewareEndpointFactory.IsNil() {
+		g.registerApiMiddleware()
+	}
+
+	if g.cfg.muxHandler != nil {
+		g.cfg.router.PathPrefix("/").HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			g.cfg.muxHandler(g.proxy, corsMux.ServeHTTP, w, r)
 		})
 	}

 	g.server = &http.Server{
-		Addr:    g.gatewayAddr,
+		Addr:    g.cfg.gatewayAddr,
 		Handler: corsMux,
 	}

 	go func() {
-		log.WithField("address", g.gatewayAddr).Info("Starting gRPC gateway")
+		log.WithField("address", g.cfg.gatewayAddr).Info("Starting gRPC gateway")
 		if err := g.server.ListenAndServe(); err != http.ErrServerClosed {
 			log.WithError(err).Error("Failed to start gRPC gateway")
 			g.startFailure = err
 			return
 		}
 	}()
-
-	if g.apiMiddlewareAddr != "" && g.apiMiddlewareEndpointFactory != nil && !g.apiMiddlewareEndpointFactory.IsNil() {
-		go g.registerApiMiddleware()
-	}
 }

 // Status of grpc gateway. Returns an error if this service is unhealthy.
@@ -162,11 +140,9 @@ func (g *Gateway) Status() error {
 	if g.startFailure != nil {
 		return g.startFailure
 	}
-
 	if s := g.conn.GetState(); s != connectivity.Ready {
 		return fmt.Errorf("grpc server is %s", s)
 	}
-
 	return nil
 }

@@ -183,18 +159,16 @@ func (g *Gateway) Stop() error {
 			}
 		}
 	}
-
 	if g.cancel != nil {
 		g.cancel()
 	}
-
 	return nil
 }

 func (g *Gateway) corsMiddleware(h http.Handler) http.Handler {
 	c := cors.New(cors.Options{
-		AllowedOrigins:   g.allowedOrigins,
-		AllowedMethods:   []string{http.MethodPost, http.MethodGet, http.MethodOptions},
+		AllowedOrigins:   g.cfg.allowedOrigins,
+		AllowedMethods:   []string{http.MethodPost, http.MethodGet, http.MethodDelete, http.MethodOptions},
 		AllowCredentials: true,
 		MaxAge:           600,
 		AllowedHeaders:   []string{"*"},
@@ -236,8 +210,8 @@ func (g *Gateway) dial(ctx context.Context, network, addr string) (*grpc.ClientC
 // "addr" must be a valid TCP address with a port number.
 func (g *Gateway) dialTCP(ctx context.Context, addr string) (*grpc.ClientConn, error) {
 	security := grpc.WithInsecure()
-	if len(g.remoteCert) > 0 {
-		creds, err := credentials.NewClientTLSFromFile(g.remoteCert, "")
+	if len(g.cfg.remoteCert) > 0 {
+		creds, err := credentials.NewClientTLSFromFile(g.cfg.remoteCert, "")
 		if err != nil {
 			return nil, err
 		}
@@ -245,7 +219,7 @@ func (g *Gateway) dialTCP(ctx context.Context, addr string) (*grpc.ClientConn, e
 	}
 	opts := []grpc.DialOption{
 		security,
-		grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(int(g.maxCallRecvMsgSize))),
+		grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(int(g.cfg.maxCallRecvMsgSize))),
 	}

 	return grpc.DialContext(ctx, addr, opts...)
@@ -266,21 +240,17 @@ func (g *Gateway) dialUnix(ctx context.Context, addr string) (*grpc.ClientConn,
 	opts := []grpc.DialOption{
 		grpc.WithInsecure(),
 		grpc.WithContextDialer(f),
-		grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(int(g.maxCallRecvMsgSize))),
+		grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(int(g.cfg.maxCallRecvMsgSize))),
 	}
 	return grpc.DialContext(ctx, addr, opts...)
 }

 func (g *Gateway) registerApiMiddleware() {
-	proxy := &ApiProxyMiddleware{
-		GatewayAddress:  g.gatewayAddr,
-		ProxyAddress:    g.apiMiddlewareAddr,
-		EndpointCreator: g.apiMiddlewareEndpointFactory,
-	}
-	log.WithField("API middleware address", g.apiMiddlewareAddr).Info("Starting API middleware")
-	if err := proxy.Run(); err != http.ErrServerClosed {
-		log.WithError(err).Error("Failed to start API middleware")
-		g.startFailure = err
-		return
+	g.proxy = &apimiddleware.ApiProxyMiddleware{
+		GatewayAddress:  g.cfg.gatewayAddr,
+		EndpointCreator: g.cfg.apiMiddlewareEndpointFactory,
+		Timeout:         g.cfg.timeout,
 	}
+	log.Info("Starting API middleware")
+	g.proxy.Run(g.cfg.router)
 }
--- a/api/gateway/gateway_test.go
+++ b/api/gateway/gateway_test.go
@@ -9,9 +9,11 @@ import (
 	"net/url"
 	"testing"

+	"github.com/gorilla/mux"
+	"github.com/prysmaticlabs/prysm/api/gateway/apimiddleware"
 	"github.com/prysmaticlabs/prysm/cmd/beacon-chain/flags"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 	"github.com/urfave/cli/v2"
 )
@@ -23,7 +25,7 @@ func (*mockEndpointFactory) Paths() []string {
 	return []string{}
 }

-func (*mockEndpointFactory) Create(_ string) (*Endpoint, error) {
+func (*mockEndpointFactory) Create(_ string) (*apimiddleware.Endpoint, error) {
 	return nil, nil
 }

@@ -32,34 +34,36 @@ func (*mockEndpointFactory) IsNil() bool {
 }

 func TestGateway_Customized(t *testing.T) {
-	mux := http.NewServeMux()
+	r := mux.NewRouter()
 	cert := "cert"
 	origins := []string{"origin"}
 	size := uint64(100)
-	middlewareAddr := "middleware"
 	endpointFactory := &mockEndpointFactory{}

-	g := New(
-		context.Background(),
-		[]PbMux{},
-		func(handler http.Handler, writer http.ResponseWriter, request *http.Request) {
+	opts := []Option{
+		WithRouter(r),
+		WithRemoteCert(cert),
+		WithAllowedOrigins(origins),
+		WithMaxCallRecvMsgSize(size),
+		WithApiMiddleware(endpointFactory),
+		WithMuxHandler(func(
+			_ *apimiddleware.ApiProxyMiddleware,
+			_ http.HandlerFunc,
+			_ http.ResponseWriter,
+			_ *http.Request,
+		) {
+		}),
+	}

-		},
-		"",
-		"",
-	).WithMux(mux).
-		WithRemoteCert(cert).
-		WithAllowedOrigins(origins).
-		WithMaxCallRecvMsgSize(size).
-		WithApiMiddleware(middlewareAddr, endpointFactory)
+	g, err := New(context.Background(), opts...)
+	require.NoError(t, err)

-	assert.Equal(t, mux, g.mux)
-	assert.Equal(t, cert, g.remoteCert)
-	require.Equal(t, 1, len(g.allowedOrigins))
-	assert.Equal(t, origins[0], g.allowedOrigins[0])
-	assert.Equal(t, size, g.maxCallRecvMsgSize)
-	assert.Equal(t, middlewareAddr, g.apiMiddlewareAddr)
-	assert.Equal(t, endpointFactory, g.apiMiddlewareEndpointFactory)
+	assert.Equal(t, r, g.cfg.router)
+	assert.Equal(t, cert, g.cfg.remoteCert)
+	require.Equal(t, 1, len(g.cfg.allowedOrigins))
+	assert.Equal(t, origins[0], g.cfg.allowedOrigins[0])
+	assert.Equal(t, size, g.cfg.maxCallRecvMsgSize)
+	assert.Equal(t, endpointFactory, g.cfg.apiMiddlewareEndpointFactory)
 }

 func TestGateway_StartStop(t *testing.T) {
@@ -75,23 +79,27 @@ func TestGateway_StartStop(t *testing.T) {
 	selfAddress := fmt.Sprintf("%s:%d", rpcHost, ctx.Int(flags.RPCPort.Name))
 	gatewayAddress := fmt.Sprintf("%s:%d", gatewayHost, gatewayPort)

-	g := New(
-		ctx.Context,
-		[]PbMux{},
-		func(handler http.Handler, writer http.ResponseWriter, request *http.Request) {
+	opts := []Option{
+		WithGatewayAddr(gatewayAddress),
+		WithRemoteAddr(selfAddress),
+		WithMuxHandler(func(
+			_ *apimiddleware.ApiProxyMiddleware,
+			_ http.HandlerFunc,
+			_ http.ResponseWriter,
+			_ *http.Request,
+		) {
+		}),
+	}

-		},
-		selfAddress,
-		gatewayAddress,
-	)
+	g, err := New(context.Background(), opts...)
+	require.NoError(t, err)

 	g.Start()
 	go func() {
 		require.LogsContain(t, hook, "Starting gRPC gateway")
 		require.LogsDoNotContain(t, hook, "Starting API middleware")
 	}()
-
-	err := g.Stop()
+	err = g.Stop()
 	require.NoError(t, err)
 }

@@ -106,15 +114,15 @@ func TestGateway_NilHandler_NotFoundHandlerRegistered(t *testing.T) {
 	selfAddress := fmt.Sprintf("%s:%d", rpcHost, ctx.Int(flags.RPCPort.Name))
 	gatewayAddress := fmt.Sprintf("%s:%d", gatewayHost, gatewayPort)

-	g := New(
-		ctx.Context,
-		[]PbMux{},
-		/* muxHandler */ nil,
-		selfAddress,
-		gatewayAddress,
-	)
+	opts := []Option{
+		WithGatewayAddr(gatewayAddress),
+		WithRemoteAddr(selfAddress),
+	}
+
+	g, err := New(context.Background(), opts...)
+	require.NoError(t, err)

 	writer := httptest.NewRecorder()
-	g.mux.ServeHTTP(writer, &http.Request{Method: "GET", Host: "localhost", URL: &url.URL{Path: "/foo"}})
+	g.cfg.router.ServeHTTP(writer, &http.Request{Method: "GET", Host: "localhost", URL: &url.URL{Path: "/foo"}})
 	assert.Equal(t, http.StatusNotFound, writer.Code)
 }
--- a/api/gateway/options.go
+++ b/api/gateway/options.go
@@ -0,0 +1,93 @@
+package gateway
+
+import (
+	"time"
+
+	"github.com/gorilla/mux"
+	gwruntime "github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
+	"github.com/prysmaticlabs/prysm/api/gateway/apimiddleware"
+)
+
+type Option func(g *Gateway) error
+
+func (g *Gateway) SetRouter(r *mux.Router) *Gateway {
+	g.cfg.router = r
+	return g
+}
+
+func WithPbHandlers(handlers []*PbMux) Option {
+	return func(g *Gateway) error {
+		g.cfg.pbHandlers = handlers
+		return nil
+	}
+}
+
+func WithMuxHandler(m MuxHandler) Option {
+	return func(g *Gateway) error {
+		g.cfg.muxHandler = m
+		return nil
+	}
+}
+
+func WithGatewayAddr(addr string) Option {
+	return func(g *Gateway) error {
+		g.cfg.gatewayAddr = addr
+		return nil
+	}
+}
+
+func WithRemoteAddr(addr string) Option {
+	return func(g *Gateway) error {
+		g.cfg.remoteAddr = addr
+		return nil
+	}
+}
+
+// WithRouter allows adding a custom mux router to the gateway.
+func WithRouter(r *mux.Router) Option {
+	return func(g *Gateway) error {
+		g.cfg.router = r
+		return nil
+	}
+}
+
+// WithAllowedOrigins allows adding a set of allowed origins to the gateway.
+func WithAllowedOrigins(origins []string) Option {
+	return func(g *Gateway) error {
+		g.cfg.allowedOrigins = origins
+		return nil
+	}
+}
+
+// WithRemoteCert allows adding a custom certificate to the gateway,
+func WithRemoteCert(cert string) Option {
+	return func(g *Gateway) error {
+		g.cfg.remoteCert = cert
+		return nil
+	}
+}
+
+// WithMaxCallRecvMsgSize allows specifying the maximum allowed gRPC message size.
+func WithMaxCallRecvMsgSize(size uint64) Option {
+	return func(g *Gateway) error {
+		g.cfg.maxCallRecvMsgSize = size
+		return nil
+	}
+}
+
+// WithApiMiddleware allows adding an API middleware proxy to the gateway.
+func WithApiMiddleware(endpointFactory apimiddleware.EndpointFactory) Option {
+	return func(g *Gateway) error {
+		g.cfg.apiMiddlewareEndpointFactory = endpointFactory
+		return nil
+	}
+}
+
+// WithTimeout allows changing the timeout value for API calls.
+func WithTimeout(seconds uint64) Option {
+	return func(g *Gateway) error {
+		g.cfg.timeout = time.Second * time.Duration(seconds)
+		gwruntime.DefaultContextTimeout = time.Second * time.Duration(seconds)
+		return nil
+	}
+}
--- a/api/grpc/BUILD.bazel
+++ b/api/grpc/BUILD.bazel
@@ -20,8 +20,8 @@ go_test(
    srcs = ["grpcutils_test.go"],
    embed = [":go_default_library"],
    deps = [
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
        "@com_github_grpc_ecosystem_grpc_gateway_v2//runtime:go_default_library",
        "@com_github_sirupsen_logrus//hooks/test:go_default_library",
        "@org_golang_google_grpc//:go_default_library",
--- a/api/grpc/grpcutils_test.go
+++ b/api/grpc/grpcutils_test.go
@@ -7,8 +7,8 @@ import (
 	"testing"

 	"github.com/grpc-ecosystem/grpc-gateway/v2/runtime"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/metadata"
--- a/api/pagination/BUILD.bazel
+++ b/api/pagination/BUILD.bazel
@@ -6,7 +6,7 @@ go_library(
    importpath = "github.com/prysmaticlabs/prysm/api/pagination",
    visibility = ["//visibility:public"],
    deps = [
-        "//shared/params:go_default_library",
+        "//config/params:go_default_library",
        "@com_github_pkg_errors//:go_default_library",
    ],
 )
@@ -16,7 +16,7 @@ go_test(
    srcs = ["pagination_test.go"],
    deps = [
        ":go_default_library",
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
    ],
 )
--- a/api/pagination/pagination.go
+++ b/api/pagination/pagination.go
@@ -6,7 +6,7 @@ import (
 	"strconv"

 	"github.com/pkg/errors"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/config/params"
 )

 // StartAndEndPage takes in the requested page token, wanted page size, total page size.
--- a/api/pagination/pagination_test.go
+++ b/api/pagination/pagination_test.go
@@ -4,8 +4,8 @@ import (
 	"testing"

 	"github.com/prysmaticlabs/prysm/api/pagination"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 func TestStartAndEndPage(t *testing.T) {
--- a/async/BUILD.bazel
+++ b/async/BUILD.bazel
@@ -24,9 +24,9 @@ go_test(
    ],
    embed = [":go_default_library"],
    deps = [
-        "//shared/testutil:go_default_library",
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
+        "//testing/util:go_default_library",
        "@com_github_sirupsen_logrus//:go_default_library",
        "@com_github_stretchr_testify//assert:go_default_library",
    ],
--- a/async/benchmark_test.go
+++ b/async/benchmark_test.go
@@ -7,7 +7,7 @@ import (
 	"testing"

 	"github.com/prysmaticlabs/prysm/async"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	log "github.com/sirupsen/logrus"
 )

--- a/async/debounce_test.go
+++ b/async/debounce_test.go
@@ -7,9 +7,9 @@ import (
 	"time"

 	"github.com/prysmaticlabs/prysm/async"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
 )

 func TestDebounce_NoEvents(t *testing.T) {
@@ -30,7 +30,7 @@ func TestDebounce_NoEvents(t *testing.T) {
 		})
 		wg.Done()
 	}()
-	if testutil.WaitTimeout(wg, interval*2) {
+	if util.WaitTimeout(wg, interval*2) {
 		t.Fatalf("Test should have exited by now, timed out")
 	}
 	assert.Equal(t, 0, timesHandled, "Wrong number of handled calls")
@@ -66,7 +66,7 @@ func TestDebounce_CtxClosing(t *testing.T) {
 		})
 		wg.Done()
 	}()
-	if testutil.WaitTimeout(wg, interval*2) {
+	if util.WaitTimeout(wg, interval*2) {
 		t.Fatalf("Test should have exited by now, timed out")
 	}
 	assert.Equal(t, 0, timesHandled, "Wrong number of handled calls")
--- a/async/event/BUILD.bazel
+++ b/async/event/BUILD.bazel
@@ -23,7 +23,7 @@ go_test(
    ],
    embed = [":go_default_library"],
    deps = [
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
    ],
 )
--- a/async/event/feed_test.go
+++ b/async/event/feed_test.go
@@ -23,7 +23,7 @@ import (
 	"testing"
 	"time"

-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
+	"github.com/prysmaticlabs/prysm/testing/assert"
 )

 func TestFeedPanics(t *testing.T) {
--- a/async/event/subscription_test.go
+++ b/async/event/subscription_test.go
@@ -23,7 +23,7 @@ import (
 	"testing"
 	"time"

-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 var errInts = errors.New("error in subscribeInts")
--- a/async/every.go
+++ b/async/every.go
@@ -1,4 +1,4 @@
-// Package runutil includes helpers for scheduling runnable, periodic functions.
+// Package async includes helpers for scheduling runnable, periodic functions and contains useful helpers for converting multi-processor computation.
 package async

 import (
--- a/async/multilock_test.go
+++ b/async/multilock_test.go
@@ -50,7 +50,7 @@ func TestGetChan(t *testing.T) {
 	assert.Equal(ch1, ch3)
 }

-func TestLockUnlock(t *testing.T) {
+func TestLockUnlock(_ *testing.T) {
 	var wg sync.WaitGroup

 	wg.Add(5)
@@ -110,9 +110,8 @@ func TestLockUnlock_CleansUnused(t *testing.T) {
 		lock := NewMultilock("dog", "cat", "owl")
 		lock.Lock()
 		assert.Equal(t, 3, len(locks.list))
-		defer lock.Unlock()
+		lock.Unlock()

-		<-time.After(100 * time.Millisecond)
 		wg.Done()
 	}()
 	wg.Wait()
--- a/async/scatter.go
+++ b/async/scatter.go
@@ -1,5 +1,3 @@
-// Package mputil contains useful helpers for converting
-// multi-processor computation.
 package async

 import (
--- a/async/scatter_test.go
+++ b/async/scatter_test.go
@@ -6,8 +6,8 @@ import (
 	"testing"

 	"github.com/prysmaticlabs/prysm/async"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 func TestDouble(t *testing.T) {
--- a/beacon-chain/blockchain/BUILD.bazel
+++ b/beacon-chain/blockchain/BUILD.bazel
@@ -4,12 +4,16 @@ go_library(
    name = "go_default_library",
    srcs = [
        "chain_info.go",
+        "error.go",
        "head.go",
        "head_sync_committee_info.go",
-        "info.go",
        "init_sync_process_block.go",
        "log.go",
        "metrics.go",
+        "new_slot.go",
+        "optimistic_sync.go",
+        "options.go",
+        "pow_block.go",
        "process_attestation.go",
        "process_attestation_helpers.go",
        "process_block.go",
@@ -17,49 +21,62 @@ go_library(
        "receive_attestation.go",
        "receive_block.go",
        "service.go",
+        "state_balance_cache.go",
        "weak_subjectivity_checks.go",
    ],
    importpath = "github.com/prysmaticlabs/prysm/beacon-chain/blockchain",
    visibility = [
        "//beacon-chain:__subpackages__",
-        "//testing/fuzz:__pkg__",
+        "//cmd/beacon-chain:__subpackages__",
+        "//testing/slasher/simulator:__pkg__",
+        "//testing/spectest:__subpackages__",
    ],
    deps = [
        "//async:go_default_library",
+        "//async/event:go_default_library",
+        "//beacon-chain/blockchain/store:go_default_library",
        "//beacon-chain/cache:go_default_library",
        "//beacon-chain/cache/depositcache:go_default_library",
-        "//beacon-chain/core:go_default_library",
        "//beacon-chain/core/altair:go_default_library",
+        "//beacon-chain/core/blocks:go_default_library",
        "//beacon-chain/core/epoch/precompute:go_default_library",
        "//beacon-chain/core/feed:go_default_library",
        "//beacon-chain/core/feed/state:go_default_library",
        "//beacon-chain/core/helpers:go_default_library",
+        "//beacon-chain/core/signing:go_default_library",
+        "//beacon-chain/core/time:go_default_library",
        "//beacon-chain/core/transition:go_default_library",
        "//beacon-chain/db:go_default_library",
        "//beacon-chain/db/filters:go_default_library",
        "//beacon-chain/forkchoice:go_default_library",
+        "//beacon-chain/forkchoice/doubly-linked-tree:go_default_library",
        "//beacon-chain/forkchoice/protoarray:go_default_library",
        "//beacon-chain/operations/attestations:go_default_library",
        "//beacon-chain/operations/slashings:go_default_library",
        "//beacon-chain/operations/voluntaryexits:go_default_library",
        "//beacon-chain/p2p:go_default_library",
        "//beacon-chain/powchain:go_default_library",
+        "//beacon-chain/powchain/engine-api-client/v1:go_default_library",
        "//beacon-chain/state:go_default_library",
        "//beacon-chain/state/stategen:go_default_library",
        "//cmd/beacon-chain/flags:go_default_library",
        "//config/features:go_default_library",
+        "//config/fieldparams:go_default_library",
+        "//config/params:go_default_library",
        "//crypto/bls:go_default_library",
+        "//encoding/bytesutil:go_default_library",
        "//monitoring/tracing:go_default_library",
+        "//proto/engine/v1:go_default_library",
        "//proto/eth/v1:go_default_library",
        "//proto/prysm/v1alpha1:go_default_library",
        "//proto/prysm/v1alpha1/attestation:go_default_library",
        "//proto/prysm/v1alpha1/block:go_default_library",
        "//runtime/version:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "//shared/params:go_default_library",
        "//time:go_default_library",
        "//time/slots:go_default_library",
-        "@com_github_emicklei_dot//:go_default_library",
+        "@com_github_ethereum_go_ethereum//common:go_default_library",
+        "@com_github_ethereum_go_ethereum//common/hexutil:go_default_library",
+        "@com_github_holiman_uint256//:go_default_library",
        "@com_github_pkg_errors//:go_default_library",
        "@com_github_prometheus_client_golang//prometheus:go_default_library",
        "@com_github_prometheus_client_golang//prometheus/promauto:go_default_library",
@@ -86,10 +103,13 @@ go_test(
        "checktags_test.go",
        "head_sync_committee_info_test.go",
        "head_test.go",
-        "info_test.go",
        "init_test.go",
        "log_test.go",
        "metrics_test.go",
+        "mock_engine_test.go",
+        "mock_test.go",
+        "optimistic_sync_test.go",
+        "pow_block_test.go",
        "process_attestation_test.go",
        "process_block_test.go",
        "receive_attestation_test.go",
@@ -112,13 +132,14 @@ go_test(
        "//beacon-chain/powchain:go_default_library",
        "//beacon-chain/state/stateutil:go_default_library",
        "//beacon-chain/state/v1:go_default_library",
+        "//config/fieldparams:go_default_library",
+        "//config/params:go_default_library",
+        "//encoding/bytesutil:go_default_library",
        "//proto/prysm/v1alpha1:go_default_library",
        "//proto/prysm/v1alpha1/wrapper:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "//shared/params:go_default_library",
-        "//shared/testutil:go_default_library",
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
+        "//testing/util:go_default_library",
        "@com_github_ethereum_go_ethereum//:go_default_library",
        "@com_github_ethereum_go_ethereum//common:go_default_library",
        "@com_github_ethereum_go_ethereum//core/types:go_default_library",
@@ -136,6 +157,7 @@ go_test(
        "chain_info_norace_test.go",
        "checktags_test.go",
        "init_test.go",
+        "mock_test.go",
        "receive_block_test.go",
        "service_norace_test.go",
    ],
@@ -161,13 +183,13 @@ go_test(
        "//beacon-chain/db/testing:go_default_library",
        "//beacon-chain/p2p:go_default_library",
        "//beacon-chain/powchain:go_default_library",
+        "//config/params:go_default_library",
+        "//encoding/bytesutil:go_default_library",
        "//proto/prysm/v1alpha1:go_default_library",
        "//proto/prysm/v1alpha1/wrapper:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "//shared/params:go_default_library",
-        "//shared/testutil:go_default_library",
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
+        "//testing/util:go_default_library",
        "@com_github_ethereum_go_ethereum//:go_default_library",
        "@com_github_ethereum_go_ethereum//common:go_default_library",
        "@com_github_ethereum_go_ethereum//core/types:go_default_library",
--- a/beacon-chain/blockchain/chain_info.go
+++ b/beacon-chain/blockchain/chain_info.go
@@ -6,12 +6,14 @@ import (

 	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
-	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	"go.opencensus.io/trace"
 )

@@ -35,7 +37,7 @@ type TimeFetcher interface {

 // GenesisFetcher retrieves the Ethereum consensus data related to its genesis.
 type GenesisFetcher interface {
-	GenesisValidatorRoot() [32]byte
+	GenesisValidatorsRoot() [32]byte
 }

 // HeadFetcher defines a common interface for methods in blockchain service which
@@ -47,14 +49,16 @@ type HeadFetcher interface {
 	HeadState(ctx context.Context) (state.BeaconState, error)
 	HeadValidatorsIndices(ctx context.Context, epoch types.Epoch) ([]types.ValidatorIndex, error)
 	HeadSeed(ctx context.Context, epoch types.Epoch) ([32]byte, error)
-	HeadGenesisValidatorRoot() [32]byte
+	HeadGenesisValidatorsRoot() [32]byte
 	HeadETH1Data() *ethpb.Eth1Data
-	HeadPublicKeyToValidatorIndex(ctx context.Context, pubKey [48]byte) (types.ValidatorIndex, bool)
-	HeadValidatorIndexToPublicKey(ctx context.Context, index types.ValidatorIndex) ([48]byte, error)
-	ProtoArrayStore() *protoarray.Store
+	HeadPublicKeyToValidatorIndex(pubKey [fieldparams.BLSPubkeyLength]byte) (types.ValidatorIndex, bool)
+	HeadValidatorIndexToPublicKey(ctx context.Context, index types.ValidatorIndex) ([fieldparams.BLSPubkeyLength]byte, error)
 	ChainHeads() ([][32]byte, []types.Slot)
+	IsOptimistic(ctx context.Context) (bool, error)
+	IsOptimisticForRoot(ctx context.Context, root [32]byte) (bool, error)
 	HeadSyncCommitteeFetcher
 	HeadDomainFetcher
+	ForkChoicer() forkchoice.ForkChoicer
 }

 // ForkFetcher retrieves the current fork information of the Ethereum beacon chain.
@@ -76,31 +80,45 @@ type FinalizationFetcher interface {
 	PreviousJustifiedCheckpt() *ethpb.Checkpoint
 }

-// FinalizedCheckpt returns the latest finalized checkpoint from head state.
+// FinalizedCheckpt returns the latest finalized checkpoint from chain store.
 func (s *Service) FinalizedCheckpt() *ethpb.Checkpoint {
-	if s.finalizedCheckpt == nil {
+	cp := s.store.FinalizedCheckpt()
+	if cp == nil {
 		return &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}
 	}

-	return ethpb.CopyCheckpoint(s.finalizedCheckpt)
+	return ethpb.CopyCheckpoint(cp)
 }

-// CurrentJustifiedCheckpt returns the current justified checkpoint from head state.
+// CurrentJustifiedCheckpt returns the current justified checkpoint from chain store.
 func (s *Service) CurrentJustifiedCheckpt() *ethpb.Checkpoint {
-	if s.justifiedCheckpt == nil {
+	cp := s.store.JustifiedCheckpt()
+	if cp == nil {
 		return &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}
 	}

-	return ethpb.CopyCheckpoint(s.justifiedCheckpt)
+	return ethpb.CopyCheckpoint(cp)
 }

-// PreviousJustifiedCheckpt returns the previous justified checkpoint from head state.
+// PreviousJustifiedCheckpt returns the previous justified checkpoint from chain store.
 func (s *Service) PreviousJustifiedCheckpt() *ethpb.Checkpoint {
-	if s.prevJustifiedCheckpt == nil {
+	cp := s.store.PrevJustifiedCheckpt()
+	if cp == nil {
 		return &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}
 	}

-	return ethpb.CopyCheckpoint(s.prevJustifiedCheckpt)
+	return ethpb.CopyCheckpoint(cp)
+}
+
+// BestJustifiedCheckpt returns the best justified checkpoint from store.
+func (s *Service) BestJustifiedCheckpt() *ethpb.Checkpoint {
+	cp := s.store.BestJustifiedCheckpt()
+	// If there is no best justified checkpoint, return the checkpoint with root as zeros to be used for genesis cases.
+	if cp == nil {
+		return &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}
+	}
+
+	return ethpb.CopyCheckpoint(cp)
 }

 // HeadSlot returns the slot of the head of the chain.
@@ -182,7 +200,7 @@ func (s *Service) HeadValidatorsIndices(ctx context.Context, epoch types.Epoch)
 	if !s.hasHeadState() {
 		return []types.ValidatorIndex{}, nil
 	}
-	return helpers.ActiveValidatorIndices(s.headState(ctx), epoch)
+	return helpers.ActiveValidatorIndices(ctx, s.headState(ctx), epoch)
 }

 // HeadSeed returns the seed from the head view of a given epoch.
@@ -197,8 +215,8 @@ func (s *Service) HeadSeed(ctx context.Context, epoch types.Epoch) ([32]byte, er
 	return helpers.Seed(s.headState(ctx), epoch, params.BeaconConfig().DomainBeaconAttester)
 }

-// HeadGenesisValidatorRoot returns genesis validator root of the head state.
-func (s *Service) HeadGenesisValidatorRoot() [32]byte {
+// HeadGenesisValidatorsRoot returns genesis validators root of the head state.
+func (s *Service) HeadGenesisValidatorsRoot() [32]byte {
 	s.headLock.RLock()
 	defer s.headLock.RUnlock()

@@ -206,7 +224,7 @@ func (s *Service) HeadGenesisValidatorRoot() [32]byte {
 		return [32]byte{}
 	}

-	return s.headGenesisValidatorRoot()
+	return s.headGenesisValidatorsRoot()
 }

 // HeadETH1Data returns the eth1data of the current head state.
@@ -220,26 +238,21 @@ func (s *Service) HeadETH1Data() *ethpb.Eth1Data {
 	return s.head.state.Eth1Data()
 }

-// ProtoArrayStore returns the proto array store object.
-func (s *Service) ProtoArrayStore() *protoarray.Store {
-	return s.cfg.ForkChoiceStore.Store()
-}
-
 // GenesisTime returns the genesis time of beacon chain.
 func (s *Service) GenesisTime() time.Time {
 	return s.genesisTime
 }

-// GenesisValidatorRoot returns the genesis validator
+// GenesisValidatorsRoot returns the genesis validator
 // root of the chain.
-func (s *Service) GenesisValidatorRoot() [32]byte {
+func (s *Service) GenesisValidatorsRoot() [32]byte {
 	s.headLock.RLock()
 	defer s.headLock.RUnlock()

 	if !s.hasHeadState() {
 		return [32]byte{}
 	}
-	return bytesutil.ToBytes32(s.head.state.GenesisValidatorRoot())
+	return bytesutil.ToBytes32(s.head.state.GenesisValidatorsRoot())
 }

 // CurrentFork retrieves the latest fork information of the beacon chain.
@@ -270,41 +283,61 @@ func (s *Service) IsCanonical(ctx context.Context, blockRoot [32]byte) (bool, er
 // ChainHeads returns all possible chain heads (leaves of fork choice tree).
 // Heads roots and heads slots are returned.
 func (s *Service) ChainHeads() ([][32]byte, []types.Slot) {
-	nodes := s.ProtoArrayStore().Nodes()
-
-	// Deliberate choice to not preallocate space for below.
-	// Heads cant be more than 2-3 in the worst case where pre-allocation will be 64 to begin with.
-	headsRoots := make([][32]byte, 0)
-	headsSlots := make([]types.Slot, 0)
-
-	nonExistentNode := ^uint64(0)
-	for _, node := range nodes {
-		// Possible heads have no children.
-		if node.BestDescendant() == nonExistentNode && node.BestChild() == nonExistentNode {
-			headsRoots = append(headsRoots, node.Root())
-			headsSlots = append(headsSlots, node.Slot())
-		}
-	}
-
-	return headsRoots, headsSlots
+	return s.cfg.ForkChoiceStore.Tips()
 }

 // HeadPublicKeyToValidatorIndex returns the validator index of the `pubkey` in current head state.
-func (s *Service) HeadPublicKeyToValidatorIndex(ctx context.Context, pubKey [48]byte) (types.ValidatorIndex, bool) {
+func (s *Service) HeadPublicKeyToValidatorIndex(pubKey [fieldparams.BLSPubkeyLength]byte) (types.ValidatorIndex, bool) {
 	s.headLock.RLock()
 	defer s.headLock.RUnlock()
-
-	return s.headState(ctx).ValidatorIndexByPubkey(pubKey)
+	if !s.hasHeadState() {
+		return 0, false
+	}
+	return s.headValidatorIndexAtPubkey(pubKey)
 }

 // HeadValidatorIndexToPublicKey returns the pubkey of the validator `index`  in current head state.
-func (s *Service) HeadValidatorIndexToPublicKey(ctx context.Context, index types.ValidatorIndex) ([48]byte, error) {
+func (s *Service) HeadValidatorIndexToPublicKey(_ context.Context, index types.ValidatorIndex) ([fieldparams.BLSPubkeyLength]byte, error) {
 	s.headLock.RLock()
 	defer s.headLock.RUnlock()
-
+	if !s.hasHeadState() {
+		return [fieldparams.BLSPubkeyLength]byte{}, nil
+	}
 	v, err := s.headValidatorAtIndex(index)
 	if err != nil {
-		return [48]byte{}, err
+		return [fieldparams.BLSPubkeyLength]byte{}, err
 	}
 	return v.PublicKey(), nil
 }
+
+// ForkChoicer returns the forkchoice interface
+func (s *Service) ForkChoicer() forkchoice.ForkChoicer {
+	return s.cfg.ForkChoiceStore
+}
+
+// IsOptimistic returns true if the current head is optimistic.
+func (s *Service) IsOptimistic(ctx context.Context) (bool, error) {
+	s.headLock.RLock()
+	defer s.headLock.RUnlock()
+	if slots.ToEpoch(s.CurrentSlot()) < params.BeaconConfig().BellatrixForkEpoch {
+		return false, nil
+	}
+
+	return s.cfg.ForkChoiceStore.IsOptimistic(ctx, s.head.root)
+}
+
+// IsOptimisticForRoot takes the root and slot as aguments instead of the current head
+// and returns true if it is optimistic.
+func (s *Service) IsOptimisticForRoot(ctx context.Context, root [32]byte) (bool, error) {
+	return s.cfg.ForkChoiceStore.IsOptimistic(ctx, root)
+}
+
+// SetGenesisTime sets the genesis time of beacon chain.
+func (s *Service) SetGenesisTime(t time.Time) {
+	s.genesisTime = t
+}
+
+// ForkChoiceStore returns the fork choice store in the service
+func (s *Service) ForkChoiceStore() forkchoice.ForkChoicer {
+	return s.cfg.ForkChoiceStore
+}
--- a/beacon-chain/blockchain/chain_info_norace_test.go
+++ b/beacon-chain/blockchain/chain_info_norace_test.go
@@ -8,13 +8,13 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 func TestHeadSlot_DataRace(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg: &Config{BeaconDB: beaconDB},
+		cfg: &config{BeaconDB: beaconDB},
 	}
 	go func() {
 		require.NoError(t, s.saveHead(context.Background(), [32]byte{}))
@@ -25,7 +25,7 @@ func TestHeadSlot_DataRace(t *testing.T) {
 func TestHeadRoot_DataRace(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg:  &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
+		cfg:  &config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
 		head: &head{root: [32]byte{'A'}},
 	}
 	go func() {
@@ -38,7 +38,7 @@ func TestHeadRoot_DataRace(t *testing.T) {
 func TestHeadBlock_DataRace(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg:  &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
+		cfg:  &config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
 		head: &head{block: wrapper.WrappedPhase0SignedBeaconBlock(&ethpb.SignedBeaconBlock{})},
 	}
 	go func() {
@@ -51,7 +51,7 @@ func TestHeadBlock_DataRace(t *testing.T) {
 func TestHeadState_DataRace(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg: &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
+		cfg: &config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
 	}
 	go func() {
 		require.NoError(t, s.saveHead(context.Background(), [32]byte{}))
--- a/beacon-chain/blockchain/chain_info_test.go
+++ b/beacon-chain/blockchain/chain_info_test.go
@@ -8,15 +8,17 @@ import (
 	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	doublylinkedtree "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/doubly-linked-tree"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	v1 "github.com/prysmaticlabs/prysm/beacon-chain/state/v1"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
 	"google.golang.org/protobuf/proto"
 )

@@ -39,12 +41,18 @@ func TestHeadRoot_Nil(t *testing.T) {
 	assert.DeepEqual(t, params.BeaconConfig().ZeroHash[:], headRoot, "Incorrect pre chain start value")
 }

+func TestService_ForkChoiceStore(t *testing.T) {
+	c := &Service{cfg: &config{ForkChoiceStore: doublylinkedtree.New(0, 0)}}
+	p := c.ForkChoiceStore()
+	require.Equal(t, 0, int(p.FinalizedEpoch()))
+}
+
 func TestFinalizedCheckpt_CanRetrieve(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)

 	cp := &ethpb.Checkpoint{Epoch: 5, Root: bytesutil.PadTo([]byte("foo"), 32)}
 	c := setupBeaconChain(t, beaconDB)
-	c.finalizedCheckpt = cp
+	c.store.SetFinalizedCheckpt(cp)

 	assert.Equal(t, cp.Epoch, c.FinalizedCheckpt().Epoch, "Unexpected finalized epoch")
 }
@@ -55,9 +63,9 @@ func TestFinalizedCheckpt_GenesisRootOk(t *testing.T) {
 	genesisRoot := [32]byte{'A'}
 	cp := &ethpb.Checkpoint{Root: genesisRoot[:]}
 	c := setupBeaconChain(t, beaconDB)
-	c.finalizedCheckpt = cp
-	c.genesisRoot = genesisRoot
-	assert.DeepEqual(t, c.genesisRoot[:], c.FinalizedCheckpt().Root)
+	c.store.SetFinalizedCheckpt(cp)
+	c.originBlockRoot = genesisRoot
+	assert.DeepEqual(t, c.originBlockRoot[:], c.FinalizedCheckpt().Root)
 }

 func TestCurrentJustifiedCheckpt_CanRetrieve(t *testing.T) {
@@ -66,7 +74,7 @@ func TestCurrentJustifiedCheckpt_CanRetrieve(t *testing.T) {
 	c := setupBeaconChain(t, beaconDB)
 	assert.Equal(t, params.BeaconConfig().ZeroHash, bytesutil.ToBytes32(c.CurrentJustifiedCheckpt().Root), "Unexpected justified epoch")
 	cp := &ethpb.Checkpoint{Epoch: 6, Root: bytesutil.PadTo([]byte("foo"), 32)}
-	c.justifiedCheckpt = cp
+	c.store.SetJustifiedCheckpt(cp)
 	assert.Equal(t, cp.Epoch, c.CurrentJustifiedCheckpt().Epoch, "Unexpected justified epoch")
 }

@@ -76,9 +84,9 @@ func TestJustifiedCheckpt_GenesisRootOk(t *testing.T) {
 	c := setupBeaconChain(t, beaconDB)
 	genesisRoot := [32]byte{'B'}
 	cp := &ethpb.Checkpoint{Root: genesisRoot[:]}
-	c.justifiedCheckpt = cp
-	c.genesisRoot = genesisRoot
-	assert.DeepEqual(t, c.genesisRoot[:], c.CurrentJustifiedCheckpt().Root)
+	c.store.SetJustifiedCheckpt(cp)
+	c.originBlockRoot = genesisRoot
+	assert.DeepEqual(t, c.originBlockRoot[:], c.CurrentJustifiedCheckpt().Root)
 }

 func TestPreviousJustifiedCheckpt_CanRetrieve(t *testing.T) {
@@ -87,7 +95,7 @@ func TestPreviousJustifiedCheckpt_CanRetrieve(t *testing.T) {
 	cp := &ethpb.Checkpoint{Epoch: 7, Root: bytesutil.PadTo([]byte("foo"), 32)}
 	c := setupBeaconChain(t, beaconDB)
 	assert.Equal(t, params.BeaconConfig().ZeroHash, bytesutil.ToBytes32(c.CurrentJustifiedCheckpt().Root), "Unexpected justified epoch")
-	c.prevJustifiedCheckpt = cp
+	c.store.SetPrevJustifiedCheckpt(cp)
 	assert.Equal(t, cp.Epoch, c.PreviousJustifiedCheckpt().Epoch, "Unexpected previous justified epoch")
 }

@@ -97,9 +105,9 @@ func TestPrevJustifiedCheckpt_GenesisRootOk(t *testing.T) {
 	genesisRoot := [32]byte{'C'}
 	cp := &ethpb.Checkpoint{Root: genesisRoot[:]}
 	c := setupBeaconChain(t, beaconDB)
-	c.prevJustifiedCheckpt = cp
-	c.genesisRoot = genesisRoot
-	assert.DeepEqual(t, c.genesisRoot[:], c.PreviousJustifiedCheckpt().Root)
+	c.store.SetPrevJustifiedCheckpt(cp)
+	c.originBlockRoot = genesisRoot
+	assert.DeepEqual(t, c.originBlockRoot[:], c.PreviousJustifiedCheckpt().Root)
 }

 func TestHeadSlot_CanRetrieve(t *testing.T) {
@@ -120,9 +128,9 @@ func TestHeadRoot_CanRetrieve(t *testing.T) {

 func TestHeadRoot_UseDB(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
-	c := &Service{cfg: &Config{BeaconDB: beaconDB}}
+	c := &Service{cfg: &config{BeaconDB: beaconDB}}
 	c.head = &head{root: params.BeaconConfig().ZeroHash}
-	b := testutil.NewBeaconBlock()
+	b := util.NewBeaconBlock()
 	br, err := b.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveBlock(context.Background(), wrapper.WrappedPhase0SignedBeaconBlock(b)))
@@ -134,7 +142,7 @@ func TestHeadRoot_UseDB(t *testing.T) {
 }

 func TestHeadBlock_CanRetrieve(t *testing.T) {
-	b := testutil.NewBeaconBlock()
+	b := util.NewBeaconBlock()
 	b.Block.Slot = 1
 	s, err := v1.InitializeFromProto(&ethpb.BeaconState{})
 	require.NoError(t, err)
@@ -184,15 +192,15 @@ func TestCurrentFork_NilHeadSTate(t *testing.T) {
 	}
 }

-func TestGenesisValidatorRoot_CanRetrieve(t *testing.T) {
+func TestGenesisValidatorsRoot_CanRetrieve(t *testing.T) {
 	// Should not panic if head state is nil.
 	c := &Service{}
-	assert.Equal(t, [32]byte{}, c.GenesisValidatorRoot(), "Did not get correct genesis validator root")
+	assert.Equal(t, [32]byte{}, c.GenesisValidatorsRoot(), "Did not get correct genesis validators root")

 	s, err := v1.InitializeFromProto(&ethpb.BeaconState{GenesisValidatorsRoot: []byte{'a'}})
 	require.NoError(t, err)
 	c.head = &head{state: s}
-	assert.Equal(t, [32]byte{'a'}, c.GenesisValidatorRoot(), "Did not get correct genesis validator root")
+	assert.Equal(t, [32]byte{'a'}, c.GenesisValidatorsRoot(), "Did not get correct genesis validators root")
 }

 func TestHeadETH1Data_Nil(t *testing.T) {
@@ -217,7 +225,7 @@ func TestIsCanonical_Ok(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	c := setupBeaconChain(t, beaconDB)

-	blk := testutil.NewBeaconBlock()
+	blk := util.NewBeaconBlock()
 	blk.Block.Slot = 0
 	root, err := blk.Block.HashTreeRoot()
 	require.NoError(t, err)
@@ -233,7 +241,7 @@ func TestIsCanonical_Ok(t *testing.T) {
 }

 func TestService_HeadValidatorsIndices(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisState(t, 10)
+	s, _ := util.DeterministicGenesisState(t, 10)
 	c := &Service{}

 	c.head = &head{}
@@ -248,7 +256,7 @@ func TestService_HeadValidatorsIndices(t *testing.T) {
 }

 func TestService_HeadSeed(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisState(t, 1)
+	s, _ := util.DeterministicGenesisState(t, 1)
 	c := &Service{}
 	seed, err := helpers.Seed(s, 0, params.BeaconConfig().DomainBeaconAttester)
 	require.NoError(t, err)
@@ -264,57 +272,84 @@ func TestService_HeadSeed(t *testing.T) {
 	require.DeepEqual(t, seed, root)
 }

-func TestService_HeadGenesisValidatorRoot(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisState(t, 1)
+func TestService_HeadGenesisValidatorsRoot(t *testing.T) {
+	s, _ := util.DeterministicGenesisState(t, 1)
 	c := &Service{}

 	c.head = &head{}
-	root := c.HeadGenesisValidatorRoot()
+	root := c.HeadGenesisValidatorsRoot()
 	require.Equal(t, [32]byte{}, root)

 	c.head = &head{state: s}
-	root = c.HeadGenesisValidatorRoot()
-	require.DeepEqual(t, root[:], s.GenesisValidatorRoot())
+	root = c.HeadGenesisValidatorsRoot()
+	require.DeepEqual(t, root[:], s.GenesisValidatorsRoot())
 }
-
-func TestService_ProtoArrayStore(t *testing.T) {
-	c := &Service{cfg: &Config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}}
-	p := c.ProtoArrayStore()
-	require.Equal(t, 0, int(p.FinalizedEpoch()))
-}
-
-func TestService_ChainHeads(t *testing.T) {
+func TestService_ChainHeads_ProtoArray(t *testing.T) {
 	ctx := context.Background()
-	c := &Service{cfg: &Config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}}
-	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, [32]byte{}, 0, 0))
-	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, [32]byte{}, 0, 0))
-	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 102, [32]byte{'c'}, [32]byte{'b'}, [32]byte{}, 0, 0))
-	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 103, [32]byte{'d'}, [32]byte{}, [32]byte{}, 0, 0))
-	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 104, [32]byte{'e'}, [32]byte{'b'}, [32]byte{}, 0, 0))
+	c := &Service{cfg: &config{ForkChoiceStore: protoarray.New(0, 0,
+		params.BeaconConfig().ZeroHash)}}
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 102, [32]byte{'c'}, [32]byte{'b'}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 103, [32]byte{'d'}, [32]byte{}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 104, [32]byte{'e'}, [32]byte{'b'}, 0, 0, false))

 	roots, slots := c.ChainHeads()
 	require.DeepEqual(t, [][32]byte{{'c'}, {'d'}, {'e'}}, roots)
 	require.DeepEqual(t, []types.Slot{102, 103, 104}, slots)
 }

+func TestService_ChainHeads_DoublyLinkedTree(t *testing.T) {
+	ctx := context.Background()
+	c := &Service{cfg: &config{ForkChoiceStore: doublylinkedtree.New(0, 0)}}
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 102, [32]byte{'c'}, [32]byte{'b'}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 103, [32]byte{'d'}, [32]byte{}, 0, 0, false))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 104, [32]byte{'e'}, [32]byte{'b'}, 0, 0, false))
+
+	roots, slots := c.ChainHeads()
+	require.Equal(t, 3, len(roots))
+	rootMap := map[[32]byte]types.Slot{[32]byte{'c'}: 102, [32]byte{'d'}: 103, [32]byte{'e'}: 104}
+	for i, root := range roots {
+		slot, ok := rootMap[root]
+		require.Equal(t, true, ok)
+		require.Equal(t, slot, slots[i])
+	}
+}
+
 func TestService_HeadPublicKeyToValidatorIndex(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisState(t, 10)
+	s, _ := util.DeterministicGenesisState(t, 10)
 	c := &Service{}
 	c.head = &head{state: s}

-	_, e := c.HeadPublicKeyToValidatorIndex(context.Background(), [48]byte{})
+	_, e := c.HeadPublicKeyToValidatorIndex([fieldparams.BLSPubkeyLength]byte{})
 	require.Equal(t, false, e)

 	v, err := s.ValidatorAtIndex(0)
 	require.NoError(t, err)

-	i, e := c.HeadPublicKeyToValidatorIndex(context.Background(), bytesutil.ToBytes48(v.PublicKey))
+	i, e := c.HeadPublicKeyToValidatorIndex(bytesutil.ToBytes48(v.PublicKey))
 	require.Equal(t, true, e)
 	require.Equal(t, types.ValidatorIndex(0), i)
 }

+func TestService_HeadPublicKeyToValidatorIndexNil(t *testing.T) {
+	c := &Service{}
+	c.head = nil
+
+	idx, e := c.HeadPublicKeyToValidatorIndex([fieldparams.BLSPubkeyLength]byte{})
+	require.Equal(t, false, e)
+	require.Equal(t, types.ValidatorIndex(0), idx)
+
+	c.head = &head{state: nil}
+	i, e := c.HeadPublicKeyToValidatorIndex([fieldparams.BLSPubkeyLength]byte{})
+	require.Equal(t, false, e)
+	require.Equal(t, types.ValidatorIndex(0), i)
+}
+
 func TestService_HeadValidatorIndexToPublicKey(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisState(t, 10)
+	s, _ := util.DeterministicGenesisState(t, 10)
 	c := &Service{}
 	c.head = &head{state: s}

@@ -326,3 +361,79 @@ func TestService_HeadValidatorIndexToPublicKey(t *testing.T) {

 	require.Equal(t, bytesutil.ToBytes48(v.PublicKey), p)
 }
+
+func TestService_HeadValidatorIndexToPublicKeyNil(t *testing.T) {
+	c := &Service{}
+	c.head = nil
+
+	p, err := c.HeadValidatorIndexToPublicKey(context.Background(), 0)
+	require.NoError(t, err)
+	require.Equal(t, [fieldparams.BLSPubkeyLength]byte{}, p)
+
+	c.head = &head{state: nil}
+	p, err = c.HeadValidatorIndexToPublicKey(context.Background(), 0)
+	require.NoError(t, err)
+	require.Equal(t, [fieldparams.BLSPubkeyLength]byte{}, p)
+}
+
+func TestService_IsOptimistic_ProtoArray(t *testing.T) {
+	params.SetupTestConfigCleanup(t)
+	cfg := params.BeaconConfig()
+	cfg.BellatrixForkEpoch = 0
+	params.OverrideBeaconConfig(cfg)
+
+	ctx := context.Background()
+	c := &Service{cfg: &config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}, head: &head{slot: 101, root: [32]byte{'b'}}}
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, 0, 0, true))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, 0, 0, true))
+
+	opt, err := c.IsOptimistic(ctx)
+	require.NoError(t, err)
+	require.Equal(t, true, opt)
+}
+
+func TestService_IsOptimistic_DoublyLinkedTree(t *testing.T) {
+	params.SetupTestConfigCleanup(t)
+	cfg := params.BeaconConfig()
+	cfg.BellatrixForkEpoch = 0
+	params.OverrideBeaconConfig(cfg)
+
+	ctx := context.Background()
+	c := &Service{cfg: &config{ForkChoiceStore: doublylinkedtree.New(0, 0)}, head: &head{slot: 101, root: [32]byte{'b'}}}
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, 0, 0, true))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, 0, 0, true))
+
+	opt, err := c.IsOptimistic(ctx)
+	require.NoError(t, err)
+	require.Equal(t, true, opt)
+}
+
+func TestService_IsOptimisticBeforeBellatrix(t *testing.T) {
+	ctx := context.Background()
+	c := &Service{genesisTime: time.Now()}
+	opt, err := c.IsOptimistic(ctx)
+	require.NoError(t, err)
+	require.Equal(t, false, opt)
+}
+
+func TestService_IsOptimisticForRoot_ProtoArray(t *testing.T) {
+	ctx := context.Background()
+	c := &Service{cfg: &config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}, head: &head{slot: 101, root: [32]byte{'b'}}}
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, 0, 0, true))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, 0, 0, true))
+
+	opt, err := c.IsOptimisticForRoot(ctx, [32]byte{'a'})
+	require.NoError(t, err)
+	require.Equal(t, true, opt)
+}
+
+func TestService_IsOptimisticForRoot_DoublyLinkedTree(t *testing.T) {
+	ctx := context.Background()
+	c := &Service{cfg: &config{ForkChoiceStore: doublylinkedtree.New(0, 0)}, head: &head{slot: 101, root: [32]byte{'b'}}}
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 100, [32]byte{'a'}, [32]byte{}, 0, 0, true))
+	require.NoError(t, c.cfg.ForkChoiceStore.ProcessBlock(ctx, 101, [32]byte{'b'}, [32]byte{'a'}, 0, 0, true))
+
+	opt, err := c.IsOptimisticForRoot(ctx, [32]byte{'a'})
+	require.NoError(t, err)
+	require.Equal(t, true, opt)
+}
--- a/beacon-chain/blockchain/error.go
+++ b/beacon-chain/blockchain/error.go
@@ -0,0 +1,12 @@
+package blockchain
+
+import "github.com/pkg/errors"
+
+var (
+	// errNilJustifiedInStore is returned when a nil justified checkpt is returned from store.
+	errNilJustifiedInStore = errors.New("nil justified checkpoint returned from store")
+	// errNilBestJustifiedInStore is returned when a nil justified checkpt is returned from store.
+	errNilBestJustifiedInStore = errors.New("nil best justified checkpoint returned from store")
+	// errNilFinalizedInStore is returned when a nil finalized checkpt is returned from store.
+	errNilFinalizedInStore = errors.New("nil finalized checkpoint returned from store")
+)
--- a/beacon-chain/blockchain/head.go
+++ b/beacon-chain/blockchain/head.go
@@ -7,22 +7,38 @@ import (

 	"github.com/pkg/errors"
 	types "github.com/prysmaticlabs/eth2-types"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/feed"
 	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	doublylinkedtree "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/doubly-linked-tree"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
 	"github.com/prysmaticlabs/prysm/config/features"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpbv1 "github.com/prysmaticlabs/prysm/proto/eth/v1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
 	"github.com/prysmaticlabs/prysm/time/slots"
 	"github.com/sirupsen/logrus"
 	"go.opencensus.io/trace"
 )

+// UpdateHeadWithBalances updates the beacon state head after getting justified balanced from cache.
+func (s *Service) UpdateHeadWithBalances(ctx context.Context) error {
+	cp := s.store.JustifiedCheckpt()
+	if cp == nil {
+		return errors.New("no justified checkpoint")
+	}
+	balances, err := s.justifiedBalances.get(ctx, bytesutil.ToBytes32(cp.Root))
+	if err != nil {
+		msg := fmt.Sprintf("could not read balances for state w/ justified checkpoint %#x", cp.Root)
+		return errors.Wrap(err, msg)
+	}
+
+	return s.updateHead(ctx, balances)
+}
+
 // This defines the current chain service's view of head.
 type head struct {
 	slot  types.Slot              // current head slot.
@@ -37,24 +53,20 @@ func (s *Service) updateHead(ctx context.Context, balances []uint64) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.updateHead")
 	defer span.End()

-	// To get the proper head update, a node first checks its best justified
-	// can become justified. This is designed to prevent bounce attack and
-	// ensure head gets its best justified info.
-	if s.bestJustifiedCheckpt.Epoch > s.justifiedCheckpt.Epoch {
-		s.justifiedCheckpt = s.bestJustifiedCheckpt
-		if err := s.cacheJustifiedStateBalances(ctx, bytesutil.ToBytes32(s.justifiedCheckpt.Root)); err != nil {
-			return err
-		}
-	}
-
 	// Get head from the fork choice service.
-	f := s.finalizedCheckpt
-	j := s.justifiedCheckpt
-	// To get head before the first justified epoch, the fork choice will start with genesis root
+	f := s.store.FinalizedCheckpt()
+	if f == nil {
+		return errNilFinalizedInStore
+	}
+	j := s.store.JustifiedCheckpt()
+	if j == nil {
+		return errNilJustifiedInStore
+	}
+	// To get head before the first justified epoch, the fork choice will start with origin root
 	// instead of zero hashes.
 	headStartRoot := bytesutil.ToBytes32(j.Root)
 	if headStartRoot == params.BeaconConfig().ZeroHash {
-		headStartRoot = s.genesisRoot
+		headStartRoot = s.originBlockRoot
 	}

 	// In order to process head, fork choice store requires justified info.
@@ -66,8 +78,13 @@ func (s *Service) updateHead(ctx context.Context, balances []uint64) error {
 		if err != nil {
 			return err
 		}
-		s.cfg.ForkChoiceStore = protoarray.New(j.Epoch, f.Epoch, bytesutil.ToBytes32(f.Root))
-		if err := s.insertBlockToForkChoiceStore(ctx, jb.Block(), headStartRoot, f, j); err != nil {
+		if features.Get().EnableForkChoiceDoublyLinkedTree {
+			s.cfg.ForkChoiceStore = doublylinkedtree.New(j.Epoch, f.Epoch)
+		} else {
+			s.cfg.ForkChoiceStore = protoarray.New(j.Epoch, f.Epoch, bytesutil.ToBytes32(f.Root))
+		}
+		// TODO(10261) send optimistic status
+		if err := s.insertBlockToForkChoiceStore(ctx, jb.Block(), headStartRoot, f, j, false /* optimistic status */); err != nil {
 			return err
 		}
 	}
@@ -107,8 +124,8 @@ func (s *Service) saveHead(ctx context.Context, headRoot [32]byte) error {
 	if err != nil {
 		return err
 	}
-	if newHeadBlock == nil || newHeadBlock.IsNil() || newHeadBlock.Block().IsNil() {
-		return errors.New("cannot save nil head block")
+	if err := helpers.BeaconBlockIsNil(newHeadBlock); err != nil {
+		return err
 	}

 	// Get the new head state from cached state or DB.
@@ -141,7 +158,7 @@ func (s *Service) saveHead(ctx context.Context, headRoot [32]byte) error {
 				NewHeadBlock: headRoot[:],
 				OldHeadState: oldStateRoot,
 				NewHeadState: newStateRoot,
-				Epoch:        core.SlotToEpoch(newHeadSlot),
+				Epoch:        slots.ToEpoch(newHeadSlot),
 			},
 		})

@@ -175,7 +192,7 @@ func (s *Service) saveHead(ctx context.Context, headRoot [32]byte) error {
 // root in DB. With the inception of initial-sync-cache-state flag, it uses finalized
 // check point as anchors to resume sync therefore head is no longer needed to be saved on per slot basis.
 func (s *Service) saveHeadNoDB(ctx context.Context, b block.SignedBeaconBlock, r [32]byte, hs state.BeaconState) error {
-	if err := helpers.VerifyNilBeaconBlock(b); err != nil {
+	if err := helpers.BeaconBlockIsNil(b); err != nil {
 		return err
 	}
 	cachedHeadRoot, err := s.HeadRoot(ctx)
@@ -248,16 +265,16 @@ func (s *Service) headBlock() block.SignedBeaconBlock {
 // It does a full copy on head state for immutability.
 // This is a lock free version.
 func (s *Service) headState(ctx context.Context) state.BeaconState {
-	ctx, span := trace.StartSpan(ctx, "blockChain.headState")
+	_, span := trace.StartSpan(ctx, "blockChain.headState")
 	defer span.End()

 	return s.head.state.Copy()
 }

-// This returns the genesis validator root of the head state.
+// This returns the genesis validators root of the head state.
 // This is a lock free version.
-func (s *Service) headGenesisValidatorRoot() [32]byte {
-	return bytesutil.ToBytes32(s.head.state.GenesisValidatorRoot())
+func (s *Service) headGenesisValidatorsRoot() [32]byte {
+	return bytesutil.ToBytes32(s.head.state.GenesisValidatorsRoot())
 }

 // This returns the validator referenced by the provided index in
@@ -267,63 +284,19 @@ func (s *Service) headValidatorAtIndex(index types.ValidatorIndex) (state.ReadOn
 	return s.head.state.ValidatorAtIndexReadOnly(index)
 }

+// This returns the validator index referenced by the provided pubkey in
+// the head state.
+// This is a lock free version.
+func (s *Service) headValidatorIndexAtPubkey(pubKey [fieldparams.BLSPubkeyLength]byte) (types.ValidatorIndex, bool) {
+	return s.head.state.ValidatorIndexByPubkey(pubKey)
+}
+
 // Returns true if head state exists.
 // This is the lock free version.
 func (s *Service) hasHeadState() bool {
 	return s.head != nil && s.head.state != nil
 }

-// This caches justified state balances to be used for fork choice.
-func (s *Service) cacheJustifiedStateBalances(ctx context.Context, justifiedRoot [32]byte) error {
-	if err := s.cfg.BeaconDB.SaveBlocks(ctx, s.getInitSyncBlocks()); err != nil {
-		return err
-	}
-
-	s.clearInitSyncBlocks()
-
-	var justifiedState state.BeaconState
-	var err error
-	if justifiedRoot == s.genesisRoot {
-		justifiedState, err = s.cfg.BeaconDB.GenesisState(ctx)
-		if err != nil {
-			return err
-		}
-	} else {
-		justifiedState, err = s.cfg.StateGen.StateByRoot(ctx, justifiedRoot)
-		if err != nil {
-			return err
-		}
-	}
-	if justifiedState == nil || justifiedState.IsNil() {
-		return errors.New("justified state can't be nil")
-	}
-
-	epoch := core.CurrentEpoch(justifiedState)
-
-	justifiedBalances := make([]uint64, justifiedState.NumValidators())
-	if err := justifiedState.ReadFromEveryValidator(func(idx int, val state.ReadOnlyValidator) error {
-		if helpers.IsActiveValidatorUsingTrie(val, epoch) {
-			justifiedBalances[idx] = val.EffectiveBalance()
-		} else {
-			justifiedBalances[idx] = 0
-		}
-		return nil
-	}); err != nil {
-		return err
-	}
-
-	s.justifiedBalancesLock.Lock()
-	defer s.justifiedBalancesLock.Unlock()
-	s.justifiedBalances = justifiedBalances
-	return nil
-}
-
-func (s *Service) getJustifiedBalances() []uint64 {
-	s.justifiedBalancesLock.RLock()
-	defer s.justifiedBalancesLock.RUnlock()
-	return s.justifiedBalances
-}
-
 // Notifies a common event feed of a new chain head event. Called right after a new
 // chain head is determined, set, and saved to disk.
 func (s *Service) notifyNewHeadEvent(
@@ -332,19 +305,19 @@ func (s *Service) notifyNewHeadEvent(
 	newHeadStateRoot,
 	newHeadRoot []byte,
 ) error {
-	previousDutyDependentRoot := s.genesisRoot[:]
-	currentDutyDependentRoot := s.genesisRoot[:]
+	previousDutyDependentRoot := s.originBlockRoot[:]
+	currentDutyDependentRoot := s.originBlockRoot[:]

 	var previousDutyEpoch types.Epoch
-	currentDutyEpoch := core.SlotToEpoch(newHeadSlot)
+	currentDutyEpoch := slots.ToEpoch(newHeadSlot)
 	if currentDutyEpoch > 0 {
 		previousDutyEpoch = currentDutyEpoch.Sub(1)
 	}
-	currentDutySlot, err := core.StartSlot(currentDutyEpoch)
+	currentDutySlot, err := slots.EpochStart(currentDutyEpoch)
 	if err != nil {
 		return errors.Wrap(err, "could not get duty slot")
 	}
-	previousDutySlot, err := core.StartSlot(previousDutyEpoch)
+	previousDutySlot, err := slots.EpochStart(previousDutyEpoch)
 	if err != nil {
 		return errors.Wrap(err, "could not get duty slot")
 	}
@@ -366,7 +339,7 @@ func (s *Service) notifyNewHeadEvent(
 			Slot:                      newHeadSlot,
 			Block:                     newHeadRoot,
 			State:                     newHeadStateRoot,
-			EpochTransition:           core.IsEpochEnd(newHeadSlot),
+			EpochTransition:           slots.IsEpochStart(newHeadSlot),
 			PreviousDutyDependentRoot: previousDutyDependentRoot,
 			CurrentDutyDependentRoot:  currentDutyDependentRoot,
 		},
--- a/beacon-chain/blockchain/head_sync_committee_info.go
+++ b/beacon-chain/blockchain/head_sync_committee_info.go
@@ -8,13 +8,14 @@ import (
 	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/async"
 	"github.com/prysmaticlabs/prysm/beacon-chain/cache"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/altair"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/signing"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/config/params"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/time/slots"
 )

 // Initialize the state cache for sync committees.
@@ -61,14 +62,14 @@ func (s *Service) HeadSyncContributionProofDomain(ctx context.Context, slot type
 // rather than for the range
 // [compute_start_slot_at_epoch(epoch), compute_start_slot_at_epoch(epoch) + SLOTS_PER_EPOCH)
 func (s *Service) HeadSyncCommitteeIndices(ctx context.Context, index types.ValidatorIndex, slot types.Slot) ([]types.CommitteeIndex, error) {
-	nextSlotEpoch := core.SlotToEpoch(slot + 1)
-	currentEpoch := core.SlotToEpoch(slot)
+	nextSlotEpoch := slots.ToEpoch(slot + 1)
+	currentEpoch := slots.ToEpoch(slot)

 	switch {
-	case core.SyncCommitteePeriod(nextSlotEpoch) == core.SyncCommitteePeriod(currentEpoch):
+	case slots.SyncCommitteePeriod(nextSlotEpoch) == slots.SyncCommitteePeriod(currentEpoch):
 		return s.headCurrentSyncCommitteeIndices(ctx, index, slot)
 	// At sync committee period boundary, validator should sample the next epoch sync committee.
-	case core.SyncCommitteePeriod(nextSlotEpoch) == core.SyncCommitteePeriod(currentEpoch)+1:
+	case slots.SyncCommitteePeriod(nextSlotEpoch) == slots.SyncCommitteePeriod(currentEpoch)+1:
 		return s.headNextSyncCommitteeIndices(ctx, index, slot)
 	default:
 		// Impossible condition.
@@ -104,11 +105,11 @@ func (s *Service) HeadSyncCommitteePubKeys(ctx context.Context, slot types.Slot,
 		return nil, err
 	}

-	nextSlotEpoch := core.SlotToEpoch(headState.Slot() + 1)
-	currEpoch := core.SlotToEpoch(headState.Slot())
+	nextSlotEpoch := slots.ToEpoch(headState.Slot() + 1)
+	currEpoch := slots.ToEpoch(headState.Slot())

 	var syncCommittee *ethpb.SyncCommittee
-	if currEpoch == nextSlotEpoch || core.SyncCommitteePeriod(currEpoch) == core.SyncCommitteePeriod(nextSlotEpoch) {
+	if currEpoch == nextSlotEpoch || slots.SyncCommitteePeriod(currEpoch) == slots.SyncCommitteePeriod(nextSlotEpoch) {
 		syncCommittee, err = headState.CurrentSyncCommittee()
 		if err != nil {
 			return nil, err
@@ -129,7 +130,7 @@ func (s *Service) domainWithHeadState(ctx context.Context, slot types.Slot, doma
 	if err != nil {
 		return nil, err
 	}
-	return helpers.Domain(headState.Fork(), core.SlotToEpoch(headState.Slot()), domain, headState.GenesisValidatorRoot())
+	return signing.Domain(headState.Fork(), slots.ToEpoch(headState.Slot()), domain, headState.GenesisValidatorsRoot())
 }

 // returns the head state that is advanced up to `slot`. It utilizes the cache `syncCommitteeHeadState` by retrieving using `slot` as key.
@@ -156,11 +157,9 @@ func (s *Service) getSyncCommitteeHeadState(ctx context.Context, slot types.Slot
 		if headState == nil || headState.IsNil() {
 			return nil, errors.New("nil state")
 		}
-		if slot > headState.Slot() {
-			headState, err = transition.ProcessSlots(ctx, headState, slot)
-			if err != nil {
-				return nil, err
-			}
+		headState, err = transition.ProcessSlotsIfPossible(ctx, headState, slot)
+		if err != nil {
+			return nil, err
 		}
 		syncHeadStateMiss.Inc()
 		err = syncCommitteeHeadStateCache.Put(slot, headState)
--- a/beacon-chain/blockchain/head_sync_committee_info_test.go
+++ b/beacon-chain/blockchain/head_sync_committee_info_test.go
@@ -6,19 +6,19 @@ import (

 	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/beacon-chain/cache"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/signing"
 	dbtest "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
+	"github.com/prysmaticlabs/prysm/time/slots"
 )

 func TestService_headSyncCommitteeFetcher_Errors(t *testing.T) {
 	beaconDB := dbtest.SetupDB(t)
 	c := &Service{
-		cfg: &Config{
+		cfg: &config{
 			StateGen: stategen.New(beaconDB),
 		},
 	}
@@ -36,7 +36,7 @@ func TestService_headSyncCommitteeFetcher_Errors(t *testing.T) {
 func TestService_HeadDomainFetcher_Errors(t *testing.T) {
 	beaconDB := dbtest.SetupDB(t)
 	c := &Service{
-		cfg: &Config{
+		cfg: &config{
 			StateGen: stategen.New(beaconDB),
 		},
 	}
@@ -52,7 +52,7 @@ func TestService_HeadDomainFetcher_Errors(t *testing.T) {
 }

 func TestService_HeadSyncCommitteeIndices(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

@@ -75,7 +75,7 @@ func TestService_HeadSyncCommitteeIndices(t *testing.T) {
 }

 func TestService_headCurrentSyncCommitteeIndices(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

@@ -89,7 +89,7 @@ func TestService_headCurrentSyncCommitteeIndices(t *testing.T) {
 }

 func TestService_headNextSyncCommitteeIndices(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

@@ -103,7 +103,7 @@ func TestService_headNextSyncCommitteeIndices(t *testing.T) {
 }

 func TestService_HeadSyncCommitteePubKeys(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

@@ -118,11 +118,11 @@ func TestService_HeadSyncCommitteePubKeys(t *testing.T) {
 }

 func TestService_HeadSyncCommitteeDomain(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

-	wanted, err := helpers.Domain(s.Fork(), core.SlotToEpoch(s.Slot()), params.BeaconConfig().DomainSyncCommittee, s.GenesisValidatorRoot())
+	wanted, err := signing.Domain(s.Fork(), slots.ToEpoch(s.Slot()), params.BeaconConfig().DomainSyncCommittee, s.GenesisValidatorsRoot())
 	require.NoError(t, err)

 	d, err := c.HeadSyncCommitteeDomain(context.Background(), 0)
@@ -132,11 +132,11 @@ func TestService_HeadSyncCommitteeDomain(t *testing.T) {
 }

 func TestService_HeadSyncContributionProofDomain(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

-	wanted, err := helpers.Domain(s.Fork(), core.SlotToEpoch(s.Slot()), params.BeaconConfig().DomainContributionAndProof, s.GenesisValidatorRoot())
+	wanted, err := signing.Domain(s.Fork(), slots.ToEpoch(s.Slot()), params.BeaconConfig().DomainContributionAndProof, s.GenesisValidatorsRoot())
 	require.NoError(t, err)

 	d, err := c.HeadSyncContributionProofDomain(context.Background(), 0)
@@ -146,11 +146,11 @@ func TestService_HeadSyncContributionProofDomain(t *testing.T) {
 }

 func TestService_HeadSyncSelectionProofDomain(t *testing.T) {
-	s, _ := testutil.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
+	s, _ := util.DeterministicGenesisStateAltair(t, params.BeaconConfig().TargetCommitteeSize)
 	c := &Service{}
 	c.head = &head{state: s}

-	wanted, err := helpers.Domain(s.Fork(), core.SlotToEpoch(s.Slot()), params.BeaconConfig().DomainSyncCommitteeSelectionProof, s.GenesisValidatorRoot())
+	wanted, err := signing.Domain(s.Fork(), slots.ToEpoch(s.Slot()), params.BeaconConfig().DomainSyncCommitteeSelectionProof, s.GenesisValidatorsRoot())
 	require.NoError(t, err)

 	d, err := c.HeadSyncSelectionProofDomain(context.Background(), 0)
@@ -164,7 +164,7 @@ func TestSyncCommitteeHeadStateCache_RoundTrip(t *testing.T) {
 	t.Cleanup(func() {
 		syncCommitteeHeadStateCache = cache.NewSyncCommitteeHeadState()
 	})
-	beaconState, _ := testutil.DeterministicGenesisStateAltair(t, 100)
+	beaconState, _ := util.DeterministicGenesisStateAltair(t, 100)
 	require.NoError(t, beaconState.SetSlot(100))
 	cachedState, err := c.Get(101)
 	require.ErrorContains(t, cache.ErrNotFound.Error(), err)
--- a/beacon-chain/blockchain/head_test.go
+++ b/beacon-chain/blockchain/head_test.go
@@ -8,16 +8,16 @@ import (

 	types "github.com/prysmaticlabs/eth2-types"
 	mock "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
 	"github.com/prysmaticlabs/prysm/config/features"
+	"github.com/prysmaticlabs/prysm/config/params"
 	ethpbv1 "github.com/prysmaticlabs/prysm/proto/eth/v1"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 )

@@ -38,9 +38,9 @@ func TestSaveHead_Different(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	service := setupBeaconChain(t, beaconDB)

-	testutil.NewBeaconBlock()
+	util.NewBeaconBlock()
 	oldBlock := wrapper.WrappedPhase0SignedBeaconBlock(
-		testutil.NewBeaconBlock(),
+		util.NewBeaconBlock(),
 	)
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(context.Background(), oldBlock))
 	oldRoot, err := oldBlock.Block().HashTreeRoot()
@@ -51,14 +51,14 @@ func TestSaveHead_Different(t *testing.T) {
 		block: oldBlock,
 	}

-	newHeadSignedBlock := testutil.NewBeaconBlock()
+	newHeadSignedBlock := util.NewBeaconBlock()
 	newHeadSignedBlock.Block.Slot = 1
 	newHeadBlock := newHeadSignedBlock.Block

 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(context.Background(), wrapper.WrappedPhase0SignedBeaconBlock(newHeadSignedBlock)))
 	newRoot, err := newHeadBlock.HashTreeRoot()
 	require.NoError(t, err)
-	headState, err := testutil.NewBeaconState()
+	headState, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, headState.SetSlot(1))
 	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(context.Background(), &ethpb.StateSummary{Slot: 1, Root: newRoot[:]}))
@@ -81,7 +81,7 @@ func TestSaveHead_Different_Reorg(t *testing.T) {
 	service := setupBeaconChain(t, beaconDB)

 	oldBlock := wrapper.WrappedPhase0SignedBeaconBlock(
-		testutil.NewBeaconBlock(),
+		util.NewBeaconBlock(),
 	)
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(context.Background(), oldBlock))
 	oldRoot, err := oldBlock.Block().HashTreeRoot()
@@ -93,7 +93,7 @@ func TestSaveHead_Different_Reorg(t *testing.T) {
 	}

 	reorgChainParent := [32]byte{'B'}
-	newHeadSignedBlock := testutil.NewBeaconBlock()
+	newHeadSignedBlock := util.NewBeaconBlock()
 	newHeadSignedBlock.Block.Slot = 1
 	newHeadSignedBlock.Block.ParentRoot = reorgChainParent[:]
 	newHeadBlock := newHeadSignedBlock.Block
@@ -101,7 +101,7 @@ func TestSaveHead_Different_Reorg(t *testing.T) {
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(context.Background(), wrapper.WrappedPhase0SignedBeaconBlock(newHeadSignedBlock)))
 	newRoot, err := newHeadBlock.HashTreeRoot()
 	require.NoError(t, err)
-	headState, err := testutil.NewBeaconState()
+	headState, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, headState.SetSlot(1))
 	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(context.Background(), &ethpb.StateSummary{Slot: 1, Root: newRoot[:]}))
@@ -123,40 +123,42 @@ func TestSaveHead_Different_Reorg(t *testing.T) {
 func TestCacheJustifiedStateBalances_CanCache(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	service := setupBeaconChain(t, beaconDB)
+	ctx := context.Background()

-	state, _ := testutil.DeterministicGenesisState(t, 100)
+	state, _ := util.DeterministicGenesisState(t, 100)
 	r := [32]byte{'a'}
 	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(context.Background(), &ethpb.StateSummary{Root: r[:]}))
 	require.NoError(t, service.cfg.BeaconDB.SaveState(context.Background(), state, r))
-	require.NoError(t, service.cacheJustifiedStateBalances(context.Background(), r))
-	require.DeepEqual(t, service.getJustifiedBalances(), state.Balances(), "Incorrect justified balances")
+	balances, err := service.justifiedBalances.get(ctx, r)
+	require.NoError(t, err)
+	require.DeepEqual(t, balances, state.Balances(), "Incorrect justified balances")
 }

 func TestUpdateHead_MissingJustifiedRoot(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	service := setupBeaconChain(t, beaconDB)

-	b := testutil.NewBeaconBlock()
+	b := util.NewBeaconBlock()
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(context.Background(), wrapper.WrappedPhase0SignedBeaconBlock(b)))
 	r, err := b.Block.HashTreeRoot()
 	require.NoError(t, err)

-	service.justifiedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.finalizedCheckpt = &ethpb.Checkpoint{}
-	service.bestJustifiedCheckpt = &ethpb.Checkpoint{}
+	service.store.SetJustifiedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{})
+	service.store.SetBestJustifiedCheckpt(&ethpb.Checkpoint{})

 	require.NoError(t, service.updateHead(context.Background(), []uint64{}))
 }

 func Test_notifyNewHeadEvent(t *testing.T) {
 	t.Run("genesis_state_root", func(t *testing.T) {
-		bState, _ := testutil.DeterministicGenesisState(t, 10)
+		bState, _ := util.DeterministicGenesisState(t, 10)
 		notifier := &mock.MockStateNotifier{RecordEvents: true}
 		srv := &Service{
-			cfg: &Config{
+			cfg: &config{
 				StateNotifier: notifier,
 			},
-			genesisRoot: [32]byte{1},
+			originBlockRoot: [32]byte{1},
 		}
 		newHeadStateRoot := [32]byte{2}
 		newHeadRoot := [32]byte{3}
@@ -172,24 +174,24 @@ func Test_notifyNewHeadEvent(t *testing.T) {
 			Block:                     newHeadRoot[:],
 			State:                     newHeadStateRoot[:],
 			EpochTransition:           false,
-			PreviousDutyDependentRoot: srv.genesisRoot[:],
-			CurrentDutyDependentRoot:  srv.genesisRoot[:],
+			PreviousDutyDependentRoot: srv.originBlockRoot[:],
+			CurrentDutyDependentRoot:  srv.originBlockRoot[:],
 		}
 		require.DeepSSZEqual(t, wanted, eventHead)
 	})
 	t.Run("non_genesis_values", func(t *testing.T) {
-		bState, _ := testutil.DeterministicGenesisState(t, 10)
+		bState, _ := util.DeterministicGenesisState(t, 10)
 		notifier := &mock.MockStateNotifier{RecordEvents: true}
 		genesisRoot := [32]byte{1}
 		srv := &Service{
-			cfg: &Config{
+			cfg: &config{
 				StateNotifier: notifier,
 			},
-			genesisRoot: genesisRoot,
+			originBlockRoot: genesisRoot,
 		}
-		epoch1Start, err := core.StartSlot(1)
+		epoch1Start, err := slots.EpochStart(1)
 		require.NoError(t, err)
-		epoch2Start, err := core.StartSlot(1)
+		epoch2Start, err := slots.EpochStart(1)
 		require.NoError(t, err)
 		require.NoError(t, bState.SetSlot(epoch1Start))

@@ -206,7 +208,7 @@ func Test_notifyNewHeadEvent(t *testing.T) {
 			Slot:                      epoch2Start,
 			Block:                     newHeadRoot[:],
 			State:                     newHeadStateRoot[:],
-			EpochTransition:           false,
+			EpochTransition:           true,
 			PreviousDutyDependentRoot: genesisRoot[:],
 			CurrentDutyDependentRoot:  make([]byte, 32),
 		}
@@ -220,8 +222,8 @@ func TestSaveOrphanedAtts(t *testing.T) {
 	})
 	defer resetCfg()

-	genesis, keys := testutil.DeterministicGenesisState(t, 64)
-	b, err := testutil.GenerateFullBlock(genesis, keys, testutil.DefaultBlockGenConfig(), 1)
+	genesis, keys := util.DeterministicGenesisState(t, 64)
+	b, err := util.GenerateFullBlock(genesis, keys, util.DefaultBlockGenConfig(), 1)
 	assert.NoError(t, err)
 	r, err := b.Block.HashTreeRoot()
 	require.NoError(t, err)
@@ -246,8 +248,8 @@ func TestSaveOrphanedAtts_CanFilter(t *testing.T) {
 	})
 	defer resetCfg()

-	genesis, keys := testutil.DeterministicGenesisState(t, 64)
-	b, err := testutil.GenerateFullBlock(genesis, keys, testutil.DefaultBlockGenConfig(), 1)
+	genesis, keys := util.DeterministicGenesisState(t, 64)
+	b, err := util.GenerateFullBlock(genesis, keys, util.DefaultBlockGenConfig(), 1)
 	assert.NoError(t, err)
 	r, err := b.Block.HashTreeRoot()
 	require.NoError(t, err)
--- a/beacon-chain/blockchain/info.go
+++ b/beacon-chain/blockchain/info.go
@@ -1,99 +0,0 @@
-package blockchain
-
-import (
-	"encoding/hex"
-	"fmt"
-	"net/http"
-
-	"github.com/emicklei/dot"
-	"github.com/prysmaticlabs/prysm/shared/params"
-)
-
-const template = `<html>
-<head>
-    <script src="//cdnjs.cloudflare.com/ajax/libs/viz.js/2.1.2/viz.js"></script>
-    <script src="//cdnjs.cloudflare.com/ajax/libs/viz.js/2.1.2/full.render.js"></script>
-<body>
-    <script type="application/javascript">
-        var graph = ` + "`%s`;" + `
-        var viz = new Viz();
-        viz.renderSVGElement(graph) // reading the graph.
-            .then(function(element) {
-                document.body.appendChild(element); // appends to document.
-            })
-            .catch(error => {
-                // Create a new Viz instance (@see Caveats page for more info)
-                viz = new Viz();
-                // Possibly display the error
-                console.error(error);
-            });
-    </script>
-</head>
-</body>
-</html>`
-
-// TreeHandler is a handler to serve /tree page in metrics.
-func (s *Service) TreeHandler(w http.ResponseWriter, r *http.Request) {
-	headState, err := s.HeadState(r.Context())
-	if err != nil {
-		log.WithError(err).Error("Could not get head state")
-		return
-	}
-	if headState == nil || headState.IsNil() {
-		if _, err := w.Write([]byte("Unavailable during initial syncing")); err != nil {
-			log.WithError(err).Error("Failed to render p2p info page")
-		}
-	}
-
-	nodes := s.cfg.ForkChoiceStore.Nodes()
-
-	graph := dot.NewGraph(dot.Directed)
-	graph.Attr("rankdir", "RL")
-	graph.Attr("labeljust", "l")
-
-	dotNodes := make([]*dot.Node, len(nodes))
-	avgBalance := uint64(averageBalance(headState.Balances()))
-
-	for i := len(nodes) - 1; i >= 0; i-- {
-		// Construct label for each node.
-		slot := fmt.Sprintf("%d", nodes[i].Slot())
-		weight := fmt.Sprintf("%d", nodes[i].Weight()/1e9) // Convert unit Gwei to unit ETH.
-		votes := fmt.Sprintf("%d", nodes[i].Weight()/1e9/avgBalance)
-		index := fmt.Sprintf("%d", i)
-		g := nodes[i].Graffiti()
-		graffiti := hex.EncodeToString(g[:8])
-		label := "slot: " + slot + "\n votes: " + votes + "\n weight: " + weight + "\n graffiti: " + graffiti
-		var dotN dot.Node
-		if nodes[i].Parent() != ^uint64(0) {
-			dotN = graph.Node(index).Box().Attr("label", label)
-		}
-
-		if nodes[i].Slot() == s.HeadSlot() &&
-			nodes[i].BestDescendant() == ^uint64(0) &&
-			nodes[i].Parent() != ^uint64(0) {
-			dotN = dotN.Attr("color", "green")
-		}
-
-		dotNodes[i] = &dotN
-	}
-
-	for i := len(nodes) - 1; i >= 0; i-- {
-		if nodes[i].Parent() != ^uint64(0) && nodes[i].Parent() < uint64(len(dotNodes)) {
-			graph.Edge(*dotNodes[i], *dotNodes[nodes[i].Parent()])
-		}
-	}
-
-	w.WriteHeader(http.StatusOK)
-	w.Header().Set("Content-Type", "text/html")
-	if _, err := fmt.Fprintf(w, template, graph.String()); err != nil {
-		log.WithError(err).Error("Failed to render p2p info page")
-	}
-}
-
-func averageBalance(balances []uint64) float64 {
-	total := uint64(0)
-	for i := 0; i < len(balances); i++ {
-		total += balances[i]
-	}
-	return float64(total) / float64(len(balances)) / float64(params.BeaconConfig().GweiPerEth)
-}
--- a/beacon-chain/blockchain/info_test.go
+++ b/beacon-chain/blockchain/info_test.go
@@ -1,49 +0,0 @@
-package blockchain
-
-import (
-	"context"
-	"net/http"
-	"net/http/httptest"
-	"testing"
-
-	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
-	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
-	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
-	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
-)
-
-func TestService_TreeHandler(t *testing.T) {
-	req, err := http.NewRequest("GET", "/tree", nil)
-	require.NoError(t, err)
-
-	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
-	headState, err := testutil.NewBeaconState()
-	require.NoError(t, err)
-	require.NoError(t, headState.SetBalances([]uint64{params.BeaconConfig().GweiPerEth}))
-	cfg := &Config{
-		BeaconDB: beaconDB,
-		ForkChoiceStore: protoarray.New(
-			0, // justifiedEpoch
-			0, // finalizedEpoch
-			[32]byte{'a'},
-		),
-		StateGen: stategen.New(beaconDB),
-	}
-	s, err := NewService(ctx, cfg)
-	require.NoError(t, err)
-	require.NoError(t, s.cfg.ForkChoiceStore.ProcessBlock(ctx, 0, [32]byte{'a'}, [32]byte{'g'}, [32]byte{'c'}, 0, 0))
-	require.NoError(t, s.cfg.ForkChoiceStore.ProcessBlock(ctx, 1, [32]byte{'b'}, [32]byte{'a'}, [32]byte{'c'}, 0, 0))
-	s.setHead([32]byte{'a'}, wrapper.WrappedPhase0SignedBeaconBlock(testutil.NewBeaconBlock()), headState)
-
-	rr := httptest.NewRecorder()
-	handler := http.HandlerFunc(s.TreeHandler)
-
-	handler.ServeHTTP(rr, req)
-
-	assert.Equal(t, http.StatusOK, rr.Code)
-}
--- a/beacon-chain/blockchain/init_test.go
+++ b/beacon-chain/blockchain/init_test.go
@@ -1,7 +1,7 @@
 package blockchain

 import (
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/config/params"
 )

 func init() {
--- a/beacon-chain/blockchain/log.go
+++ b/beacon-chain/blockchain/log.go
@@ -5,12 +5,12 @@ import (
 	"fmt"
 	"time"

-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
+	"github.com/prysmaticlabs/prysm/config/params"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
 	"github.com/prysmaticlabs/prysm/runtime/version"
-	"github.com/prysmaticlabs/prysm/shared/params"
 	prysmTime "github.com/prysmaticlabs/prysm/time"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	"github.com/sirupsen/logrus"
 )

@@ -44,7 +44,7 @@ func logStateTransitionData(b block.BeaconBlock) {
 }

 func logBlockSyncStatus(block block.BeaconBlock, blockRoot [32]byte, finalized *ethpb.Checkpoint, receivedTime time.Time, genesisTime uint64) error {
-	startTime, err := core.SlotToTime(genesisTime, block.Slot())
+	startTime, err := slots.ToTime(genesisTime, block.Slot())
 	if err != nil {
 		return err
 	}
@@ -52,9 +52,11 @@ func logBlockSyncStatus(block block.BeaconBlock, blockRoot [32]byte, finalized *
 		"slot":           block.Slot(),
 		"slotInEpoch":    block.Slot() % params.BeaconConfig().SlotsPerEpoch,
 		"block":          fmt.Sprintf("0x%s...", hex.EncodeToString(blockRoot[:])[:8]),
-		"epoch":          core.SlotToEpoch(block.Slot()),
+		"epoch":          slots.ToEpoch(block.Slot()),
 		"finalizedEpoch": finalized.Epoch,
 		"finalizedRoot":  fmt.Sprintf("0x%s...", hex.EncodeToString(finalized.Root)[:8]),
+		"parentRoot":     fmt.Sprintf("0x%s...", hex.EncodeToString(block.ParentRoot())[:8]),
+		"version":        version.String(block.Version()),
 	}).Info("Synced new block")
 	log.WithFields(logrus.Fields{
 		"slot":                      block.Slot,
--- a/beacon-chain/blockchain/log_test.go
+++ b/beacon-chain/blockchain/log_test.go
@@ -6,7 +6,7 @@ import (
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 )

--- a/beacon-chain/blockchain/metrics.go
+++ b/beacon-chain/blockchain/metrics.go
@@ -10,11 +10,11 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/altair"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/epoch/precompute"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
 	"github.com/prysmaticlabs/prysm/runtime/version"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
 )

 var (
@@ -130,6 +130,14 @@ var (
 		Name: "sync_head_state_hit",
 		Help: "The number of sync head state requests that are present in the cache.",
 	})
+	stateBalanceCacheHit = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "state_balance_cache_hit",
+		Help: "Count the number of state balance cache hits.",
+	})
+	stateBalanceCacheMiss = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "state_balance_cache_miss",
+		Help: "Count the number of state balance cache hits.",
+	})
 )

 // reportSlotMetrics reports slot related metrics.
@@ -245,8 +253,8 @@ func reportEpochMetrics(ctx context.Context, postState, headState state.BeaconSt
 		if err != nil {
 			return err
 		}
-	case version.Altair:
-		v, b, err = altair.InitializeEpochValidators(ctx, headState)
+	case version.Altair, version.Bellatrix:
+		v, b, err = altair.InitializePrecomputeValidators(ctx, headState)
 		if err != nil {
 			return err
 		}
--- a/beacon-chain/blockchain/metrics_test.go
+++ b/beacon-chain/blockchain/metrics_test.go
@@ -5,14 +5,14 @@ import (
 	"testing"

 	eth "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
 )

 func TestReportEpochMetrics_BadHeadState(t *testing.T) {
-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
-	h, err := testutil.NewBeaconState()
+	h, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, h.SetValidators(nil))
 	err = reportEpochMetrics(context.Background(), s, h)
@@ -20,9 +20,9 @@ func TestReportEpochMetrics_BadHeadState(t *testing.T) {
 }

 func TestReportEpochMetrics_BadAttestation(t *testing.T) {
-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
-	h, err := testutil.NewBeaconState()
+	h, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, h.AppendCurrentEpochAttestations(&eth.PendingAttestation{InclusionDelay: 0}))
 	err = reportEpochMetrics(context.Background(), s, h)
@@ -30,12 +30,12 @@ func TestReportEpochMetrics_BadAttestation(t *testing.T) {
 }

 func TestReportEpochMetrics_SlashedValidatorOutOfBound(t *testing.T) {
-	h, _ := testutil.DeterministicGenesisState(t, 1)
+	h, _ := util.DeterministicGenesisState(t, 1)
 	v, err := h.ValidatorAtIndex(0)
 	require.NoError(t, err)
 	v.Slashed = true
 	require.NoError(t, h.UpdateValidatorAtIndex(0, v))
-	require.NoError(t, h.AppendCurrentEpochAttestations(&eth.PendingAttestation{InclusionDelay: 1, Data: testutil.HydrateAttestationData(&eth.AttestationData{})}))
+	require.NoError(t, h.AppendCurrentEpochAttestations(&eth.PendingAttestation{InclusionDelay: 1, Data: util.HydrateAttestationData(&eth.AttestationData{})}))
 	err = reportEpochMetrics(context.Background(), h, h)
 	require.ErrorContains(t, "slot 0 out of bounds", err)
 }
--- a/beacon-chain/blockchain/mock_engine_test.go
+++ b/beacon-chain/blockchain/mock_engine_test.go
@@ -0,0 +1,49 @@
+package blockchain
+
+import (
+	"context"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/pkg/errors"
+	enginev1 "github.com/prysmaticlabs/prysm/proto/engine/v1"
+)
+
+type mockEngineService struct {
+	newPayloadError error
+	forkchoiceError error
+	blks            map[[32]byte]*enginev1.ExecutionBlock
+}
+
+func (m *mockEngineService) NewPayload(context.Context, *enginev1.ExecutionPayload) ([]byte, error) {
+	return nil, m.newPayloadError
+}
+
+func (m *mockEngineService) ForkchoiceUpdated(context.Context, *enginev1.ForkchoiceState, *enginev1.PayloadAttributes) (*enginev1.PayloadIDBytes, []byte, error) {
+	return nil, nil, m.forkchoiceError
+}
+
+func (*mockEngineService) GetPayloadV1(
+	_ context.Context, _ enginev1.PayloadIDBytes,
+) *enginev1.ExecutionPayload {
+	return nil
+}
+
+func (*mockEngineService) GetPayload(context.Context, [8]byte) (*enginev1.ExecutionPayload, error) {
+	return nil, nil
+}
+
+func (*mockEngineService) ExchangeTransitionConfiguration(context.Context, *enginev1.TransitionConfiguration) error {
+	return nil
+}
+
+func (*mockEngineService) LatestExecutionBlock(context.Context) (*enginev1.ExecutionBlock, error) {
+	return nil, nil
+}
+
+func (m *mockEngineService) ExecutionBlockByHash(_ context.Context, hash common.Hash) (*enginev1.ExecutionBlock, error) {
+	blk, ok := m.blks[common.BytesToHash(hash.Bytes())]
+	if !ok {
+		return nil, errors.New("block not found")
+	}
+	return blk, nil
+}
--- a/beacon-chain/blockchain/mock_test.go
+++ b/beacon-chain/blockchain/mock_test.go
@@ -0,0 +1,50 @@
+package blockchain
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+)
+
+func testServiceOptsWithDB(t *testing.T) []Option {
+	beaconDB := testDB.SetupDB(t)
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	return []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+}
+
+// warning: only use these opts when you are certain there are no db calls
+// in your code path. this is a lightweight way to satisfy the stategen/beacondb
+// initialization requirements w/o the overhead of db init.
+func testServiceOptsNoDB() []Option {
+	return []Option{
+		withStateBalanceCache(satisfactoryStateBalanceCache()),
+	}
+}
+
+type mockStateByRooter struct {
+	state state.BeaconState
+	err   error
+}
+
+var _ stateByRooter = &mockStateByRooter{}
+
+func (m mockStateByRooter) StateByRoot(_ context.Context, _ [32]byte) (state.BeaconState, error) {
+	return m.state, m.err
+}
+
+// returns an instance of the state balance cache that can be used
+// to satisfy the requirement for one in NewService, but which will
+// always return an error if used.
+func satisfactoryStateBalanceCache() *stateBalanceCache {
+	err := errors.New("satisfactoryStateBalanceCache doesn't perform real caching")
+	return &stateBalanceCache{stateGen: mockStateByRooter{err: err}}
+}
--- a/beacon-chain/blockchain/new_slot.go
+++ b/beacon-chain/blockchain/new_slot.go
@@ -0,0 +1,72 @@
+package blockchain
+
+import (
+	"bytes"
+	"context"
+
+	"github.com/pkg/errors"
+	types "github.com/prysmaticlabs/eth2-types"
+	"github.com/prysmaticlabs/prysm/time/slots"
+)
+
+// NewSlot mimics the implementation of `on_tick` in fork choice consensus spec.
+// It resets the proposer boost root in fork choice, and it updates store's justified checkpoint
+// if a better checkpoint on the store's finalized checkpoint chain.
+// This should only be called at the start of every slot interval.
+//
+// Spec pseudocode definition:
+//    # Reset store.proposer_boost_root if this is a new slot
+//    if current_slot > previous_slot:
+//        store.proposer_boost_root = Root()
+//
+//    # Not a new epoch, return
+//    if not (current_slot > previous_slot and compute_slots_since_epoch_start(current_slot) == 0):
+//        return
+//
+//    # Update store.justified_checkpoint if a better checkpoint on the store.finalized_checkpoint chain
+//    if store.best_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
+//        finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
+//        ancestor_at_finalized_slot = get_ancestor(store, store.best_justified_checkpoint.root, finalized_slot)
+//        if ancestor_at_finalized_slot == store.finalized_checkpoint.root:
+//            store.justified_checkpoint = store.best_justified_checkpoint
+func (s *Service) NewSlot(ctx context.Context, slot types.Slot) error {
+
+	// Reset proposer boost root in fork choice.
+	if err := s.cfg.ForkChoiceStore.ResetBoostedProposerRoot(ctx); err != nil {
+		return errors.Wrap(err, "could not reset boosted proposer root in fork choice")
+	}
+
+	// Return if it's not a new epoch.
+	if !slots.IsEpochStart(slot) {
+		return nil
+	}
+
+	// Update store.justified_checkpoint if a better checkpoint on the store.finalized_checkpoint chain
+	bj := s.store.BestJustifiedCheckpt()
+	if bj == nil {
+		return errNilBestJustifiedInStore
+	}
+	j := s.store.JustifiedCheckpt()
+	if j == nil {
+		return errNilJustifiedInStore
+	}
+	f := s.store.FinalizedCheckpt()
+	if f == nil {
+		return errNilFinalizedInStore
+	}
+	if bj.Epoch > j.Epoch {
+		finalizedSlot, err := slots.EpochStart(f.Epoch)
+		if err != nil {
+			return err
+		}
+		r, err := s.ancestor(ctx, bj.Root, finalizedSlot)
+		if err != nil {
+			return err
+		}
+		if bytes.Equal(r, f.Root) {
+			s.store.SetJustifiedCheckpt(bj)
+		}
+	}
+	return nil
+
+}
--- a/beacon-chain/blockchain/new_slot_test.go
+++ b/beacon-chain/blockchain/new_slot_test.go
@@ -0,0 +1,100 @@
+package blockchain
+
+import (
+	"context"
+	"testing"
+
+	types "github.com/prysmaticlabs/eth2-types"
+	"github.com/prysmaticlabs/prysm/beacon-chain/blockchain/store"
+	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func TestService_newSlot(t *testing.T) {
+	beaconDB := testDB.SetupDB(t)
+	fcs := protoarray.New(0, 0, [32]byte{})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	ctx := context.Background()
+
+	require.NoError(t, fcs.ProcessBlock(ctx, 0, [32]byte{}, [32]byte{}, 0, 0, false))        // genesis
+	require.NoError(t, fcs.ProcessBlock(ctx, 32, [32]byte{'a'}, [32]byte{}, 0, 0, false))    // finalized
+	require.NoError(t, fcs.ProcessBlock(ctx, 64, [32]byte{'b'}, [32]byte{'a'}, 0, 0, false)) // justified
+	require.NoError(t, fcs.ProcessBlock(ctx, 96, [32]byte{'c'}, [32]byte{'a'}, 0, 0, false)) // best justified
+	require.NoError(t, fcs.ProcessBlock(ctx, 97, [32]byte{'d'}, [32]byte{}, 0, 0, false))    // bad
+
+	type args struct {
+		slot          types.Slot
+		finalized     *ethpb.Checkpoint
+		justified     *ethpb.Checkpoint
+		bestJustified *ethpb.Checkpoint
+		shouldEqual   bool
+	}
+	tests := []struct {
+		name string
+		args args
+	}{
+		{
+			name: "Not epoch boundary. No change",
+			args: args{
+				slot:          params.BeaconConfig().SlotsPerEpoch + 1,
+				finalized:     &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'a'}, 32)},
+				justified:     &ethpb.Checkpoint{Epoch: 2, Root: bytesutil.PadTo([]byte{'b'}, 32)},
+				bestJustified: &ethpb.Checkpoint{Epoch: 3, Root: bytesutil.PadTo([]byte{'c'}, 32)},
+				shouldEqual:   false,
+			},
+		},
+		{
+			name: "Justified higher than best justified. No change",
+			args: args{
+				slot:          params.BeaconConfig().SlotsPerEpoch,
+				finalized:     &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'a'}, 32)},
+				justified:     &ethpb.Checkpoint{Epoch: 3, Root: bytesutil.PadTo([]byte{'b'}, 32)},
+				bestJustified: &ethpb.Checkpoint{Epoch: 2, Root: bytesutil.PadTo([]byte{'c'}, 32)},
+				shouldEqual:   false,
+			},
+		},
+		{
+			name: "Best justified not on the same chain as finalized. No change",
+			args: args{
+				slot:          params.BeaconConfig().SlotsPerEpoch,
+				finalized:     &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'a'}, 32)},
+				justified:     &ethpb.Checkpoint{Epoch: 2, Root: bytesutil.PadTo([]byte{'b'}, 32)},
+				bestJustified: &ethpb.Checkpoint{Epoch: 3, Root: bytesutil.PadTo([]byte{'d'}, 32)},
+				shouldEqual:   false,
+			},
+		},
+		{
+			name: "Best justified on the same chain as finalized. Yes change",
+			args: args{
+				slot:          params.BeaconConfig().SlotsPerEpoch,
+				finalized:     &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'a'}, 32)},
+				justified:     &ethpb.Checkpoint{Epoch: 2, Root: bytesutil.PadTo([]byte{'b'}, 32)},
+				bestJustified: &ethpb.Checkpoint{Epoch: 3, Root: bytesutil.PadTo([]byte{'c'}, 32)},
+				shouldEqual:   true,
+			},
+		},
+	}
+	for _, test := range tests {
+		service, err := NewService(ctx, opts...)
+		require.NoError(t, err)
+		store := store.New(test.args.justified, test.args.finalized)
+		store.SetBestJustifiedCheckpt(test.args.bestJustified)
+		service.store = store
+
+		require.NoError(t, service.NewSlot(ctx, test.args.slot))
+		if test.args.shouldEqual {
+			require.DeepSSZEqual(t, service.store.BestJustifiedCheckpt(), service.store.JustifiedCheckpt())
+		} else {
+			require.DeepNotSSZEqual(t, service.store.BestJustifiedCheckpt(), service.store.JustifiedCheckpt())
+		}
+	}
+}
--- a/beacon-chain/blockchain/optimistic_sync.go
+++ b/beacon-chain/blockchain/optimistic_sync.go
@@ -0,0 +1,160 @@
+package blockchain
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/pkg/errors"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/blocks"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	v1 "github.com/prysmaticlabs/prysm/beacon-chain/powchain/engine-api-client/v1"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	enginev1 "github.com/prysmaticlabs/prysm/proto/engine/v1"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
+	"github.com/prysmaticlabs/prysm/runtime/version"
+	"github.com/sirupsen/logrus"
+)
+
+// notifyForkchoiceUpdate signals execution engine the fork choice updates. Execution engine should:
+// 1. Re-organizes the execution payload chain and corresponding state to make head_block_hash the head.
+// 2. Applies finality to the execution state: it irreversibly persists the chain of all execution payloads and corresponding state, up to and including finalized_block_hash.
+func (s *Service) notifyForkchoiceUpdate(ctx context.Context, headBlk block.BeaconBlock, finalizedRoot [32]byte) (*enginev1.PayloadIDBytes, error) {
+	if headBlk == nil || headBlk.IsNil() || headBlk.Body().IsNil() {
+		return nil, errors.New("nil head block")
+	}
+	// Must not call fork choice updated until the transition conditions are met on the Pow network.
+	if isPreBellatrix(headBlk.Version()) {
+		return nil, nil
+	}
+	isExecutionBlk, err := blocks.ExecutionBlock(headBlk.Body())
+	if err != nil {
+		return nil, errors.Wrap(err, "could not determine if block is execution block")
+	}
+	if !isExecutionBlk {
+		return nil, nil
+	}
+	headPayload, err := headBlk.Body().ExecutionPayload()
+	if err != nil {
+		return nil, errors.Wrap(err, "could not get execution payload")
+	}
+	finalizedBlock, err := s.cfg.BeaconDB.Block(ctx, s.ensureRootNotZeros(finalizedRoot))
+	if err != nil {
+		return nil, errors.Wrap(err, "could not get finalized block")
+	}
+	var finalizedHash []byte
+	if isPreBellatrix(finalizedBlock.Block().Version()) {
+		finalizedHash = params.BeaconConfig().ZeroHash[:]
+	} else {
+		payload, err := finalizedBlock.Block().Body().ExecutionPayload()
+		if err != nil {
+			return nil, errors.Wrap(err, "could not get finalized block execution payload")
+		}
+		finalizedHash = payload.BlockHash
+	}
+
+	fcs := &enginev1.ForkchoiceState{
+		HeadBlockHash:      headPayload.BlockHash,
+		SafeBlockHash:      headPayload.BlockHash,
+		FinalizedBlockHash: finalizedHash,
+	}
+
+	// payload attribute is only required when requesting payload, here we are just updating fork choice, so it is nil.
+	payloadID, _, err := s.cfg.ExecutionEngineCaller.ForkchoiceUpdated(ctx, fcs, nil /*payload attribute*/)
+	if err != nil {
+		switch err {
+		case v1.ErrAcceptedSyncingPayloadStatus:
+			log.WithFields(logrus.Fields{
+				"headSlot":      headBlk.Slot(),
+				"headHash":      fmt.Sprintf("%#x", bytesutil.Trunc(headPayload.BlockHash)),
+				"finalizedHash": fmt.Sprintf("%#x", bytesutil.Trunc(finalizedHash)),
+			}).Info("Called fork choice updated with optimistic block")
+			return payloadID, nil
+		default:
+			return nil, errors.Wrap(err, "could not notify forkchoice update from execution engine")
+		}
+	}
+	return payloadID, nil
+}
+
+// notifyForkchoiceUpdate signals execution engine on a new payload
+func (s *Service) notifyNewPayload(ctx context.Context, preStateVersion int, header *ethpb.ExecutionPayloadHeader, postState state.BeaconState, blk block.SignedBeaconBlock) error {
+	if postState == nil {
+		return errors.New("pre and post states must not be nil")
+	}
+	// Execution payload is only supported in Bellatrix and beyond.
+	if isPreBellatrix(postState.Version()) {
+		return nil
+	}
+	if err := helpers.BeaconBlockIsNil(blk); err != nil {
+		return err
+	}
+	body := blk.Block().Body()
+	enabled, err := blocks.ExecutionEnabled(postState, blk.Block().Body())
+	if err != nil {
+		return errors.Wrap(err, "could not determine if execution is enabled")
+	}
+	if !enabled {
+		return nil
+	}
+	payload, err := body.ExecutionPayload()
+	if err != nil {
+		return errors.Wrap(err, "could not get execution payload")
+	}
+	_, err = s.cfg.ExecutionEngineCaller.NewPayload(ctx, payload)
+	if err != nil {
+		switch err {
+		case v1.ErrAcceptedSyncingPayloadStatus:
+			log.WithFields(logrus.Fields{
+				"slot":      postState.Slot(),
+				"blockHash": fmt.Sprintf("%#x", bytesutil.Trunc(payload.BlockHash)),
+			}).Info("Called new payload with optimistic block")
+			return nil
+		default:
+			return errors.Wrap(err, "could not validate execution payload from execution engine")
+		}
+	}
+
+	// During the transition event, the transition block should be verified for sanity.
+	if isPreBellatrix(preStateVersion) {
+		return nil
+	}
+	atTransition, err := blocks.IsMergeTransitionBlockUsingPayloadHeader(header, body)
+	if err != nil {
+		return errors.Wrap(err, "could not check if merge block is terminal")
+	}
+	if !atTransition {
+		return nil
+	}
+	return s.validateMergeBlock(ctx, blk)
+}
+
+// isPreBellatrix returns true if input version is before bellatrix fork.
+func isPreBellatrix(v int) bool {
+	return v == version.Phase0 || v == version.Altair
+}
+
+// optimisticCandidateBlock returns true if this block can be optimistically synced.
+//
+// Spec pseudocode definition:
+// def is_optimistic_candidate_block(opt_store: OptimisticStore, current_slot: Slot, block: BeaconBlock) -> bool:
+//     justified_root = opt_store.block_states[opt_store.head_block_root].current_justified_checkpoint.root
+//     justified_is_execution_block = is_execution_block(opt_store.blocks[justified_root])
+//     block_is_deep = block.slot + SAFE_SLOTS_TO_IMPORT_OPTIMISTICALLY <= current_slot
+//     return justified_is_execution_block or block_is_deep
+func (s *Service) optimisticCandidateBlock(ctx context.Context, blk block.BeaconBlock) (bool, error) {
+	if blk.Slot()+params.BeaconConfig().SafeSlotsToImportOptimistically <= s.CurrentSlot() {
+		return true, nil
+	}
+	j := s.store.JustifiedCheckpt()
+	if j == nil {
+		return false, errNilJustifiedInStore
+	}
+	jBlock, err := s.cfg.BeaconDB.Block(ctx, bytesutil.ToBytes32(j.Root))
+	if err != nil {
+		return false, err
+	}
+	return blocks.ExecutionBlock(jBlock.Block().Body())
+}
--- a/beacon-chain/blockchain/optimistic_sync_test.go
+++ b/beacon-chain/blockchain/optimistic_sync_test.go
@@ -0,0 +1,450 @@
+package blockchain
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
+	engine "github.com/prysmaticlabs/prysm/beacon-chain/powchain/engine-api-client/v1"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	v1 "github.com/prysmaticlabs/prysm/proto/engine/v1"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
+	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
+	"github.com/prysmaticlabs/prysm/runtime/version"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
+	"github.com/prysmaticlabs/prysm/time/slots"
+)
+
+func Test_NotifyForkchoiceUpdate(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+	altairBlk, err := wrapper.WrappedSignedBeaconBlock(util.NewBeaconBlockAltair())
+	require.NoError(t, err)
+	altairBlkRoot, err := altairBlk.Block().HashTreeRoot()
+	require.NoError(t, err)
+	bellatrixBlk, err := wrapper.WrappedSignedBeaconBlock(util.NewBeaconBlockBellatrix())
+	require.NoError(t, err)
+	bellatrixBlkRoot, err := bellatrixBlk.Block().HashTreeRoot()
+	require.NoError(t, err)
+	require.NoError(t, beaconDB.SaveBlock(ctx, altairBlk))
+	require.NoError(t, beaconDB.SaveBlock(ctx, bellatrixBlk))
+
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	tests := []struct {
+		name             string
+		blk              block.BeaconBlock
+		finalizedRoot    [32]byte
+		newForkchoiceErr error
+		errString        string
+	}{
+		{
+			name:      "nil block",
+			errString: "nil head block",
+		},
+		{
+			name: "phase0 block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlock{Body: &ethpb.BeaconBlockBody{}})
+				require.NoError(t, err)
+				return b
+			}(),
+		},
+		{
+			name: "altair block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlockAltair{Body: &ethpb.BeaconBlockBodyAltair{}})
+				require.NoError(t, err)
+				return b
+			}(),
+		},
+		{
+			name: "not execution block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlockBellatrix{
+					Body: &ethpb.BeaconBlockBodyBellatrix{
+						ExecutionPayload: &v1.ExecutionPayload{
+							ParentHash:    make([]byte, fieldparams.RootLength),
+							FeeRecipient:  make([]byte, fieldparams.FeeRecipientLength),
+							StateRoot:     make([]byte, fieldparams.RootLength),
+							ReceiptsRoot:  make([]byte, fieldparams.RootLength),
+							LogsBloom:     make([]byte, fieldparams.LogsBloomLength),
+							PrevRandao:    make([]byte, fieldparams.RootLength),
+							BaseFeePerGas: make([]byte, fieldparams.RootLength),
+							BlockHash:     make([]byte, fieldparams.RootLength),
+						},
+					},
+				})
+				require.NoError(t, err)
+				return b
+			}(),
+		},
+		{
+			name: "happy case: finalized root is altair block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlockBellatrix{
+					Body: &ethpb.BeaconBlockBodyBellatrix{
+						ExecutionPayload: &v1.ExecutionPayload{},
+					},
+				})
+				require.NoError(t, err)
+				return b
+			}(),
+			finalizedRoot: altairBlkRoot,
+		},
+		{
+			name: "happy case: finalized root is bellatrix block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlockBellatrix{
+					Body: &ethpb.BeaconBlockBodyBellatrix{
+						ExecutionPayload: &v1.ExecutionPayload{},
+					},
+				})
+				require.NoError(t, err)
+				return b
+			}(),
+			finalizedRoot: bellatrixBlkRoot,
+		},
+		{
+			name: "forkchoice updated with optimistic block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlockBellatrix{
+					Body: &ethpb.BeaconBlockBodyBellatrix{
+						ExecutionPayload: &v1.ExecutionPayload{},
+					},
+				})
+				require.NoError(t, err)
+				return b
+			}(),
+			newForkchoiceErr: engine.ErrAcceptedSyncingPayloadStatus,
+			finalizedRoot:    bellatrixBlkRoot,
+		},
+		{
+			name: "forkchoice updated with invalid block",
+			blk: func() block.BeaconBlock {
+				b, err := wrapper.WrappedBeaconBlock(&ethpb.BeaconBlockBellatrix{
+					Body: &ethpb.BeaconBlockBodyBellatrix{
+						ExecutionPayload: &v1.ExecutionPayload{},
+					},
+				})
+				require.NoError(t, err)
+				return b
+			}(),
+			newForkchoiceErr: engine.ErrInvalidPayloadStatus,
+			finalizedRoot:    bellatrixBlkRoot,
+			errString:        "could not notify forkchoice update from execution engine: payload status is INVALID",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			engine := &mockEngineService{forkchoiceError: tt.newForkchoiceErr}
+			service.cfg.ExecutionEngineCaller = engine
+			_, err := service.notifyForkchoiceUpdate(ctx, tt.blk, tt.finalizedRoot)
+			if tt.errString != "" {
+				require.ErrorContains(t, tt.errString, err)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
+
+func Test_NotifyNewPayload(t *testing.T) {
+	cfg := params.BeaconConfig()
+	cfg.TerminalTotalDifficulty = "2"
+	params.OverrideBeaconConfig(cfg)
+
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	phase0State, _ := util.DeterministicGenesisState(t, 1)
+	altairState, _ := util.DeterministicGenesisStateAltair(t, 1)
+	bellatrixState, _ := util.DeterministicGenesisStateBellatrix(t, 2)
+	blk := &ethpb.SignedBeaconBlockBellatrix{
+		Block: &ethpb.BeaconBlockBellatrix{
+			Body: &ethpb.BeaconBlockBodyBellatrix{
+				ExecutionPayload: &v1.ExecutionPayload{},
+			},
+		},
+	}
+	bellatrixBlk, err := wrapper.WrappedSignedBeaconBlock(blk)
+	require.NoError(t, err)
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	tests := []struct {
+		name          string
+		preState      state.BeaconState
+		postState     state.BeaconState
+		blk           block.SignedBeaconBlock
+		newPayloadErr error
+		errString     string
+	}{
+		{
+			name:      "phase 0 post state",
+			postState: phase0State,
+			preState:  phase0State,
+		},
+		{
+			name:      "altair post state",
+			postState: altairState,
+			preState:  altairState,
+		},
+		{
+			name:      "nil post state",
+			preState:  phase0State,
+			errString: "pre and post states must not be nil",
+		},
+		{
+			name:      "nil beacon block",
+			postState: bellatrixState,
+			preState:  bellatrixState,
+			errString: "signed beacon block can't be nil",
+		},
+		{
+			name:          "new payload with optimistic block",
+			postState:     bellatrixState,
+			preState:      bellatrixState,
+			blk:           bellatrixBlk,
+			newPayloadErr: engine.ErrAcceptedSyncingPayloadStatus,
+		},
+		{
+			name:          "new payload with invalid block",
+			postState:     bellatrixState,
+			preState:      bellatrixState,
+			blk:           bellatrixBlk,
+			newPayloadErr: engine.ErrInvalidPayloadStatus,
+			errString:     "could not validate execution payload from execution engine: payload status is INVALID",
+		},
+		{
+			name:      "altair pre state",
+			postState: bellatrixState,
+			preState:  altairState,
+			blk:       bellatrixBlk,
+		},
+		{
+			name:      "could not get merge block",
+			postState: bellatrixState,
+			preState:  bellatrixState,
+			blk:       bellatrixBlk,
+			errString: "could not get merge block parent hash and total difficulty",
+		},
+		{
+			name:      "not at merge transition",
+			postState: bellatrixState,
+			preState:  bellatrixState,
+			blk: func() block.SignedBeaconBlock {
+				blk := &ethpb.SignedBeaconBlockBellatrix{
+					Block: &ethpb.BeaconBlockBellatrix{
+						Body: &ethpb.BeaconBlockBodyBellatrix{
+							ExecutionPayload: &v1.ExecutionPayload{
+								ParentHash:    make([]byte, fieldparams.RootLength),
+								FeeRecipient:  make([]byte, fieldparams.FeeRecipientLength),
+								StateRoot:     make([]byte, fieldparams.RootLength),
+								ReceiptsRoot:  make([]byte, fieldparams.RootLength),
+								LogsBloom:     make([]byte, fieldparams.LogsBloomLength),
+								PrevRandao:    make([]byte, fieldparams.RootLength),
+								BaseFeePerGas: make([]byte, fieldparams.RootLength),
+								BlockHash:     make([]byte, fieldparams.RootLength),
+							},
+						},
+					},
+				}
+				b, err := wrapper.WrappedSignedBeaconBlock(blk)
+				require.NoError(t, err)
+				return b
+			}(),
+		},
+		{
+			name:      "could not get merge block",
+			postState: bellatrixState,
+			preState:  bellatrixState,
+			blk:       bellatrixBlk,
+			errString: "could not get merge block parent hash and total difficulty",
+		},
+		{
+			name:      "happy case",
+			postState: bellatrixState,
+			preState:  bellatrixState,
+			blk: func() block.SignedBeaconBlock {
+				blk := &ethpb.SignedBeaconBlockBellatrix{
+					Block: &ethpb.BeaconBlockBellatrix{
+						Body: &ethpb.BeaconBlockBodyBellatrix{
+							ExecutionPayload: &v1.ExecutionPayload{
+								ParentHash: bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength),
+							},
+						},
+					},
+				}
+				b, err := wrapper.WrappedSignedBeaconBlock(blk)
+				require.NoError(t, err)
+				return b
+			}(),
+		},
+	}
+	for _, tt := range tests {
+		engine := &mockEngineService{newPayloadError: tt.newPayloadErr, blks: map[[32]byte]*v1.ExecutionBlock{}}
+		engine.blks[[32]byte{'a'}] = &v1.ExecutionBlock{
+			ParentHash:      bytesutil.PadTo([]byte{'b'}, fieldparams.RootLength),
+			TotalDifficulty: "0x2",
+		}
+		engine.blks[[32]byte{'b'}] = &v1.ExecutionBlock{
+			ParentHash:      bytesutil.PadTo([]byte{'3'}, fieldparams.RootLength),
+			TotalDifficulty: "0x1",
+		}
+		service.cfg.ExecutionEngineCaller = engine
+		var payload *ethpb.ExecutionPayloadHeader
+		if tt.preState.Version() == version.Bellatrix {
+			payload, err = tt.preState.LatestExecutionPayloadHeader()
+			require.NoError(t, err)
+		}
+		err := service.notifyNewPayload(ctx, tt.preState.Version(), payload, tt.postState, tt.blk)
+		if tt.errString != "" {
+			require.ErrorContains(t, tt.errString, err)
+		} else {
+			require.NoError(t, err)
+		}
+	}
+}
+
+func Test_IsOptimisticCandidateBlock(t *testing.T) {
+	params.SetupTestConfigCleanup(t)
+	params.OverrideBeaconConfig(params.MainnetConfig())
+
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	params.BeaconConfig().SafeSlotsToImportOptimistically = 128
+	service.genesisTime = time.Now().Add(-time.Second * 12 * 2 * 128)
+
+	tests := []struct {
+		name      string
+		blk       block.BeaconBlock
+		justified block.SignedBeaconBlock
+		want      bool
+	}{
+		{
+			name: "deep block",
+			blk: func(tt *testing.T) block.BeaconBlock {
+				blk := util.NewBeaconBlockBellatrix()
+				blk.Block.Slot = 1
+				wr, err := wrapper.WrappedBellatrixBeaconBlock(blk.Block)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			justified: func(tt *testing.T) block.SignedBeaconBlock {
+				blk := util.NewBeaconBlockBellatrix()
+				blk.Block.Slot = 32
+				wr, err := wrapper.WrappedBellatrixSignedBeaconBlock(blk)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			want: true,
+		},
+		{
+			name: "shallow block, Altair justified chkpt",
+			blk: func(tt *testing.T) block.BeaconBlock {
+				blk := util.NewBeaconBlockAltair()
+				blk.Block.Slot = 200
+				wr, err := wrapper.WrappedAltairBeaconBlock(blk.Block)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			justified: func(tt *testing.T) block.SignedBeaconBlock {
+				blk := util.NewBeaconBlockAltair()
+				blk.Block.Slot = 32
+				wr, err := wrapper.WrappedAltairSignedBeaconBlock(blk)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			want: false,
+		},
+		{
+			name: "shallow block, Bellatrix justified chkpt without execution",
+			blk: func(tt *testing.T) block.BeaconBlock {
+				blk := util.NewBeaconBlockBellatrix()
+				blk.Block.Slot = 200
+				wr, err := wrapper.WrappedBellatrixBeaconBlock(blk.Block)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			justified: func(tt *testing.T) block.SignedBeaconBlock {
+				blk := util.NewBeaconBlockBellatrix()
+				blk.Block.Slot = 32
+				wr, err := wrapper.WrappedBellatrixSignedBeaconBlock(blk)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			want: false,
+		},
+		{
+			name: "shallow block, execution enabled justified chkpt",
+			blk: func(tt *testing.T) block.BeaconBlock {
+				blk := util.NewBeaconBlockBellatrix()
+				blk.Block.Slot = 200
+				wr, err := wrapper.WrappedBellatrixBeaconBlock(blk.Block)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			justified: func(tt *testing.T) block.SignedBeaconBlock {
+				blk := util.NewBeaconBlockBellatrix()
+				blk.Block.Slot = 32
+				blk.Block.Body.ExecutionPayload.ParentHash = bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength)
+				blk.Block.Body.ExecutionPayload.FeeRecipient = bytesutil.PadTo([]byte{'a'}, fieldparams.FeeRecipientLength)
+				blk.Block.Body.ExecutionPayload.StateRoot = bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength)
+				blk.Block.Body.ExecutionPayload.ReceiptsRoot = bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength)
+				blk.Block.Body.ExecutionPayload.LogsBloom = bytesutil.PadTo([]byte{'a'}, fieldparams.LogsBloomLength)
+				blk.Block.Body.ExecutionPayload.PrevRandao = bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength)
+				blk.Block.Body.ExecutionPayload.BaseFeePerGas = bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength)
+				blk.Block.Body.ExecutionPayload.BlockHash = bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength)
+				wr, err := wrapper.WrappedBellatrixSignedBeaconBlock(blk)
+				require.NoError(tt, err)
+				return wr
+			}(t),
+			want: true,
+		},
+	}
+	for _, tt := range tests {
+		jroot, err := tt.justified.Block().HashTreeRoot()
+		require.NoError(t, err)
+		require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, tt.justified))
+		service.store.SetJustifiedCheckpt(
+			&ethpb.Checkpoint{
+				Root:  jroot[:],
+				Epoch: slots.ToEpoch(tt.justified.Block().Slot()),
+			})
+		candidate, err := service.optimisticCandidateBlock(ctx, tt.blk)
+		require.NoError(t, err)
+		require.Equal(t, tt.want, candidate, tt.name)
+	}
+}
--- a/beacon-chain/blockchain/options.go
+++ b/beacon-chain/blockchain/options.go
@@ -0,0 +1,155 @@
+package blockchain
+
+import (
+	"github.com/prysmaticlabs/prysm/async/event"
+	"github.com/prysmaticlabs/prysm/beacon-chain/cache/depositcache"
+	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
+	"github.com/prysmaticlabs/prysm/beacon-chain/db"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice"
+	"github.com/prysmaticlabs/prysm/beacon-chain/operations/attestations"
+	"github.com/prysmaticlabs/prysm/beacon-chain/operations/slashings"
+	"github.com/prysmaticlabs/prysm/beacon-chain/operations/voluntaryexits"
+	"github.com/prysmaticlabs/prysm/beacon-chain/p2p"
+	"github.com/prysmaticlabs/prysm/beacon-chain/powchain"
+	enginev1 "github.com/prysmaticlabs/prysm/beacon-chain/powchain/engine-api-client/v1"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+)
+
+type Option func(s *Service) error
+
+// WithMaxGoroutines to control resource use of the blockchain service.
+func WithMaxGoroutines(x int) Option {
+	return func(s *Service) error {
+		s.cfg.MaxRoutines = x
+		return nil
+	}
+}
+
+// WithWeakSubjectivityCheckpoint for checkpoint sync.
+func WithWeakSubjectivityCheckpoint(c *ethpb.Checkpoint) Option {
+	return func(s *Service) error {
+		s.cfg.WeakSubjectivityCheckpt = c
+		return nil
+	}
+}
+
+// WithDatabase for head access.
+func WithDatabase(beaconDB db.HeadAccessDatabase) Option {
+	return func(s *Service) error {
+		s.cfg.BeaconDB = beaconDB
+		return nil
+	}
+}
+
+// WithChainStartFetcher to retrieve information about genesis.
+func WithChainStartFetcher(f powchain.ChainStartFetcher) Option {
+	return func(s *Service) error {
+		s.cfg.ChainStartFetcher = f
+		return nil
+	}
+}
+
+// WithExecutionEngineCaller to call execution engine.
+func WithExecutionEngineCaller(c enginev1.Caller) Option {
+	return func(s *Service) error {
+		s.cfg.ExecutionEngineCaller = c
+		return nil
+	}
+}
+
+// WithDepositCache for deposit lifecycle after chain inclusion.
+func WithDepositCache(c *depositcache.DepositCache) Option {
+	return func(s *Service) error {
+		s.cfg.DepositCache = c
+		return nil
+	}
+}
+
+// WithAttestationPool for attestation lifecycle after chain inclusion.
+func WithAttestationPool(p attestations.Pool) Option {
+	return func(s *Service) error {
+		s.cfg.AttPool = p
+		return nil
+	}
+}
+
+// WithExitPool for exits lifecycle after chain inclusion.
+func WithExitPool(p voluntaryexits.PoolManager) Option {
+	return func(s *Service) error {
+		s.cfg.ExitPool = p
+		return nil
+	}
+}
+
+// WithSlashingPool for slashings lifecycle after chain inclusion.
+func WithSlashingPool(p slashings.PoolManager) Option {
+	return func(s *Service) error {
+		s.cfg.SlashingPool = p
+		return nil
+	}
+}
+
+// WithP2PBroadcaster to broadcast messages after appropriate processing.
+func WithP2PBroadcaster(p p2p.Broadcaster) Option {
+	return func(s *Service) error {
+		s.cfg.P2p = p
+		return nil
+	}
+}
+
+// WithStateNotifier to notify an event feed of state processing.
+func WithStateNotifier(n statefeed.Notifier) Option {
+	return func(s *Service) error {
+		s.cfg.StateNotifier = n
+		return nil
+	}
+}
+
+// WithForkChoiceStore to update an optimized fork-choice representation.
+func WithForkChoiceStore(f forkchoice.ForkChoicer) Option {
+	return func(s *Service) error {
+		s.cfg.ForkChoiceStore = f
+		return nil
+	}
+}
+
+// WithAttestationService for dealing with attestation lifecycles.
+func WithAttestationService(srv *attestations.Service) Option {
+	return func(s *Service) error {
+		s.cfg.AttService = srv
+		return nil
+	}
+}
+
+// WithStateGen for managing state regeneration and replay.
+func WithStateGen(g *stategen.State) Option {
+	return func(s *Service) error {
+		s.cfg.StateGen = g
+		return nil
+	}
+}
+
+// WithSlasherAttestationsFeed to forward attestations into slasher if enabled.
+func WithSlasherAttestationsFeed(f *event.Feed) Option {
+	return func(s *Service) error {
+		s.cfg.SlasherAttestationsFeed = f
+		return nil
+	}
+}
+
+func withStateBalanceCache(c *stateBalanceCache) Option {
+	return func(s *Service) error {
+		s.justifiedBalances = c
+		return nil
+	}
+}
+
+// WithFinalizedStateAtStartUp to store finalized state at start up.
+func WithFinalizedStateAtStartUp(st state.BeaconState) Option {
+	return func(s *Service) error {
+		s.cfg.FinalizedStateAtStartUp = st
+		return nil
+	}
+}
--- a/beacon-chain/blockchain/pow_block.go
+++ b/beacon-chain/blockchain/pow_block.go
@@ -0,0 +1,141 @@
+package blockchain
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
+	"github.com/holiman/uint256"
+	"github.com/pkg/errors"
+	types "github.com/prysmaticlabs/eth2-types"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	enginev1 "github.com/prysmaticlabs/prysm/proto/engine/v1"
+	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
+	"github.com/prysmaticlabs/prysm/time/slots"
+	"github.com/sirupsen/logrus"
+)
+
+// validateMergeBlock validates terminal block hash in the event of manual overrides before checking for total difficulty.
+//
+// def validate_merge_block(block: BeaconBlock) -> None:
+//    if TERMINAL_BLOCK_HASH != Hash32():
+//        # If `TERMINAL_BLOCK_HASH` is used as an override, the activation epoch must be reached.
+//        assert compute_epoch_at_slot(block.slot) >= TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH
+//        assert block.body.execution_payload.parent_hash == TERMINAL_BLOCK_HASH
+//        return
+//
+//    pow_block = get_pow_block(block.body.execution_payload.parent_hash)
+//    # Check if `pow_block` is available
+//    assert pow_block is not None
+//    pow_parent = get_pow_block(pow_block.parent_hash)
+//    # Check if `pow_parent` is available
+//    assert pow_parent is not None
+//    # Check if `pow_block` is a valid terminal PoW block
+//    assert is_valid_terminal_pow_block(pow_block, pow_parent)
+func (s *Service) validateMergeBlock(ctx context.Context, b block.SignedBeaconBlock) error {
+	if err := helpers.BeaconBlockIsNil(b); err != nil {
+		return err
+	}
+	payload, err := b.Block().Body().ExecutionPayload()
+	if err != nil {
+		return err
+	}
+	if payload == nil {
+		return errors.New("nil execution payload")
+	}
+	if err := validateTerminalBlockHash(b.Block().Slot(), payload); err != nil {
+		return errors.Wrap(err, "could not validate terminal block hash")
+	}
+	mergeBlockParentHash, mergeBlockTD, err := s.getBlkParentHashAndTD(ctx, payload.ParentHash)
+	if err != nil {
+		return errors.Wrap(err, "could not get merge block parent hash and total difficulty")
+	}
+	_, mergeBlockParentTD, err := s.getBlkParentHashAndTD(ctx, mergeBlockParentHash)
+	if err != nil {
+		return errors.Wrap(err, "could not get merge parent block total difficulty")
+	}
+	valid, err := validateTerminalBlockDifficulties(mergeBlockTD, mergeBlockParentTD)
+	if err != nil {
+		return err
+	}
+	if !valid {
+		return fmt.Errorf("invalid TTD, configTTD: %s, currentTTD: %s, parentTTD: %s",
+			params.BeaconConfig().TerminalTotalDifficulty, mergeBlockTD, mergeBlockParentTD)
+	}
+
+	log.WithFields(logrus.Fields{
+		"slot":                            b.Block().Slot(),
+		"mergeBlockHash":                  common.BytesToHash(payload.ParentHash).String(),
+		"mergeBlockParentHash":            common.BytesToHash(mergeBlockParentHash).String(),
+		"terminalTotalDifficulty":         params.BeaconConfig().TerminalTotalDifficulty,
+		"mergeBlockTotalDifficulty":       mergeBlockTD,
+		"mergeBlockParentTotalDifficulty": mergeBlockParentTD,
+	}).Info("Validated terminal block")
+
+	return nil
+}
+
+// getBlkParentHashAndTD retrieves the parent hash and total difficulty of the given block.
+func (s *Service) getBlkParentHashAndTD(ctx context.Context, blkHash []byte) ([]byte, *uint256.Int, error) {
+	blk, err := s.cfg.ExecutionEngineCaller.ExecutionBlockByHash(ctx, common.BytesToHash(blkHash))
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "could not get pow block")
+	}
+	if blk == nil {
+		return nil, nil, errors.New("pow block is nil")
+	}
+	blkTDBig, err := hexutil.DecodeBig(blk.TotalDifficulty)
+	if err != nil {
+		return nil, nil, errors.Wrap(err, "could not decode merge block total difficulty")
+	}
+	blkTDUint256, overflows := uint256.FromBig(blkTDBig)
+	if overflows {
+		return nil, nil, errors.New("total difficulty overflows")
+	}
+	return blk.ParentHash, blkTDUint256, nil
+}
+
+// validateTerminalBlockHash validates if the merge block is a valid terminal PoW block.
+// spec code:
+// if TERMINAL_BLOCK_HASH != Hash32():
+//        # If `TERMINAL_BLOCK_HASH` is used as an override, the activation epoch must be reached.
+//        assert compute_epoch_at_slot(block.slot) >= TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH
+//        assert block.body.execution_payload.parent_hash == TERMINAL_BLOCK_HASH
+//        return
+func validateTerminalBlockHash(blkSlot types.Slot, payload *enginev1.ExecutionPayload) error {
+	if bytesutil.ToBytes32(params.BeaconConfig().TerminalBlockHash.Bytes()) == [32]byte{} {
+		return nil
+	}
+	if params.BeaconConfig().TerminalBlockHashActivationEpoch > slots.ToEpoch(blkSlot) {
+		return errors.New("terminal block hash activation epoch not reached")
+	}
+	if !bytes.Equal(payload.ParentHash, params.BeaconConfig().TerminalBlockHash.Bytes()) {
+		return errors.New("parent hash does not match terminal block hash")
+	}
+	return nil
+}
+
+// validateTerminalBlockDifficulties validates terminal pow block by comparing own total difficulty with parent's total difficulty.
+//
+// def is_valid_terminal_pow_block(block: PowBlock, parent: PowBlock) -> bool:
+//    is_total_difficulty_reached = block.total_difficulty >= TERMINAL_TOTAL_DIFFICULTY
+//    is_parent_total_difficulty_valid = parent.total_difficulty < TERMINAL_TOTAL_DIFFICULTY
+//    return is_total_difficulty_reached and is_parent_total_difficulty_valid
+func validateTerminalBlockDifficulties(currentDifficulty *uint256.Int, parentDifficulty *uint256.Int) (bool, error) {
+	b, ok := new(big.Int).SetString(params.BeaconConfig().TerminalTotalDifficulty, 10)
+	if !ok {
+		return false, errors.New("failed to parse terminal total difficulty")
+	}
+	ttd, of := uint256.FromBig(b)
+	if of {
+		return false, errors.New("overflow terminal total difficulty")
+	}
+	totalDifficultyReached := currentDifficulty.Cmp(ttd) >= 0
+	parentTotalDifficultyValid := ttd.Cmp(parentDifficulty) > 0
+	return totalDifficultyReached && parentTotalDifficultyValid, nil
+}
--- a/beacon-chain/blockchain/pow_block_test.go
+++ b/beacon-chain/blockchain/pow_block_test.go
@@ -0,0 +1,210 @@
+package blockchain
+
+import (
+	"context"
+	"fmt"
+	"math/big"
+	"testing"
+
+	"github.com/holiman/uint256"
+	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	enginev1 "github.com/prysmaticlabs/prysm/proto/engine/v1"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func Test_validTerminalPowBlock(t *testing.T) {
+	tests := []struct {
+		name              string
+		currentDifficulty *uint256.Int
+		parentDifficulty  *uint256.Int
+		ttd               uint64
+		want              bool
+	}{
+		{
+			name:              "current > ttd, parent > ttd",
+			currentDifficulty: uint256.NewInt(2),
+			parentDifficulty:  uint256.NewInt(2),
+			ttd:               1,
+			want:              false,
+		},
+		{
+			name:              "current < ttd, parent < ttd",
+			currentDifficulty: uint256.NewInt(2),
+			parentDifficulty:  uint256.NewInt(2),
+			ttd:               3,
+			want:              false,
+		},
+		{
+			name:              "current == ttd, parent == ttd",
+			currentDifficulty: uint256.NewInt(2),
+			parentDifficulty:  uint256.NewInt(2),
+			ttd:               2,
+			want:              false,
+		},
+		{
+			name:              "current > ttd, parent == ttd",
+			currentDifficulty: uint256.NewInt(2),
+			parentDifficulty:  uint256.NewInt(1),
+			ttd:               1,
+			want:              false,
+		},
+		{
+			name:              "current == ttd, parent < ttd",
+			currentDifficulty: uint256.NewInt(2),
+			parentDifficulty:  uint256.NewInt(1),
+			ttd:               2,
+			want:              true,
+		},
+		{
+			name:              "current > ttd, parent < ttd",
+			currentDifficulty: uint256.NewInt(3),
+			parentDifficulty:  uint256.NewInt(1),
+			ttd:               2,
+			want:              true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			cfg := params.BeaconConfig()
+			cfg.TerminalTotalDifficulty = fmt.Sprint(tt.ttd)
+			params.OverrideBeaconConfig(cfg)
+			got, err := validateTerminalBlockDifficulties(tt.currentDifficulty, tt.parentDifficulty)
+			require.NoError(t, err)
+			if got != tt.want {
+				t.Errorf("validateTerminalBlockDifficulties() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func Test_validTerminalPowBlockSpecConfig(t *testing.T) {
+	cfg := params.BeaconConfig()
+	cfg.TerminalTotalDifficulty = "115792089237316195423570985008687907853269984665640564039457584007913129638912"
+	params.OverrideBeaconConfig(cfg)
+
+	i, _ := new(big.Int).SetString("115792089237316195423570985008687907853269984665640564039457584007913129638912", 10)
+	current, of := uint256.FromBig(i)
+	require.Equal(t, of, false)
+	i, _ = new(big.Int).SetString("115792089237316195423570985008687907853269984665640564039457584007913129638911", 10)
+	parent, of := uint256.FromBig(i)
+	require.Equal(t, of, false)
+
+	got, err := validateTerminalBlockDifficulties(current, parent)
+	require.NoError(t, err)
+	require.Equal(t, true, got)
+}
+
+func Test_validateMergeBlock(t *testing.T) {
+	cfg := params.BeaconConfig()
+	cfg.TerminalTotalDifficulty = "2"
+	params.OverrideBeaconConfig(cfg)
+
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	engine := &mockEngineService{blks: map[[32]byte]*enginev1.ExecutionBlock{}}
+	service.cfg.ExecutionEngineCaller = engine
+	engine.blks[[32]byte{'a'}] = &enginev1.ExecutionBlock{
+		ParentHash:      bytesutil.PadTo([]byte{'b'}, fieldparams.RootLength),
+		TotalDifficulty: "0x2",
+	}
+	engine.blks[[32]byte{'b'}] = &enginev1.ExecutionBlock{
+		ParentHash:      bytesutil.PadTo([]byte{'3'}, fieldparams.RootLength),
+		TotalDifficulty: "0x1",
+	}
+	blk := &ethpb.SignedBeaconBlockBellatrix{
+		Block: &ethpb.BeaconBlockBellatrix{
+			Slot: 1,
+			Body: &ethpb.BeaconBlockBodyBellatrix{
+				ExecutionPayload: &enginev1.ExecutionPayload{
+					ParentHash: bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength),
+				},
+			},
+		},
+	}
+	b, err := wrapper.WrappedSignedBeaconBlock(blk)
+	require.NoError(t, err)
+	require.NoError(t, service.validateMergeBlock(ctx, b))
+
+	cfg.TerminalTotalDifficulty = "1"
+	params.OverrideBeaconConfig(cfg)
+	require.ErrorContains(t, "invalid TTD, configTTD: 1, currentTTD: 2, parentTTD: 1", service.validateMergeBlock(ctx, b))
+}
+
+func Test_getBlkParentHashAndTD(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	engine := &mockEngineService{blks: map[[32]byte]*enginev1.ExecutionBlock{}}
+	service.cfg.ExecutionEngineCaller = engine
+	h := [32]byte{'a'}
+	p := [32]byte{'b'}
+	td := "0x1"
+	engine.blks[h] = &enginev1.ExecutionBlock{
+		ParentHash:      p[:],
+		TotalDifficulty: td,
+	}
+	parentHash, totalDifficulty, err := service.getBlkParentHashAndTD(ctx, h[:])
+	require.NoError(t, err)
+	require.Equal(t, p, bytesutil.ToBytes32(parentHash))
+	require.Equal(t, td, totalDifficulty.String())
+
+	_, _, err = service.getBlkParentHashAndTD(ctx, []byte{'c'})
+	require.ErrorContains(t, "could not get pow block: block not found", err)
+
+	engine.blks[h] = nil
+	_, _, err = service.getBlkParentHashAndTD(ctx, h[:])
+	require.ErrorContains(t, "pow block is nil", err)
+
+	engine.blks[h] = &enginev1.ExecutionBlock{
+		ParentHash:      p[:],
+		TotalDifficulty: "1",
+	}
+	_, _, err = service.getBlkParentHashAndTD(ctx, h[:])
+	require.ErrorContains(t, "could not decode merge block total difficulty: hex string without 0x prefix", err)
+
+	engine.blks[h] = &enginev1.ExecutionBlock{
+		ParentHash:      p[:],
+		TotalDifficulty: "0XFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF",
+	}
+	_, _, err = service.getBlkParentHashAndTD(ctx, h[:])
+	require.ErrorContains(t, "could not decode merge block total difficulty: hex number > 256 bits", err)
+}
+
+func Test_validateTerminalBlockHash(t *testing.T) {
+	require.NoError(t, validateTerminalBlockHash(1, &enginev1.ExecutionPayload{}))
+
+	cfg := params.BeaconConfig()
+	cfg.TerminalBlockHash = [32]byte{0x01}
+	params.OverrideBeaconConfig(cfg)
+	require.ErrorContains(t, "terminal block hash activation epoch not reached", validateTerminalBlockHash(1, &enginev1.ExecutionPayload{}))
+
+	cfg.TerminalBlockHashActivationEpoch = 0
+	params.OverrideBeaconConfig(cfg)
+	require.ErrorContains(t, "parent hash does not match terminal block hash", validateTerminalBlockHash(1, &enginev1.ExecutionPayload{}))
+
+	require.NoError(t, validateTerminalBlockHash(1, &enginev1.ExecutionPayload{ParentHash: cfg.TerminalBlockHash.Bytes()}))
+}
--- a/beacon-chain/blockchain/process_attestation.go
+++ b/beacon-chain/blockchain/process_attestation.go
@@ -2,19 +2,19 @@ package blockchain

 import (
 	"context"
+	"time"

 	"github.com/pkg/errors"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/attestation"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/time"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	"go.opencensus.io/trace"
 )

-// onAttestation is called whenever an attestation is received, verifies the attestation is valid and saves
+// OnAttestation is called whenever an attestation is received, verifies the attestation is valid and saves
 // it to the DB. As a stateless function, this does not hold nor delay attestation based on the spec descriptions.
 // The delay is handled by the caller in `processAttestations`.
 //
@@ -36,7 +36,7 @@ import (
 //
 //    # Update latest messages for attesting indices
 //    update_latest_messages(store, indexed_attestation.attesting_indices, attestation)
-func (s *Service) onAttestation(ctx context.Context, a *ethpb.Attestation) error {
+func (s *Service) OnAttestation(ctx context.Context, a *ethpb.Attestation) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.onAttestation")
 	defer span.End()

@@ -59,10 +59,10 @@ func (s *Service) onAttestation(ctx context.Context, a *ethpb.Attestation) error
 		return err
 	}

-	genesisTime := baseState.GenesisTime()
+	genesisTime := uint64(s.genesisTime.Unix())

 	// Verify attestation target is from current epoch or previous epoch.
-	if err := s.verifyAttTargetEpoch(ctx, genesisTime, uint64(time.Now().Unix()), tgt); err != nil {
+	if err := verifyAttTargetEpoch(ctx, genesisTime, uint64(time.Now().Unix()), tgt); err != nil {
 		return err
 	}

@@ -75,12 +75,12 @@ func (s *Service) onAttestation(ctx context.Context, a *ethpb.Attestation) error
 	// validate_aggregate_proof.go and validate_beacon_attestation.go

 	// Verify attestations can only affect the fork choice of subsequent slots.
-	if err := core.VerifySlotTime(genesisTime, a.Data.Slot+1, params.BeaconNetworkConfig().MaximumGossipClockDisparity); err != nil {
+	if err := slots.VerifyTime(genesisTime, a.Data.Slot+1, params.BeaconNetworkConfig().MaximumGossipClockDisparity); err != nil {
 		return err
 	}

 	// Use the target state to verify attesting indices are valid.
-	committee, err := helpers.BeaconCommitteeFromState(baseState, a.Data.Slot, a.Data.CommitteeIndex)
+	committee, err := helpers.BeaconCommitteeFromState(ctx, baseState, a.Data.Slot, a.Data.CommitteeIndex)
 	if err != nil {
 		return err
 	}
--- a/beacon-chain/blockchain/process_attestation_helpers.go
+++ b/beacon-chain/blockchain/process_attestation_helpers.go
@@ -8,13 +8,13 @@ import (
 	"github.com/pkg/errors"
 	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/async"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/time/slots"
 )

 // getAttPreState retrieves the att pre state by either from the cache or the DB.
@@ -38,15 +38,13 @@ func (s *Service) getAttPreState(ctx context.Context, c *ethpb.Checkpoint) (stat
 		return nil, errors.Wrapf(err, "could not get pre state for epoch %d", c.Epoch)
 	}

-	epochStartSlot, err := core.StartSlot(c.Epoch)
+	epochStartSlot, err := slots.EpochStart(c.Epoch)
 	if err != nil {
 		return nil, err
 	}
-	if epochStartSlot > baseState.Slot() {
-		baseState, err = transition.ProcessSlots(ctx, baseState, epochStartSlot)
-		if err != nil {
-			return nil, errors.Wrapf(err, "could not process slots up to epoch %d", c.Epoch)
-		}
+	baseState, err = transition.ProcessSlotsIfPossible(ctx, baseState, epochStartSlot)
+	if err != nil {
+		return nil, errors.Wrapf(err, "could not process slots up to epoch %d", c.Epoch)
 	}

 	// Sharing the same state across caches is perfectly fine here, the fetching
@@ -61,9 +59,9 @@ func (s *Service) getAttPreState(ctx context.Context, c *ethpb.Checkpoint) (stat
 }

 // verifyAttTargetEpoch validates attestation is from the current or previous epoch.
-func (s *Service) verifyAttTargetEpoch(_ context.Context, genesisTime, nowTime uint64, c *ethpb.Checkpoint) error {
+func verifyAttTargetEpoch(_ context.Context, genesisTime, nowTime uint64, c *ethpb.Checkpoint) error {
 	currentSlot := types.Slot((nowTime - genesisTime) / params.BeaconConfig().SecondsPerSlot)
-	currentEpoch := core.SlotToEpoch(currentSlot)
+	currentEpoch := slots.ToEpoch(currentSlot)
 	var prevEpoch types.Epoch
 	// Prevents previous epoch under flow
 	if currentEpoch > 1 {
@@ -87,7 +85,7 @@ func (s *Service) verifyBeaconBlock(ctx context.Context, data *ethpb.Attestation
 	if (b == nil || b.IsNil()) && s.hasInitSyncBlock(r) {
 		b = s.getInitSyncBlock(r)
 	}
-	if err := helpers.VerifyNilBeaconBlock(b); err != nil {
+	if err := helpers.BeaconBlockIsNil(b); err != nil {
 		return err
 	}
 	if b.Block().Slot() > data.Slot {
--- a/beacon-chain/blockchain/process_attestation_test.go
+++ b/beacon-chain/blockchain/process_attestation_test.go
@@ -3,62 +3,64 @@ package blockchain
 import (
 	"context"
 	"testing"
+	"time"

 	types "github.com/prysmaticlabs/eth2-types"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	doublylinkedtree "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/doubly-linked-tree"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
-	"github.com/prysmaticlabs/prysm/time"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
+	"github.com/prysmaticlabs/prysm/time/slots"
 )

-func TestStore_OnAttestation_ErrorConditions(t *testing.T) {
+func TestStore_OnAttestation_ErrorConditions_ProtoArray(t *testing.T) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{
-		BeaconDB:        beaconDB,
-		ForkChoiceStore: protoarray.New(0, 0, [32]byte{}),
-		StateGen:        stategen.New(beaconDB),
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithForkChoiceStore(protoarray.New(0, 0, [32]byte{})),
+		WithStateGen(stategen.New(beaconDB)),
 	}
-	service, err := NewService(ctx, cfg)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

 	_, err = blockTree1(t, beaconDB, []byte{'g'})
 	require.NoError(t, err)

-	BlkWithOutState := testutil.NewBeaconBlock()
+	BlkWithOutState := util.NewBeaconBlock()
 	BlkWithOutState.Block.Slot = 0
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(BlkWithOutState)))
 	BlkWithOutStateRoot, err := BlkWithOutState.Block.HashTreeRoot()
 	require.NoError(t, err)

-	BlkWithStateBadAtt := testutil.NewBeaconBlock()
+	BlkWithStateBadAtt := util.NewBeaconBlock()
 	BlkWithStateBadAtt.Block.Slot = 1
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(BlkWithStateBadAtt)))
 	BlkWithStateBadAttRoot, err := BlkWithStateBadAtt.Block.HashTreeRoot()
 	require.NoError(t, err)

-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, s.SetSlot(100*params.BeaconConfig().SlotsPerEpoch))
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, BlkWithStateBadAttRoot))

-	BlkWithValidState := testutil.NewBeaconBlock()
+	BlkWithValidState := util.NewBeaconBlock()
 	BlkWithValidState.Block.Slot = 2
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(BlkWithValidState)))

 	BlkWithValidStateRoot, err := BlkWithValidState.Block.HashTreeRoot()
 	require.NoError(t, err)
-	s, err = testutil.NewBeaconState()
+	s, err = util.NewBeaconState()
 	require.NoError(t, err)
 	err = s.SetFork(&ethpb.Fork{
 		Epoch:           0,
@@ -75,17 +77,17 @@ func TestStore_OnAttestation_ErrorConditions(t *testing.T) {
 	}{
 		{
 			name:      "attestation's data slot not aligned with target vote",
-			a:         testutil.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Slot: params.BeaconConfig().SlotsPerEpoch, Target: &ethpb.Checkpoint{Root: make([]byte, 32)}}}),
+			a:         util.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Slot: params.BeaconConfig().SlotsPerEpoch, Target: &ethpb.Checkpoint{Root: make([]byte, 32)}}}),
 			wantedErr: "slot 32 does not match target epoch 0",
 		},
 		{
 			name:      "no pre state for attestations's target block",
-			a:         testutil.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Target: &ethpb.Checkpoint{Root: BlkWithOutStateRoot[:]}}}),
+			a:         util.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Target: &ethpb.Checkpoint{Root: BlkWithOutStateRoot[:]}}}),
 			wantedErr: "could not get pre state for epoch 0",
 		},
 		{
 			name: "process attestation doesn't match current epoch",
-			a: testutil.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Slot: 100 * params.BeaconConfig().SlotsPerEpoch, Target: &ethpb.Checkpoint{Epoch: 100,
+			a: util.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Slot: 100 * params.BeaconConfig().SlotsPerEpoch, Target: &ethpb.Checkpoint{Epoch: 100,
 				Root: BlkWithStateBadAttRoot[:]}}}),
 			wantedErr: "target epoch 100 does not match current epoch",
 		},
@@ -103,9 +105,9 @@ func TestStore_OnAttestation_ErrorConditions(t *testing.T) {
 			name: "process nil field (a.Target) in attestation",
 			a: &ethpb.Attestation{
 				Data: &ethpb.AttestationData{
-					BeaconBlockRoot: make([]byte, 32),
+					BeaconBlockRoot: make([]byte, fieldparams.RootLength),
 					Target:          nil,
-					Source:          &ethpb.Checkpoint{Root: make([]byte, 32)},
+					Source:          &ethpb.Checkpoint{Root: make([]byte, fieldparams.RootLength)},
 				},
 				AggregationBits: make([]byte, 1),
 				Signature:       make([]byte, 96),
@@ -116,7 +118,7 @@ func TestStore_OnAttestation_ErrorConditions(t *testing.T) {

 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			err := service.onAttestation(ctx, tt.a)
+			err := service.OnAttestation(ctx, tt.a)
 			if tt.wantedErr != "" {
 				assert.ErrorContains(t, tt.wantedErr, err)
 			} else {
@@ -126,49 +128,182 @@ func TestStore_OnAttestation_ErrorConditions(t *testing.T) {
 	}
 }

-func TestStore_OnAttestation_Ok(t *testing.T) {
+func TestStore_OnAttestation_ErrorConditions_DoublyLinkedTree(t *testing.T) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{
-		BeaconDB:        beaconDB,
-		ForkChoiceStore: protoarray.New(0, 0, [32]byte{}),
-		StateGen:        stategen.New(beaconDB),
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithForkChoiceStore(doublylinkedtree.New(0, 0)),
+		WithStateGen(stategen.New(beaconDB)),
 	}
-	service, err := NewService(ctx, cfg)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)
-	genesisState, pks := testutil.DeterministicGenesisState(t, 64)
-	require.NoError(t, genesisState.SetGenesisTime(uint64(time.Now().Unix())-params.BeaconConfig().SecondsPerSlot))
+
+	_, err = blockTree1(t, beaconDB, []byte{'g'})
+	require.NoError(t, err)
+
+	BlkWithOutState := util.NewBeaconBlock()
+	BlkWithOutState.Block.Slot = 0
+	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(BlkWithOutState)))
+	BlkWithOutStateRoot, err := BlkWithOutState.Block.HashTreeRoot()
+	require.NoError(t, err)
+
+	BlkWithStateBadAtt := util.NewBeaconBlock()
+	BlkWithStateBadAtt.Block.Slot = 1
+	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(BlkWithStateBadAtt)))
+	BlkWithStateBadAttRoot, err := BlkWithStateBadAtt.Block.HashTreeRoot()
+	require.NoError(t, err)
+
+	s, err := util.NewBeaconState()
+	require.NoError(t, err)
+	require.NoError(t, s.SetSlot(100*params.BeaconConfig().SlotsPerEpoch))
+	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, BlkWithStateBadAttRoot))
+
+	BlkWithValidState := util.NewBeaconBlock()
+	BlkWithValidState.Block.Slot = 2
+	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(BlkWithValidState)))
+
+	BlkWithValidStateRoot, err := BlkWithValidState.Block.HashTreeRoot()
+	require.NoError(t, err)
+	s, err = util.NewBeaconState()
+	require.NoError(t, err)
+	err = s.SetFork(&ethpb.Fork{
+		Epoch:           0,
+		CurrentVersion:  params.BeaconConfig().GenesisForkVersion,
+		PreviousVersion: params.BeaconConfig().GenesisForkVersion,
+	})
+	require.NoError(t, err)
+	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, BlkWithValidStateRoot))
+
+	tests := []struct {
+		name      string
+		a         *ethpb.Attestation
+		wantedErr string
+	}{
+		{
+			name:      "attestation's data slot not aligned with target vote",
+			a:         util.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Slot: params.BeaconConfig().SlotsPerEpoch, Target: &ethpb.Checkpoint{Root: make([]byte, 32)}}}),
+			wantedErr: "slot 32 does not match target epoch 0",
+		},
+		{
+			name:      "no pre state for attestations's target block",
+			a:         util.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Target: &ethpb.Checkpoint{Root: BlkWithOutStateRoot[:]}}}),
+			wantedErr: "could not get pre state for epoch 0",
+		},
+		{
+			name: "process attestation doesn't match current epoch",
+			a: util.HydrateAttestation(&ethpb.Attestation{Data: &ethpb.AttestationData{Slot: 100 * params.BeaconConfig().SlotsPerEpoch, Target: &ethpb.Checkpoint{Epoch: 100,
+				Root: BlkWithStateBadAttRoot[:]}}}),
+			wantedErr: "target epoch 100 does not match current epoch",
+		},
+		{
+			name:      "process nil attestation",
+			a:         nil,
+			wantedErr: "attestation can't be nil",
+		},
+		{
+			name:      "process nil field (a.Data) in attestation",
+			a:         &ethpb.Attestation{},
+			wantedErr: "attestation's data can't be nil",
+		},
+		{
+			name: "process nil field (a.Target) in attestation",
+			a: &ethpb.Attestation{
+				Data: &ethpb.AttestationData{
+					BeaconBlockRoot: make([]byte, fieldparams.RootLength),
+					Target:          nil,
+					Source:          &ethpb.Checkpoint{Root: make([]byte, fieldparams.RootLength)},
+				},
+				AggregationBits: make([]byte, 1),
+				Signature:       make([]byte, 96),
+			},
+			wantedErr: "attestation's target can't be nil",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			err := service.OnAttestation(ctx, tt.a)
+			if tt.wantedErr != "" {
+				assert.ErrorContains(t, tt.wantedErr, err)
+			} else {
+				assert.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestStore_OnAttestation_Ok_ProtoArray(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+	genesisState, pks := util.DeterministicGenesisState(t, 64)
+	service.SetGenesisTime(time.Unix(time.Now().Unix()-int64(params.BeaconConfig().SecondsPerSlot), 0))
 	require.NoError(t, service.saveGenesisData(ctx, genesisState))
-	att, err := testutil.GenerateAttestations(genesisState, pks, 1, 0, false)
+	att, err := util.GenerateAttestations(genesisState, pks, 1, 0, false)
 	require.NoError(t, err)
 	tRoot := bytesutil.ToBytes32(att[0].Data.Target.Root)
 	copied := genesisState.Copy()
 	copied, err = transition.ProcessSlots(ctx, copied, 1)
 	require.NoError(t, err)
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, copied, tRoot))
-	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, 0, tRoot, tRoot, tRoot, 1, 1))
-	require.NoError(t, service.onAttestation(ctx, att[0]))
+	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, 0, tRoot, tRoot, 1, 1, false))
+	require.NoError(t, service.OnAttestation(ctx, att[0]))
+}
+
+func TestStore_OnAttestation_Ok_DoublyLinkedTree(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+
+	fcs := doublylinkedtree.New(0, 0)
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+	genesisState, pks := util.DeterministicGenesisState(t, 64)
+	service.SetGenesisTime(time.Unix(time.Now().Unix()-int64(params.BeaconConfig().SecondsPerSlot), 0))
+	require.NoError(t, service.saveGenesisData(ctx, genesisState))
+	att, err := util.GenerateAttestations(genesisState, pks, 1, 0, false)
+	require.NoError(t, err)
+	tRoot := bytesutil.ToBytes32(att[0].Data.Target.Root)
+	copied := genesisState.Copy()
+	copied, err = transition.ProcessSlots(ctx, copied, 1)
+	require.NoError(t, err)
+	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, copied, tRoot))
+	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, 0, tRoot, tRoot, 1, 1, false))
+	require.NoError(t, service.OnAttestation(ctx, att[0]))
 }

 func TestStore_SaveCheckpointState(t *testing.T) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{
-		BeaconDB: beaconDB,
-		StateGen: stategen.New(beaconDB),
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
 	}
-	service, err := NewService(ctx, cfg)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
-	err = s.SetFinalizedCheckpoint(&ethpb.Checkpoint{Root: bytesutil.PadTo([]byte{'A'}, 32)})
+	err = s.SetFinalizedCheckpoint(&ethpb.Checkpoint{Root: bytesutil.PadTo([]byte{'A'}, fieldparams.RootLength)})
 	require.NoError(t, err)
 	val := &ethpb.Validator{
 		PublicKey:             bytesutil.PadTo([]byte("foo"), 48),
-		WithdrawalCredentials: bytesutil.PadTo([]byte("bar"), 32),
+		WithdrawalCredentials: bytesutil.PadTo([]byte("bar"), fieldparams.RootLength),
 	}
 	err = s.SetValidators([]*ethpb.Validator{val})
 	require.NoError(t, err)
@@ -177,23 +312,23 @@ func TestStore_SaveCheckpointState(t *testing.T) {
 	r := [32]byte{'g'}
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, r))

-	service.justifiedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.bestJustifiedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.finalizedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.prevFinalizedCheckpt = &ethpb.Checkpoint{Root: r[:]}
+	service.store.SetJustifiedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetBestJustifiedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetPrevFinalizedCheckpt(&ethpb.Checkpoint{Root: r[:]})

 	r = bytesutil.ToBytes32([]byte{'A'})
-	cp1 := &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'A'}, 32)}
+	cp1 := &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'A'}, fieldparams.RootLength)}
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, bytesutil.ToBytes32([]byte{'A'})))
-	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{Root: bytesutil.PadTo([]byte{'A'}, 32)}))
+	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{Root: bytesutil.PadTo([]byte{'A'}, fieldparams.RootLength)}))

 	s1, err := service.getAttPreState(ctx, cp1)
 	require.NoError(t, err)
 	assert.Equal(t, 1*params.BeaconConfig().SlotsPerEpoch, s1.Slot(), "Unexpected state slot")

-	cp2 := &ethpb.Checkpoint{Epoch: 2, Root: bytesutil.PadTo([]byte{'B'}, 32)}
+	cp2 := &ethpb.Checkpoint{Epoch: 2, Root: bytesutil.PadTo([]byte{'B'}, fieldparams.RootLength)}
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, bytesutil.ToBytes32([]byte{'B'})))
-	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{Root: bytesutil.PadTo([]byte{'B'}, 32)}))
+	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{Root: bytesutil.PadTo([]byte{'B'}, fieldparams.RootLength)}))
 	s2, err := service.getAttPreState(ctx, cp2)
 	require.NoError(t, err)
 	assert.Equal(t, 2*params.BeaconConfig().SlotsPerEpoch, s2.Slot(), "Unexpected state slot")
@@ -211,13 +346,13 @@ func TestStore_SaveCheckpointState(t *testing.T) {
 	assert.Equal(t, 2*params.BeaconConfig().SlotsPerEpoch, s2.Slot(), "Unexpected state slot")

 	require.NoError(t, s.SetSlot(params.BeaconConfig().SlotsPerEpoch+1))
-	service.justifiedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.bestJustifiedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.finalizedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	service.prevFinalizedCheckpt = &ethpb.Checkpoint{Root: r[:]}
-	cp3 := &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'C'}, 32)}
+	service.store.SetJustifiedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetBestJustifiedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	service.store.SetPrevFinalizedCheckpt(&ethpb.Checkpoint{Root: r[:]})
+	cp3 := &ethpb.Checkpoint{Epoch: 1, Root: bytesutil.PadTo([]byte{'C'}, fieldparams.RootLength)}
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, s, bytesutil.ToBytes32([]byte{'C'})))
-	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{Root: bytesutil.PadTo([]byte{'C'}, 32)}))
+	require.NoError(t, service.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{Root: bytesutil.PadTo([]byte{'C'}, fieldparams.RootLength)}))
 	s3, err := service.getAttPreState(ctx, cp3)
 	require.NoError(t, err)
 	assert.Equal(t, s.Slot(), s3.Slot(), "Unexpected state slot")
@@ -227,16 +362,16 @@ func TestStore_UpdateCheckpointState(t *testing.T) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{
-		BeaconDB: beaconDB,
-		StateGen: stategen.New(beaconDB),
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
 	}
-	service, err := NewService(ctx, cfg)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

 	epoch := types.Epoch(1)
-	baseState, _ := testutil.DeterministicGenesisState(t, 1)
-	checkpoint := &ethpb.Checkpoint{Epoch: epoch, Root: bytesutil.PadTo([]byte("hi"), 32)}
+	baseState, _ := util.DeterministicGenesisState(t, 1)
+	checkpoint := &ethpb.Checkpoint{Epoch: epoch, Root: bytesutil.PadTo([]byte("hi"), fieldparams.RootLength)}
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, baseState, bytesutil.ToBytes32(checkpoint.Root)))
 	returned, err := service.getAttPreState(ctx, checkpoint)
 	require.NoError(t, err)
@@ -247,11 +382,11 @@ func TestStore_UpdateCheckpointState(t *testing.T) {
 	assert.Equal(t, returned.Slot(), cached.Slot(), "State should have been cached")

 	epoch = 2
-	newCheckpoint := &ethpb.Checkpoint{Epoch: epoch, Root: bytesutil.PadTo([]byte("bye"), 32)}
+	newCheckpoint := &ethpb.Checkpoint{Epoch: epoch, Root: bytesutil.PadTo([]byte("bye"), fieldparams.RootLength)}
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, baseState, bytesutil.ToBytes32(newCheckpoint.Root)))
 	returned, err = service.getAttPreState(ctx, newCheckpoint)
 	require.NoError(t, err)
-	s, err := core.StartSlot(newCheckpoint.Epoch)
+	s, err := slots.EpochStart(newCheckpoint.Epoch)
 	require.NoError(t, err)
 	baseState, err = transition.ProcessSlots(ctx, baseState, s)
 	require.NoError(t, err)
@@ -264,62 +399,44 @@ func TestStore_UpdateCheckpointState(t *testing.T) {

 func TestAttEpoch_MatchPrevEpoch(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
-
-	cfg := &Config{BeaconDB: beaconDB}
-	service, err := NewService(ctx, cfg)
-	require.NoError(t, err)

 	nowTime := uint64(params.BeaconConfig().SlotsPerEpoch) * params.BeaconConfig().SecondsPerSlot
-	require.NoError(t, service.verifyAttTargetEpoch(ctx, 0, nowTime, &ethpb.Checkpoint{Root: make([]byte, 32)}))
+	require.NoError(t, verifyAttTargetEpoch(ctx, 0, nowTime, &ethpb.Checkpoint{Root: make([]byte, fieldparams.RootLength)}))
 }

 func TestAttEpoch_MatchCurrentEpoch(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
-
-	cfg := &Config{BeaconDB: beaconDB}
-	service, err := NewService(ctx, cfg)
-	require.NoError(t, err)

 	nowTime := uint64(params.BeaconConfig().SlotsPerEpoch) * params.BeaconConfig().SecondsPerSlot
-	require.NoError(t, service.verifyAttTargetEpoch(ctx, 0, nowTime, &ethpb.Checkpoint{Epoch: 1}))
+	require.NoError(t, verifyAttTargetEpoch(ctx, 0, nowTime, &ethpb.Checkpoint{Epoch: 1}))
 }

 func TestAttEpoch_NotMatch(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
-
-	cfg := &Config{BeaconDB: beaconDB}
-	service, err := NewService(ctx, cfg)
-	require.NoError(t, err)

 	nowTime := 2 * uint64(params.BeaconConfig().SlotsPerEpoch) * params.BeaconConfig().SecondsPerSlot
-	err = service.verifyAttTargetEpoch(ctx, 0, nowTime, &ethpb.Checkpoint{Root: make([]byte, 32)})
+	err := verifyAttTargetEpoch(ctx, 0, nowTime, &ethpb.Checkpoint{Root: make([]byte, fieldparams.RootLength)})
 	assert.ErrorContains(t, "target epoch 0 does not match current epoch 2 or prev epoch 1", err)
 }

 func TestVerifyBeaconBlock_NoBlock(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
-
-	cfg := &Config{BeaconDB: beaconDB}
-	service, err := NewService(ctx, cfg)
+	opts := testServiceOptsWithDB(t)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	d := testutil.HydrateAttestationData(&ethpb.AttestationData{})
+	d := util.HydrateAttestationData(&ethpb.AttestationData{})
 	assert.ErrorContains(t, "signed beacon block can't be nil", service.verifyBeaconBlock(ctx, d))
 }

 func TestVerifyBeaconBlock_futureBlock(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{BeaconDB: beaconDB}
-	service, err := NewService(ctx, cfg)
+	opts := testServiceOptsWithDB(t)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b := testutil.NewBeaconBlock()
+	b := util.NewBeaconBlock()
 	b.Block.Slot = 2
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b)))
 	r, err := b.Block.HashTreeRoot()
@@ -331,13 +448,12 @@ func TestVerifyBeaconBlock_futureBlock(t *testing.T) {

 func TestVerifyBeaconBlock_OK(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{BeaconDB: beaconDB}
-	service, err := NewService(ctx, cfg)
+	opts := testServiceOptsWithDB(t)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b := testutil.NewBeaconBlock()
+	b := util.NewBeaconBlock()
 	b.Block.Slot = 2
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b)))
 	r, err := b.Block.HashTreeRoot()
@@ -347,23 +463,58 @@ func TestVerifyBeaconBlock_OK(t *testing.T) {
 	assert.NoError(t, service.verifyBeaconBlock(ctx, d), "Did not receive the wanted error")
 }

-func TestVerifyFinalizedConsistency_InconsistentRoot(t *testing.T) {
+func TestVerifyFinalizedConsistency_InconsistentRoot_ProtoArray(t *testing.T) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{BeaconDB: beaconDB, ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}
-	service, err := NewService(ctx, cfg)
+	fcs := protoarray.New(0, 0, [32]byte{'a'})
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b32 := testutil.NewBeaconBlock()
+	b32 := util.NewBeaconBlock()
 	b32.Block.Slot = 32
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b32)))
 	r32, err := b32.Block.HashTreeRoot()
 	require.NoError(t, err)

-	service.finalizedCheckpt = &ethpb.Checkpoint{Epoch: 1}
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 1})
+	b33 := util.NewBeaconBlock()
+	b33.Block.Slot = 33
+	b33.Block.ParentRoot = r32[:]
+	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b33)))
+	r33, err := b33.Block.HashTreeRoot()
+	require.NoError(t, err)

-	b33 := testutil.NewBeaconBlock()
+	err = service.VerifyFinalizedConsistency(context.Background(), r33[:])
+	require.ErrorContains(t, "Root and finalized store are not consistent", err)
+}
+
+func TestVerifyFinalizedConsistency_InconsistentRoot_DoublyLinkedTree(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+
+	fcs := doublylinkedtree.New(0, 0)
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithStateGen(stategen.New(beaconDB)),
+		WithForkChoiceStore(fcs),
+	}
+	service, err := NewService(ctx, opts...)
+	require.NoError(t, err)
+
+	b32 := util.NewBeaconBlock()
+	b32.Block.Slot = 32
+	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b32)))
+	r32, err := b32.Block.HashTreeRoot()
+	require.NoError(t, err)
+
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 1})
+	b33 := util.NewBeaconBlock()
 	b33.Block.Slot = 33
 	b33.Block.ParentRoot = r32[:]
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b33)))
@@ -376,21 +527,20 @@ func TestVerifyFinalizedConsistency_InconsistentRoot(t *testing.T) {

 func TestVerifyFinalizedConsistency_OK(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{BeaconDB: beaconDB, ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}
-	service, err := NewService(ctx, cfg)
+	opts := testServiceOptsWithDB(t)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b32 := testutil.NewBeaconBlock()
+	b32 := util.NewBeaconBlock()
 	b32.Block.Slot = 32
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b32)))
 	r32, err := b32.Block.HashTreeRoot()
 	require.NoError(t, err)

-	service.finalizedCheckpt = &ethpb.Checkpoint{Epoch: 1, Root: r32[:]}
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: r32[:], Epoch: 1})

-	b33 := testutil.NewBeaconBlock()
+	b33 := util.NewBeaconBlock()
 	b33.Block.Slot = 33
 	b33.Block.ParentRoot = r32[:]
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b33)))
@@ -403,27 +553,26 @@ func TestVerifyFinalizedConsistency_OK(t *testing.T) {

 func TestVerifyFinalizedConsistency_IsCanonical(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{BeaconDB: beaconDB, ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}
-	service, err := NewService(ctx, cfg)
+	opts := testServiceOptsWithDB(t)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b32 := testutil.NewBeaconBlock()
+	b32 := util.NewBeaconBlock()
 	b32.Block.Slot = 32
 	r32, err := b32.Block.HashTreeRoot()
 	require.NoError(t, err)

-	service.finalizedCheckpt = &ethpb.Checkpoint{Epoch: 1, Root: r32[:]}
+	service.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: r32[:], Epoch: 1})

-	b33 := testutil.NewBeaconBlock()
+	b33 := util.NewBeaconBlock()
 	b33.Block.Slot = 33
 	b33.Block.ParentRoot = r32[:]
 	r33, err := b33.Block.HashTreeRoot()
 	require.NoError(t, err)

-	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, b32.Block.Slot, r32, [32]byte{}, [32]byte{}, 0, 0))
-	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, b33.Block.Slot, r33, r32, [32]byte{}, 0, 0))
+	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, b32.Block.Slot, r32, [32]byte{}, 0, 0, false))
+	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, b33.Block.Slot, r33, r32, 0, 0, false))

 	_, err = service.cfg.ForkChoiceStore.Head(ctx, 0, r32, []uint64{}, 0)
 	require.NoError(t, err)
--- a/beacon-chain/blockchain/process_block.go
+++ b/beacon-chain/blockchain/process_block.go
@@ -6,20 +6,23 @@ import (
 	"time"

 	"github.com/pkg/errors"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/feed"
 	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	coreTime "github.com/prysmaticlabs/prysm/beacon-chain/core/time"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
 	"github.com/prysmaticlabs/prysm/config/features"
+	"github.com/prysmaticlabs/prysm/config/params"
 	"github.com/prysmaticlabs/prysm/crypto/bls"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	"github.com/prysmaticlabs/prysm/monitoring/tracing"
 	ethpbv1 "github.com/prysmaticlabs/prysm/proto/eth/v1"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/attestation"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/runtime/version"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	"go.opencensus.io/trace"
 )

@@ -86,9 +89,8 @@ var initialSyncBlockCacheSize = uint64(2 * params.BeaconConfig().SlotsPerEpoch)
 func (s *Service) onBlock(ctx context.Context, signed block.SignedBeaconBlock, blockRoot [32]byte) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.onBlock")
 	defer span.End()
-
-	if signed == nil || signed.IsNil() || signed.Block().IsNil() {
-		return errors.New("nil block")
+	if err := helpers.BeaconBlockIsNil(signed); err != nil {
+		return err
 	}
 	b := signed.Block()

@@ -97,64 +99,127 @@ func (s *Service) onBlock(ctx context.Context, signed block.SignedBeaconBlock, b
 		return err
 	}

+	preStateVersion, preStateHeader, err := getStateVersionAndPayload(preState)
+	if err != nil {
+		return err
+	}
 	postState, err := transition.ExecuteStateTransition(ctx, preState, signed)
 	if err != nil {
 		return err
 	}
-
-	if err := s.savePostStateInfo(ctx, blockRoot, signed, postState, false /* reg sync */); err != nil {
+	if err := s.notifyNewPayload(ctx, preStateVersion, preStateHeader, postState, signed); err != nil {
+		return errors.Wrap(err, "could not verify new payload")
+	}
+	// TODO(10261) Check optimistic status
+	if err := s.savePostStateInfo(ctx, blockRoot, signed, postState, false /* reg sync */, false /*optimistic sync*/); err != nil {
+		return err
+	}
+	if err := s.cfg.ForkChoiceStore.SetOptimisticToValid(ctx, blockRoot); err != nil {
+		return err
+	}
+	// We add a proposer score boost to fork choice for the block root if applicable, right after
+	// running a successful state transition for the block.
+	if err := s.cfg.ForkChoiceStore.BoostProposerRoot(
+		ctx, signed.Block().Slot(), blockRoot, s.genesisTime,
+	); err != nil {
 		return err
 	}

-	// Updating next slot state cache can happen in the background. It shouldn't block rest of the process.
-	if features.Get().EnableNextSlotStateCache {
+	// If slasher is configured, forward the attestations in the block via
+	// an event feed for processing.
+	if features.Get().EnableSlasher {
+		// Feed the indexed attestation to slasher if enabled. This action
+		// is done in the background to avoid adding more load to this critical code path.
 		go func() {
-			// Use a custom deadline here, since this method runs asynchronously.
-			// We ignore the parent method's context and instead create a new one
-			// with a custom deadline, therefore using the background context instead.
-			slotCtx, cancel := context.WithTimeout(context.Background(), slotDeadline)
-			defer cancel()
-			if err := transition.UpdateNextSlotCache(slotCtx, blockRoot[:], postState); err != nil {
-				log.WithError(err).Debug("could not update next slot state cache")
+			// Using a different context to prevent timeouts as this operation can be expensive
+			// and we want to avoid affecting the critical code path.
+			ctx := context.TODO()
+			for _, att := range signed.Block().Body().Attestations() {
+				committee, err := helpers.BeaconCommitteeFromState(ctx, preState, att.Data.Slot, att.Data.CommitteeIndex)
+				if err != nil {
+					log.WithError(err).Error("Could not get attestation committee")
+					tracing.AnnotateError(span, err)
+					return
+				}
+				indexedAtt, err := attestation.ConvertToIndexed(ctx, att, committee)
+				if err != nil {
+					log.WithError(err).Error("Could not convert to indexed attestation")
+					tracing.AnnotateError(span, err)
+					return
+				}
+				s.cfg.SlasherAttestationsFeed.Send(indexedAtt)
 			}
 		}()
 	}

 	// Update justified check point.
-	if postState.CurrentJustifiedCheckpoint().Epoch > s.justifiedCheckpt.Epoch {
+	justified := s.store.JustifiedCheckpt()
+	if justified == nil {
+		return errNilJustifiedInStore
+	}
+	currJustifiedEpoch := justified.Epoch
+	if postState.CurrentJustifiedCheckpoint().Epoch > currJustifiedEpoch {
 		if err := s.updateJustified(ctx, postState); err != nil {
 			return err
 		}
 	}

-	newFinalized := postState.FinalizedCheckpointEpoch() > s.finalizedCheckpt.Epoch
-	if features.Get().UpdateHeadTimely {
-		if newFinalized {
-			if err := s.finalizedImpliesNewJustified(ctx, postState); err != nil {
-				return errors.Wrap(err, "could not save new justified")
-			}
-			s.prevFinalizedCheckpt = s.finalizedCheckpt
-			s.finalizedCheckpt = postState.FinalizedCheckpoint()
-		}
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	newFinalized := postState.FinalizedCheckpointEpoch() > finalized.Epoch
+	if newFinalized {
+		s.store.SetPrevFinalizedCheckpt(finalized)
+		s.store.SetFinalizedCheckpt(postState.FinalizedCheckpoint())
+		s.store.SetPrevJustifiedCheckpt(justified)
+		s.store.SetJustifiedCheckpt(postState.CurrentJustifiedCheckpoint())
+	}

-		if err := s.updateHead(ctx, s.getJustifiedBalances()); err != nil {
-			log.WithError(err).Warn("Could not update head")
-		}
+	balances, err := s.justifiedBalances.get(ctx, bytesutil.ToBytes32(justified.Root))
+	if err != nil {
+		msg := fmt.Sprintf("could not read balances for state w/ justified checkpoint %#x", justified.Root)
+		return errors.Wrap(err, msg)
+	}
+	if err := s.updateHead(ctx, balances); err != nil {
+		log.WithError(err).Warn("Could not update head")
+	}
+	if _, err := s.notifyForkchoiceUpdate(ctx, s.headBlock().Block(), bytesutil.ToBytes32(finalized.Root)); err != nil {
+		return err
+	}

-		if err := s.pruneCanonicalAttsFromPool(ctx, blockRoot, signed); err != nil {
+	if err := s.pruneCanonicalAttsFromPool(ctx, blockRoot, signed); err != nil {
+		return err
+	}
+
+	// Send notification of the processed block to the state feed.
+	s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
+		Type: statefeed.BlockProcessed,
+		Data: &statefeed.BlockProcessedData{
+			Slot:        signed.Block().Slot(),
+			BlockRoot:   blockRoot,
+			SignedBlock: signed,
+			Verified:    true,
+		},
+	})
+
+	// Updating next slot state cache can happen in the background. It shouldn't block rest of the process.
+	go func() {
+		// Use a custom deadline here, since this method runs asynchronously.
+		// We ignore the parent method's context and instead create a new one
+		// with a custom deadline, therefore using the background context instead.
+		slotCtx, cancel := context.WithTimeout(context.Background(), slotDeadline)
+		defer cancel()
+		if err := transition.UpdateNextSlotCache(slotCtx, blockRoot[:], postState); err != nil {
+			log.WithError(err).Debug("could not update next slot state cache")
+		}
+	}()
+
+	// Save justified check point to db.
+	if postState.CurrentJustifiedCheckpoint().Epoch > currJustifiedEpoch {
+		if err := s.cfg.BeaconDB.SaveJustifiedCheckpoint(ctx, postState.CurrentJustifiedCheckpoint()); err != nil {
 			return err
 		}
-
-		// Send notification of the processed block to the state feed.
-		s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
-			Type: statefeed.BlockProcessed,
-			Data: &statefeed.BlockProcessedData{
-				Slot:        signed.Block().Slot(),
-				BlockRoot:   blockRoot,
-				SignedBlock: signed,
-				Verified:    true,
-			},
-		})
 	}

 	// Update finalized check point.
@@ -166,11 +231,6 @@ func (s *Service) onBlock(ctx context.Context, signed block.SignedBeaconBlock, b
 		if err := s.cfg.ForkChoiceStore.Prune(ctx, fRoot); err != nil {
 			return errors.Wrap(err, "could not prune proto array fork choice nodes")
 		}
-		if !features.Get().UpdateHeadTimely {
-			if err := s.finalizedImpliesNewJustified(ctx, postState); err != nil {
-				return errors.Wrap(err, "could not save new justified")
-			}
-		}
 		go func() {
 			// Send an event regarding the new finalized checkpoint over a common event feed.
 			s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
@@ -199,88 +259,116 @@ func (s *Service) onBlock(ctx context.Context, signed block.SignedBeaconBlock, b
 	return s.handleEpochBoundary(ctx, postState)
 }

+func getStateVersionAndPayload(preState state.BeaconState) (int, *ethpb.ExecutionPayloadHeader, error) {
+	var preStateHeader *ethpb.ExecutionPayloadHeader
+	var err error
+	preStateVersion := preState.Version()
+	switch preStateVersion {
+	case version.Phase0, version.Altair:
+	default:
+		preStateHeader, err = preState.LatestExecutionPayloadHeader()
+		if err != nil {
+			return 0, nil, err
+		}
+	}
+	return preStateVersion, preStateHeader, nil
+}
+
 func (s *Service) onBlockBatch(ctx context.Context, blks []block.SignedBeaconBlock,
-	blockRoots [][32]byte) ([]*ethpb.Checkpoint, []*ethpb.Checkpoint, error) {
+	blockRoots [][32]byte) ([]*ethpb.Checkpoint, []*ethpb.Checkpoint, []bool, error) {
 	ctx, span := trace.StartSpan(ctx, "blockChain.onBlockBatch")
 	defer span.End()

 	if len(blks) == 0 || len(blockRoots) == 0 {
-		return nil, nil, errors.New("no blocks provided")
+		return nil, nil, nil, errors.New("no blocks provided")
 	}
-	if blks[0] == nil || blks[0].IsNil() || blks[0].Block().IsNil() {
-		return nil, nil, errors.New("nil block")
+	if err := helpers.BeaconBlockIsNil(blks[0]); err != nil {
+		return nil, nil, nil, err
 	}
 	b := blks[0].Block()

 	// Retrieve incoming block's pre state.
 	if err := s.verifyBlkPreState(ctx, b); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	preState, err := s.cfg.StateGen.StateByRootInitialSync(ctx, bytesutil.ToBytes32(b.ParentRoot()))
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	if preState == nil || preState.IsNil() {
-		return nil, nil, fmt.Errorf("nil pre state for slot %d", b.Slot())
+		return nil, nil, nil, fmt.Errorf("nil pre state for slot %d", b.Slot())
 	}

 	jCheckpoints := make([]*ethpb.Checkpoint, len(blks))
 	fCheckpoints := make([]*ethpb.Checkpoint, len(blks))
-	sigSet := &bls.SignatureSet{
+	optimistic := make([]bool, len(blks))
+	sigSet := &bls.SignatureBatch{
 		Signatures: [][]byte{},
 		PublicKeys: []bls.PublicKey{},
 		Messages:   [][32]byte{},
 	}
-	var set *bls.SignatureSet
+	var set *bls.SignatureBatch
 	boundaries := make(map[[32]byte]state.BeaconState)
 	for i, b := range blks {
+		preStateVersion, preStateHeader, err := getStateVersionAndPayload(preState)
+		if err != nil {
+			return nil, nil, nil, err
+		}
 		set, preState, err = transition.ExecuteStateTransitionNoVerifyAnySig(ctx, preState, b)
 		if err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
+		if err := s.notifyNewPayload(ctx, preStateVersion, preStateHeader, preState, b); err != nil {
+			return nil, nil, nil, err
+		}
+
 		// Save potential boundary states.
-		if core.IsEpochStart(preState.Slot()) {
+		if slots.IsEpochStart(preState.Slot()) {
 			boundaries[blockRoots[i]] = preState.Copy()
 			if err := s.handleEpochBoundary(ctx, preState); err != nil {
-				return nil, nil, errors.Wrap(err, "could not handle epoch boundary state")
+				return nil, nil, nil, errors.Wrap(err, "could not handle epoch boundary state")
 			}
 		}
 		jCheckpoints[i] = preState.CurrentJustifiedCheckpoint()
 		fCheckpoints[i] = preState.FinalizedCheckpoint()
+
 		sigSet.Join(set)
 	}
 	verify, err := sigSet.Verify()
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	if !verify {
-		return nil, nil, errors.New("batch block signature verification failed")
+		return nil, nil, nil, errors.New("batch block signature verification failed")
 	}
 	for r, st := range boundaries {
 		if err := s.cfg.StateGen.SaveState(ctx, r, st); err != nil {
-			return nil, nil, err
+			return nil, nil, nil, err
 		}
 	}
 	// Also saves the last post state which to be used as pre state for the next batch.
 	lastB := blks[len(blks)-1]
 	lastBR := blockRoots[len(blockRoots)-1]
 	if err := s.cfg.StateGen.SaveState(ctx, lastBR, preState); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
 	if err := s.saveHeadNoDB(ctx, lastB, lastBR, preState); err != nil {
-		return nil, nil, err
+		return nil, nil, nil, err
 	}
-	return fCheckpoints, jCheckpoints, nil
+	return fCheckpoints, jCheckpoints, optimistic, nil
 }

 // handles a block after the block's batch has been verified, where we can save blocks
 // their state summaries and split them off to relative hot/cold storage.
 func (s *Service) handleBlockAfterBatchVerify(ctx context.Context, signed block.SignedBeaconBlock,
-	blockRoot [32]byte, fCheckpoint, jCheckpoint *ethpb.Checkpoint) error {
+	blockRoot [32]byte, fCheckpoint, jCheckpoint *ethpb.Checkpoint, optimistic bool) error {
 	b := signed.Block()

 	s.saveInitSyncBlock(blockRoot, signed)
-	if err := s.insertBlockToForkChoiceStore(ctx, b, blockRoot, fCheckpoint, jCheckpoint); err != nil {
+	if err := s.insertBlockToForkChoiceStore(ctx, b, blockRoot, fCheckpoint, jCheckpoint, optimistic); err != nil {
+		return err
+	}
+	if _, err := s.notifyForkchoiceUpdate(ctx, b, bytesutil.ToBytes32(fCheckpoint.Root)); err != nil {
 		return err
 	}
 	if err := s.cfg.BeaconDB.SaveStateSummary(ctx, &ethpb.StateSummary{
@@ -298,21 +386,27 @@ func (s *Service) handleBlockAfterBatchVerify(ctx context.Context, signed block.
 		s.clearInitSyncBlocks()
 	}

-	if jCheckpoint.Epoch > s.justifiedCheckpt.Epoch {
+	justified := s.store.JustifiedCheckpt()
+	if justified == nil {
+		return errNilJustifiedInStore
+	}
+	if jCheckpoint.Epoch > justified.Epoch {
 		if err := s.updateJustifiedInitSync(ctx, jCheckpoint); err != nil {
 			return err
 		}
 	}

+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
 	// Update finalized check point. Prune the block cache and helper caches on every new finalized epoch.
-	if fCheckpoint.Epoch > s.finalizedCheckpt.Epoch {
+	if fCheckpoint.Epoch > finalized.Epoch {
 		if err := s.updateFinalized(ctx, fCheckpoint); err != nil {
 			return err
 		}
-		if features.Get().UpdateHeadTimely {
-			s.prevFinalizedCheckpt = s.finalizedCheckpt
-			s.finalizedCheckpt = fCheckpoint
-		}
+		s.store.SetPrevFinalizedCheckpt(finalized)
+		s.store.SetFinalizedCheckpt(fCheckpoint)
 	}
 	return nil
 }
@@ -324,7 +418,7 @@ func (s *Service) handleEpochBoundary(ctx context.Context, postState state.Beaco

 	if postState.Slot()+1 == s.nextEpochBoundarySlot {
 		// Update caches for the next epoch at epoch boundary slot - 1.
-		if err := helpers.UpdateCommitteeCache(postState, core.NextEpoch(postState)); err != nil {
+		if err := helpers.UpdateCommitteeCache(postState, coreTime.NextEpoch(postState)); err != nil {
 			return err
 		}
 		copied := postState.Copy()
@@ -332,7 +426,7 @@ func (s *Service) handleEpochBoundary(ctx context.Context, postState state.Beaco
 		if err != nil {
 			return err
 		}
-		if err := helpers.UpdateProposerIndicesInCache(copied); err != nil {
+		if err := helpers.UpdateProposerIndicesInCache(ctx, copied); err != nil {
 			return err
 		}
 	} else if postState.Slot() >= s.nextEpochBoundarySlot {
@@ -340,17 +434,17 @@ func (s *Service) handleEpochBoundary(ctx context.Context, postState state.Beaco
 			return err
 		}
 		var err error
-		s.nextEpochBoundarySlot, err = core.StartSlot(core.NextEpoch(postState))
+		s.nextEpochBoundarySlot, err = slots.EpochStart(coreTime.NextEpoch(postState))
 		if err != nil {
 			return err
 		}

 		// Update caches at epoch boundary slot.
 		// The following updates have short cut to return nil cheaply if fulfilled during boundary slot - 1.
-		if err := helpers.UpdateCommitteeCache(postState, core.CurrentEpoch(postState)); err != nil {
+		if err := helpers.UpdateCommitteeCache(postState, coreTime.CurrentEpoch(postState)); err != nil {
 			return err
 		}
-		if err := helpers.UpdateProposerIndicesInCache(postState); err != nil {
+		if err := helpers.UpdateProposerIndicesInCache(ctx, postState); err != nil {
 			return err
 		}
 	}
@@ -361,18 +455,18 @@ func (s *Service) handleEpochBoundary(ctx context.Context, postState state.Beaco
 // This feeds in the block and block's attestations to fork choice store. It's allows fork choice store
 // to gain information on the most current chain.
 func (s *Service) insertBlockAndAttestationsToForkChoiceStore(ctx context.Context, blk block.BeaconBlock, root [32]byte,
-	st state.BeaconState) error {
+	st state.BeaconState, optimistic bool) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.insertBlockAndAttestationsToForkChoiceStore")
 	defer span.End()

 	fCheckpoint := st.FinalizedCheckpoint()
 	jCheckpoint := st.CurrentJustifiedCheckpoint()
-	if err := s.insertBlockToForkChoiceStore(ctx, blk, root, fCheckpoint, jCheckpoint); err != nil {
+	if err := s.insertBlockToForkChoiceStore(ctx, blk, root, fCheckpoint, jCheckpoint, optimistic); err != nil {
 		return err
 	}
 	// Feed in block's attestations to fork choice store.
 	for _, a := range blk.Body().Attestations() {
-		committee, err := helpers.BeaconCommitteeFromState(st, a.Data.Slot, a.Data.CommitteeIndex)
+		committee, err := helpers.BeaconCommitteeFromState(ctx, st, a.Data.Slot, a.Data.CommitteeIndex)
 		if err != nil {
 			return err
 		}
@@ -386,15 +480,16 @@ func (s *Service) insertBlockAndAttestationsToForkChoiceStore(ctx context.Contex
 }

 func (s *Service) insertBlockToForkChoiceStore(ctx context.Context, blk block.BeaconBlock,
-	root [32]byte, fCheckpoint, jCheckpoint *ethpb.Checkpoint) error {
+	root [32]byte, fCheckpoint, jCheckpoint *ethpb.Checkpoint, optimistic bool) error {
+	//TODO(10261) check if the blocks are optimistic or not when filling fork choice
 	if err := s.fillInForkChoiceMissingBlocks(ctx, blk, fCheckpoint, jCheckpoint); err != nil {
 		return err
 	}
 	// Feed in block to fork choice store.
 	if err := s.cfg.ForkChoiceStore.ProcessBlock(ctx,
-		blk.Slot(), root, bytesutil.ToBytes32(blk.ParentRoot()), bytesutil.ToBytes32(blk.Body().Graffiti()),
+		blk.Slot(), root, bytesutil.ToBytes32(blk.ParentRoot()),
 		jCheckpoint.Epoch,
-		fCheckpoint.Epoch); err != nil {
+		fCheckpoint.Epoch, optimistic); err != nil {
 		return errors.Wrap(err, "could not process block for proto array fork choice")
 	}
 	return nil
@@ -402,7 +497,7 @@ func (s *Service) insertBlockToForkChoiceStore(ctx context.Context, blk block.Be

 // This saves post state info to DB or cache. This also saves post state info to fork choice store.
 // Post state info consists of processed block and state. Do not call this method unless the block and state are verified.
-func (s *Service) savePostStateInfo(ctx context.Context, r [32]byte, b block.SignedBeaconBlock, st state.BeaconState, initSync bool) error {
+func (s *Service) savePostStateInfo(ctx context.Context, r [32]byte, b block.SignedBeaconBlock, st state.BeaconState, initSync bool, optimistic bool) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.savePostStateInfo")
 	defer span.End()
 	if initSync {
@@ -413,7 +508,7 @@ func (s *Service) savePostStateInfo(ctx context.Context, r [32]byte, b block.Sig
 	if err := s.cfg.StateGen.SaveState(ctx, r, st); err != nil {
 		return errors.Wrap(err, "could not save state")
 	}
-	if err := s.insertBlockAndAttestationsToForkChoiceStore(ctx, b.Block(), r, st); err != nil {
+	if err := s.insertBlockAndAttestationsToForkChoiceStore(ctx, b.Block(), r, st, optimistic); err != nil {
 		return errors.Wrapf(err, "could not insert block %d to fork choice store", b.Block().Slot())
 	}
 	return nil
--- a/beacon-chain/blockchain/process_block_helpers.go
+++ b/beacon-chain/blockchain/process_block_helpers.go
@@ -7,22 +7,20 @@ import (

 	"github.com/pkg/errors"
 	types "github.com/prysmaticlabs/eth2-types"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
-	"github.com/prysmaticlabs/prysm/config/features"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	"github.com/prysmaticlabs/prysm/monitoring/tracing"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/attestation"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	"go.opencensus.io/trace"
 )

 // CurrentSlot returns the current slot based on time.
 func (s *Service) CurrentSlot() types.Slot {
-	return core.CurrentSlot(uint64(s.genesisTime.Unix()))
+	return slots.CurrentSlot(uint64(s.genesisTime.Unix()))
 }

 // getBlockPreState returns the pre state of an incoming block. It uses the parent root of the block
@@ -46,7 +44,7 @@ func (s *Service) getBlockPreState(ctx context.Context, b block.BeaconBlock) (st
 	}

 	// Verify block slot time is not from the future.
-	if err := core.VerifySlotTime(preState.GenesisTime(), b.Slot(), params.BeaconNetworkConfig().MaximumGossipClockDisparity); err != nil {
+	if err := slots.VerifyTime(uint64(s.genesisTime.Unix()), b.Slot(), params.BeaconNetworkConfig().MaximumGossipClockDisparity); err != nil {
 		return nil, err
 	}

@@ -93,7 +91,11 @@ func (s *Service) verifyBlkPreState(ctx context.Context, b block.BeaconBlock) er
 func (s *Service) VerifyBlkDescendant(ctx context.Context, root [32]byte) error {
 	ctx, span := trace.StartSpan(ctx, "blockChain.VerifyBlkDescendant")
 	defer span.End()
-	fRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(s.finalizedCheckpt.Root))
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	fRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(finalized.Root))
 	finalizedBlkSigned, err := s.cfg.BeaconDB.Block(ctx, fRoot)
 	if err != nil {
 		return err
@@ -111,7 +113,7 @@ func (s *Service) VerifyBlkDescendant(ctx context.Context, root [32]byte) error
 	}

 	if !bytes.Equal(bFinalizedRoot, fRoot[:]) {
-		err := fmt.Errorf("block %#x is not a descendent of the current finalized block slot %d, %#x != %#x",
+		err := fmt.Errorf("block %#x is not a descendant of the current finalized block slot %d, %#x != %#x",
 			bytesutil.Trunc(root[:]), finalizedBlk.Slot(), bytesutil.Trunc(bFinalizedRoot),
 			bytesutil.Trunc(fRoot[:]))
 		tracing.AnnotateError(span, err)
@@ -123,7 +125,11 @@ func (s *Service) VerifyBlkDescendant(ctx context.Context, root [32]byte) error
 // verifyBlkFinalizedSlot validates input block is not less than or equal
 // to current finalized slot.
 func (s *Service) verifyBlkFinalizedSlot(b block.BeaconBlock) error {
-	finalizedSlot, err := core.StartSlot(s.finalizedCheckpt.Epoch)
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	finalizedSlot, err := slots.EpochStart(finalized.Epoch)
 	if err != nil {
 		return err
 	}
@@ -136,59 +142,45 @@ func (s *Service) verifyBlkFinalizedSlot(b block.BeaconBlock) error {
 // shouldUpdateCurrentJustified prevents bouncing attack, by only update conflicting justified
 // checkpoints in the fork choice if in the early slots of the epoch.
 // Otherwise, delay incorporation of new justified checkpoint until next epoch boundary.
-// See https://ethresear.ch/t/prevention-of-bouncing-attack-on-ffg/6114 for more detailed analysis and discussion.
+//
+// Spec code:
+// def should_update_justified_checkpoint(store: Store, new_justified_checkpoint: Checkpoint) -> bool:
+//    """
+//    To address the bouncing attack, only update conflicting justified
+//    checkpoints in the fork choice if in the early slots of the epoch.
+//    Otherwise, delay incorporation of new justified checkpoint until next epoch boundary.
+//
+//    See https://ethresear.ch/t/prevention-of-bouncing-attack-on-ffg/6114 for more detailed analysis and discussion.
+//    """
+//    if compute_slots_since_epoch_start(get_current_slot(store)) < SAFE_SLOTS_TO_UPDATE_JUSTIFIED:
+//        return True
+//
+//    justified_slot = compute_start_slot_at_epoch(store.justified_checkpoint.epoch)
+//    if not get_ancestor(store, new_justified_checkpoint.root, justified_slot) == store.justified_checkpoint.root:
+//        return False
+//
+//    return True
 func (s *Service) shouldUpdateCurrentJustified(ctx context.Context, newJustifiedCheckpt *ethpb.Checkpoint) (bool, error) {
 	ctx, span := trace.StartSpan(ctx, "blockChain.shouldUpdateCurrentJustified")
 	defer span.End()

-	if core.SlotsSinceEpochStarts(s.CurrentSlot()) < params.BeaconConfig().SafeSlotsToUpdateJustified {
+	if slots.SinceEpochStarts(s.CurrentSlot()) < params.BeaconConfig().SafeSlotsToUpdateJustified {
 		return true, nil
 	}
-	var newJustifiedBlockSigned block.SignedBeaconBlock
+	justified := s.store.JustifiedCheckpt()
+	jSlot, err := slots.EpochStart(justified.Epoch)
+	if err != nil {
+		return false, err
+	}
 	justifiedRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(newJustifiedCheckpt.Root))
-	var err error
-	if s.hasInitSyncBlock(justifiedRoot) {
-		newJustifiedBlockSigned = s.getInitSyncBlock(justifiedRoot)
-	} else {
-		newJustifiedBlockSigned, err = s.cfg.BeaconDB.Block(ctx, justifiedRoot)
-		if err != nil {
-			return false, err
-		}
-	}
-	if newJustifiedBlockSigned == nil || newJustifiedBlockSigned.IsNil() || newJustifiedBlockSigned.Block().IsNil() {
-		return false, errors.New("nil new justified block")
-	}
-
-	newJustifiedBlock := newJustifiedBlockSigned.Block()
-	jSlot, err := core.StartSlot(s.justifiedCheckpt.Epoch)
+	b, err := s.ancestor(ctx, justifiedRoot[:], jSlot)
 	if err != nil {
 		return false, err
 	}
-	if newJustifiedBlock.Slot() <= jSlot {
+	if !bytes.Equal(b, justified.Root) {
 		return false, nil
 	}
-	var justifiedBlockSigned block.SignedBeaconBlock
-	cachedJustifiedRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(s.justifiedCheckpt.Root))
-	if s.hasInitSyncBlock(cachedJustifiedRoot) {
-		justifiedBlockSigned = s.getInitSyncBlock(cachedJustifiedRoot)
-	} else {
-		justifiedBlockSigned, err = s.cfg.BeaconDB.Block(ctx, cachedJustifiedRoot)
-		if err != nil {
-			return false, err
-		}
-	}

-	if justifiedBlockSigned == nil || justifiedBlockSigned.IsNil() || justifiedBlockSigned.Block().IsNil() {
-		return false, errors.New("nil justified block")
-	}
-	justifiedBlock := justifiedBlockSigned.Block()
-	b, err := s.ancestor(ctx, justifiedRoot[:], justifiedBlock.Slot())
-	if err != nil {
-		return false, err
-	}
-	if !bytes.Equal(b, s.justifiedCheckpt.Root) {
-		return false, nil
-	}
 	return true, nil
 }

@@ -197,8 +189,12 @@ func (s *Service) updateJustified(ctx context.Context, state state.ReadOnlyBeaco
 	defer span.End()

 	cpt := state.CurrentJustifiedCheckpoint()
-	if cpt.Epoch > s.bestJustifiedCheckpt.Epoch {
-		s.bestJustifiedCheckpt = cpt
+	bestJustified := s.store.BestJustifiedCheckpt()
+	if bestJustified == nil {
+		return errNilBestJustifiedInStore
+	}
+	if cpt.Epoch > bestJustified.Epoch {
+		s.store.SetBestJustifiedCheckpt(cpt)
 	}
 	canUpdate, err := s.shouldUpdateCurrentJustified(ctx, cpt)
 	if err != nil {
@@ -206,27 +202,33 @@ func (s *Service) updateJustified(ctx context.Context, state state.ReadOnlyBeaco
 	}

 	if canUpdate {
-		s.prevJustifiedCheckpt = s.justifiedCheckpt
-		s.justifiedCheckpt = cpt
-		if err := s.cacheJustifiedStateBalances(ctx, bytesutil.ToBytes32(s.justifiedCheckpt.Root)); err != nil {
-			return err
+		justified := s.store.JustifiedCheckpt()
+		if justified == nil {
+			return errNilJustifiedInStore
 		}
+		s.store.SetPrevJustifiedCheckpt(justified)
+		s.store.SetJustifiedCheckpt(cpt)
 	}

-	return s.cfg.BeaconDB.SaveJustifiedCheckpoint(ctx, cpt)
+	return nil
 }

 // This caches input checkpoint as justified for the service struct. It rotates current justified to previous justified,
 // caches justified checkpoint balances for fork choice and save justified checkpoint in DB.
 // This method does not have defense against fork choice bouncing attack, which is why it's only recommend to be used during initial syncing.
 func (s *Service) updateJustifiedInitSync(ctx context.Context, cp *ethpb.Checkpoint) error {
-	s.prevJustifiedCheckpt = s.justifiedCheckpt
-	s.justifiedCheckpt = cp
-	if err := s.cacheJustifiedStateBalances(ctx, bytesutil.ToBytes32(s.justifiedCheckpt.Root)); err != nil {
+	justified := s.store.JustifiedCheckpt()
+	if justified == nil {
+		return errNilJustifiedInStore
+	}
+	s.store.SetPrevJustifiedCheckpt(justified)
+
+	if err := s.cfg.BeaconDB.SaveJustifiedCheckpoint(ctx, cp); err != nil {
 		return err
 	}
+	s.store.SetJustifiedCheckpt(cp)

-	return s.cfg.BeaconDB.SaveJustifiedCheckpoint(ctx, cp)
+	return nil
 }

 func (s *Service) updateFinalized(ctx context.Context, cp *ethpb.Checkpoint) error {
@@ -243,10 +245,6 @@ func (s *Service) updateFinalized(ctx context.Context, cp *ethpb.Checkpoint) err
 	if err := s.cfg.BeaconDB.SaveFinalizedCheckpoint(ctx, cp); err != nil {
 		return err
 	}
-	if !features.Get().UpdateHeadTimely {
-		s.prevFinalizedCheckpt = s.finalizedCheckpt
-		s.finalizedCheckpt = cp
-	}

 	fRoot := bytesutil.ToBytes32(cp.Root)
 	if err := s.cfg.StateGen.MigrateToCold(ctx, fRoot); err != nil {
@@ -329,49 +327,6 @@ func (s *Service) ancestorByDB(ctx context.Context, r [32]byte, slot types.Slot)
 	return s.ancestorByDB(ctx, bytesutil.ToBytes32(b.ParentRoot()), slot)
 }

-// This updates justified check point in store, if the new justified is later than stored justified or
-// the store's justified is not in chain with finalized check point.
-//
-// Spec definition:
-//   # Potentially update justified if different from store
-//        if store.justified_checkpoint != state.current_justified_checkpoint:
-//            # Update justified if new justified is later than store justified
-//            if state.current_justified_checkpoint.epoch > store.justified_checkpoint.epoch:
-//                store.justified_checkpoint = state.current_justified_checkpoint
-//                return
-//            # Update justified if store justified is not in chain with finalized checkpoint
-//            finalized_slot = compute_start_slot_at_epoch(store.finalized_checkpoint.epoch)
-//            ancestor_at_finalized_slot = get_ancestor(store, store.justified_checkpoint.root, finalized_slot)
-//            if ancestor_at_finalized_slot != store.finalized_checkpoint.root:
-//                store.justified_checkpoint = state.current_justified_checkpoint
-func (s *Service) finalizedImpliesNewJustified(ctx context.Context, state state.BeaconState) error {
-	// Update justified if it's different than the one cached in the store.
-	if !attestation.CheckPointIsEqual(s.justifiedCheckpt, state.CurrentJustifiedCheckpoint()) {
-		if state.CurrentJustifiedCheckpoint().Epoch > s.justifiedCheckpt.Epoch {
-			s.justifiedCheckpt = state.CurrentJustifiedCheckpoint()
-			return s.cacheJustifiedStateBalances(ctx, bytesutil.ToBytes32(s.justifiedCheckpt.Root))
-		}
-
-		// Update justified if store justified is not in chain with finalized check point.
-		finalizedSlot, err := core.StartSlot(s.finalizedCheckpt.Epoch)
-		if err != nil {
-			return err
-		}
-		justifiedRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(s.justifiedCheckpt.Root))
-		anc, err := s.ancestor(ctx, justifiedRoot[:], finalizedSlot)
-		if err != nil {
-			return err
-		}
-		if !bytes.Equal(anc, s.finalizedCheckpt.Root) {
-			s.justifiedCheckpt = state.CurrentJustifiedCheckpoint()
-			if err := s.cacheJustifiedStateBalances(ctx, bytesutil.ToBytes32(s.justifiedCheckpt.Root)); err != nil {
-				return err
-			}
-		}
-	}
-	return nil
-}
-
 // This retrieves missing blocks from DB (ie. the blocks that couldn't be received over sync) and inserts them to fork choice store.
 // This is useful for block tree visualizer and additional vote accounting.
 func (s *Service) fillInForkChoiceMissingBlocks(ctx context.Context, blk block.BeaconBlock,
@@ -382,7 +337,11 @@ func (s *Service) fillInForkChoiceMissingBlocks(ctx context.Context, blk block.B
 	parentRoot := bytesutil.ToBytes32(blk.ParentRoot())
 	slot := blk.Slot()
 	// Fork choice only matters from last finalized slot.
-	fSlot, err := core.StartSlot(s.finalizedCheckpt.Epoch)
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	fSlot, err := slots.EpochStart(finalized.Epoch)
 	if err != nil {
 		return err
 	}
@@ -408,9 +367,9 @@ func (s *Service) fillInForkChoiceMissingBlocks(ctx context.Context, blk block.B
 		b := pendingNodes[i]
 		r := pendingRoots[i]
 		if err := s.cfg.ForkChoiceStore.ProcessBlock(ctx,
-			b.Slot(), r, bytesutil.ToBytes32(b.ParentRoot()), bytesutil.ToBytes32(b.Body().Graffiti()),
+			b.Slot(), r, bytesutil.ToBytes32(b.ParentRoot()),
 			jCheckpoint.Epoch,
-			fCheckpoint.Epoch); err != nil {
+			fCheckpoint.Epoch, false /* optimistic status */); err != nil {
 			return errors.Wrap(err, "could not process block for proto array fork choice")
 		}
 	}
@@ -461,7 +420,7 @@ func (s *Service) deletePoolAtts(atts []*ethpb.Attestation) error {
 // fork choice justification routine.
 func (s *Service) ensureRootNotZeros(root [32]byte) [32]byte {
 	if root == params.BeaconConfig().ZeroHash {
-		return s.genesisRoot
+		return s.originBlockRoot
 	}
 	return root
 }
--- a/beacon-chain/blockchain/process_block_test.go
+++ b/beacon-chain/blockchain/process_block_test.go
--- a/beacon-chain/blockchain/receive_attestation.go
+++ b/beacon-chain/blockchain/receive_attestation.go
@@ -7,22 +7,28 @@ import (
 	"time"

 	"github.com/pkg/errors"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
+	"github.com/prysmaticlabs/prysm/async/event"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/feed"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
 	"github.com/prysmaticlabs/prysm/time/slots"
 	"github.com/sirupsen/logrus"
 	"go.opencensus.io/trace"
 )

+// AttestationStateFetcher allows for retrieving a beacon state corresponding to the block
+// root of an attestation's target checkpoint.
+type AttestationStateFetcher interface {
+	AttestationTargetState(ctx context.Context, target *ethpb.Checkpoint) (state.BeaconState, error)
+}
+
 // AttestationReceiver interface defines the methods of chain service receive and processing new attestations.
 type AttestationReceiver interface {
+	AttestationStateFetcher
 	ReceiveAttestationNoPubsub(ctx context.Context, att *ethpb.Attestation) error
-	AttestationPreState(ctx context.Context, att *ethpb.Attestation) (state.BeaconState, error)
 	VerifyLmdFfgConsistency(ctx context.Context, att *ethpb.Attestation) error
 	VerifyFinalizedConsistency(ctx context.Context, root []byte) error
 }
@@ -36,28 +42,28 @@ func (s *Service) ReceiveAttestationNoPubsub(ctx context.Context, att *ethpb.Att
 	ctx, span := trace.StartSpan(ctx, "beacon-chain.blockchain.ReceiveAttestationNoPubsub")
 	defer span.End()

-	if err := s.onAttestation(ctx, att); err != nil {
+	if err := s.OnAttestation(ctx, att); err != nil {
 		return errors.Wrap(err, "could not process attestation")
 	}

 	return nil
 }

-// AttestationPreState returns the pre state of attestation.
-func (s *Service) AttestationPreState(ctx context.Context, att *ethpb.Attestation) (state.BeaconState, error) {
-	ss, err := core.StartSlot(att.Data.Target.Epoch)
+// AttestationTargetState returns the pre state of attestation.
+func (s *Service) AttestationTargetState(ctx context.Context, target *ethpb.Checkpoint) (state.BeaconState, error) {
+	ss, err := slots.EpochStart(target.Epoch)
 	if err != nil {
 		return nil, err
 	}
-	if err := core.ValidateSlotClock(ss, uint64(s.genesisTime.Unix())); err != nil {
+	if err := slots.ValidateClock(ss, uint64(s.genesisTime.Unix())); err != nil {
 		return nil, err
 	}
-	return s.getAttPreState(ctx, att.Data.Target)
+	return s.getAttPreState(ctx, target)
 }

 // VerifyLmdFfgConsistency verifies that attestation's LMD and FFG votes are consistency to each other.
 func (s *Service) VerifyLmdFfgConsistency(ctx context.Context, a *ethpb.Attestation) error {
-	targetSlot, err := core.StartSlot(a.Data.Target.Epoch)
+	targetSlot, err := slots.EpochStart(a.Data.Target.Epoch)
 	if err != nil {
 		return err
 	}
@@ -82,7 +88,10 @@ func (s *Service) VerifyFinalizedConsistency(ctx context.Context, root []byte) e
 	}

 	f := s.FinalizedCheckpt()
-	ss, err := core.StartSlot(f.Epoch)
+	if f == nil {
+		return errNilFinalizedInStore
+	}
+	ss, err := slots.EpochStart(f.Epoch)
 	if err != nil {
 		return err
 	}
@@ -98,39 +107,66 @@ func (s *Service) VerifyFinalizedConsistency(ctx context.Context, root []byte) e
 }

 // This routine processes fork choice attestations from the pool to account for validator votes and fork choice.
-func (s *Service) processAttestationsRoutine(subscribedToStateEvents chan<- struct{}) {
+func (s *Service) spawnProcessAttestationsRoutine(stateFeed *event.Feed) {
 	// Wait for state to be initialized.
 	stateChannel := make(chan *feed.Event, 1)
-	stateSub := s.cfg.StateNotifier.StateFeed().Subscribe(stateChannel)
-	subscribedToStateEvents <- struct{}{}
-	<-stateChannel
-	stateSub.Unsubscribe()
-
-	if s.genesisTime.IsZero() {
-		log.Warn("ProcessAttestations routine waiting for genesis time")
-		for s.genesisTime.IsZero() {
-			time.Sleep(1 * time.Second)
-		}
-		log.Warn("Genesis time received, now available to process attestations")
-	}
-
-	st := slots.NewSlotTicker(s.genesisTime, params.BeaconConfig().SecondsPerSlot)
-	for {
+	stateSub := stateFeed.Subscribe(stateChannel)
+	go func() {
 		select {
 		case <-s.ctx.Done():
+			stateSub.Unsubscribe()
 			return
-		case <-st.C():
-			// Continue when there's no fork choice attestation, there's nothing to process and update head.
-			// This covers the condition when the node is still initial syncing to the head of the chain.
-			if s.cfg.AttPool.ForkchoiceAttestationCount() == 0 {
-				continue
+		case <-stateChannel:
+			stateSub.Unsubscribe()
+			break
+		}
+
+		if s.genesisTime.IsZero() {
+			log.Warn("ProcessAttestations routine waiting for genesis time")
+			for s.genesisTime.IsZero() {
+				if err := s.ctx.Err(); err != nil {
+					log.WithError(err).Error("Giving up waiting for genesis time")
+					return
+				}
+				time.Sleep(1 * time.Second)
 			}
-			s.processAttestations(s.ctx)
-			if err := s.updateHead(s.ctx, s.getJustifiedBalances()); err != nil {
-				log.Warnf("Resolving fork due to new attestation: %v", err)
+			log.Warn("Genesis time received, now available to process attestations")
+		}
+
+		st := slots.NewSlotTicker(s.genesisTime, params.BeaconConfig().SecondsPerSlot)
+		for {
+			select {
+			case <-s.ctx.Done():
+				return
+			case <-st.C():
+				if err := s.NewSlot(s.ctx, s.CurrentSlot()); err != nil {
+					log.WithError(err).Error("Could not process new slot")
+					return
+				}
+
+				// Continue when there's no fork choice attestation, there's nothing to process and update head.
+				// This covers the condition when the node is still initial syncing to the head of the chain.
+				if s.cfg.AttPool.ForkchoiceAttestationCount() == 0 {
+					continue
+				}
+				s.processAttestations(s.ctx)
+
+				justified := s.store.JustifiedCheckpt()
+				if justified == nil {
+					log.WithError(errNilJustifiedInStore).Error("Could not get justified checkpoint")
+					continue
+				}
+				balances, err := s.justifiedBalances.get(s.ctx, bytesutil.ToBytes32(justified.Root))
+				if err != nil {
+					log.WithError(err).Errorf("Unable to get justified balances for root %v", justified.Root)
+					continue
+				}
+				if err := s.updateHead(s.ctx, balances); err != nil {
+					log.WithError(err).Warn("Resolving fork due to new attestation")
+				}
 			}
 		}
-	}
+	}()
 }

 // This processes fork choice attestations from the pool to account for validator votes and fork choice.
@@ -141,7 +177,7 @@ func (s *Service) processAttestations(ctx context.Context) {
 		// This delays consideration in the fork choice until their slot is in the past.
 		// https://github.com/ethereum/consensus-specs/blob/dev/specs/phase0/fork-choice.md#validate_on_attestation
 		nextSlot := a.Data.Slot + 1
-		if err := core.VerifySlotTime(uint64(s.genesisTime.Unix()), nextSlot, params.BeaconNetworkConfig().MaximumGossipClockDisparity); err != nil {
+		if err := slots.VerifyTime(uint64(s.genesisTime.Unix()), nextSlot, params.BeaconNetworkConfig().MaximumGossipClockDisparity); err != nil {
 			continue
 		}

--- a/beacon-chain/blockchain/receive_attestation_test.go
+++ b/beacon-chain/blockchain/receive_attestation_test.go
@@ -6,23 +6,26 @@ import (
 	"time"

 	types "github.com/prysmaticlabs/eth2-types"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
-	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/attestations"
-	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
 	prysmTime "github.com/prysmaticlabs/prysm/time"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 )

+var (
+	_ = AttestationReceiver(&Service{})
+	_ = AttestationStateFetcher(&Service{})
+)
+
 func TestAttestationCheckPtState_FarFutureSlot(t *testing.T) {
 	helpers.ClearCache()
 	beaconDB := testDB.SetupDB(t)
@@ -30,25 +33,24 @@ func TestAttestationCheckPtState_FarFutureSlot(t *testing.T) {
 	chainService := setupBeaconChain(t, beaconDB)
 	chainService.genesisTime = time.Now()

-	e := types.Epoch(core.MaxSlotBuffer/uint64(params.BeaconConfig().SlotsPerEpoch) + 1)
-	_, err := chainService.AttestationPreState(context.Background(), &ethpb.Attestation{Data: &ethpb.AttestationData{Target: &ethpb.Checkpoint{Epoch: e}}})
+	e := types.Epoch(slots.MaxSlotBuffer/uint64(params.BeaconConfig().SlotsPerEpoch) + 1)
+	_, err := chainService.AttestationTargetState(context.Background(), &ethpb.Checkpoint{Epoch: e})
 	require.ErrorContains(t, "exceeds max allowed value relative to the local clock", err)
 }

 func TestVerifyLMDFFGConsistent_NotOK(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
+	opts := testServiceOptsWithDB(t)

-	cfg := &Config{BeaconDB: beaconDB, ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}
-	service, err := NewService(ctx, cfg)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b32 := testutil.NewBeaconBlock()
+	b32 := util.NewBeaconBlock()
 	b32.Block.Slot = 32
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b32)))
 	r32, err := b32.Block.HashTreeRoot()
 	require.NoError(t, err)
-	b33 := testutil.NewBeaconBlock()
+	b33 := util.NewBeaconBlock()
 	b33.Block.Slot = 33
 	b33.Block.ParentRoot = r32[:]
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b33)))
@@ -56,7 +58,7 @@ func TestVerifyLMDFFGConsistent_NotOK(t *testing.T) {
 	require.NoError(t, err)

 	wanted := "FFG and LMD votes are not consistent"
-	a := testutil.NewAttestation()
+	a := util.NewAttestation()
 	a.Data.Target.Epoch = 1
 	a.Data.Target.Root = []byte{'a'}
 	a.Data.BeaconBlockRoot = r33[:]
@@ -65,25 +67,24 @@ func TestVerifyLMDFFGConsistent_NotOK(t *testing.T) {

 func TestVerifyLMDFFGConsistent_OK(t *testing.T) {
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)

-	cfg := &Config{BeaconDB: beaconDB, ForkChoiceStore: protoarray.New(0, 0, [32]byte{})}
-	service, err := NewService(ctx, cfg)
+	opts := testServiceOptsWithDB(t)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)

-	b32 := testutil.NewBeaconBlock()
+	b32 := util.NewBeaconBlock()
 	b32.Block.Slot = 32
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b32)))
 	r32, err := b32.Block.HashTreeRoot()
 	require.NoError(t, err)
-	b33 := testutil.NewBeaconBlock()
+	b33 := util.NewBeaconBlock()
 	b33.Block.Slot = 33
 	b33.Block.ParentRoot = r32[:]
 	require.NoError(t, service.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(b33)))
 	r33, err := b33.Block.HashTreeRoot()
 	require.NoError(t, err)

-	a := testutil.NewAttestation()
+	a := util.NewAttestation()
 	a.Data.Target.Epoch = 1
 	a.Data.Target.Root = r32[:]
 	a.Data.BeaconBlockRoot = r33[:]
@@ -94,28 +95,23 @@ func TestVerifyLMDFFGConsistent_OK(t *testing.T) {
 func TestProcessAttestations_Ok(t *testing.T) {
 	hook := logTest.NewGlobal()
 	ctx := context.Background()
-	beaconDB := testDB.SetupDB(t)
+	opts := testServiceOptsWithDB(t)
+	opts = append(opts, WithAttestationPool(attestations.NewPool()))

-	cfg := &Config{
-		BeaconDB:        beaconDB,
-		ForkChoiceStore: protoarray.New(0, 0, [32]byte{}),
-		StateGen:        stategen.New(beaconDB),
-		AttPool:         attestations.NewPool(),
-	}
-	service, err := NewService(ctx, cfg)
-	service.genesisTime = prysmTime.Now().Add(-1 * time.Duration(params.BeaconConfig().SecondsPerSlot) * time.Second)
+	service, err := NewService(ctx, opts...)
 	require.NoError(t, err)
-	genesisState, pks := testutil.DeterministicGenesisState(t, 64)
+	service.genesisTime = prysmTime.Now().Add(-1 * time.Duration(params.BeaconConfig().SecondsPerSlot) * time.Second)
+	genesisState, pks := util.DeterministicGenesisState(t, 64)
 	require.NoError(t, genesisState.SetGenesisTime(uint64(prysmTime.Now().Unix())-params.BeaconConfig().SecondsPerSlot))
 	require.NoError(t, service.saveGenesisData(ctx, genesisState))
-	atts, err := testutil.GenerateAttestations(genesisState, pks, 1, 0, false)
+	atts, err := util.GenerateAttestations(genesisState, pks, 1, 0, false)
 	require.NoError(t, err)
 	tRoot := bytesutil.ToBytes32(atts[0].Data.Target.Root)
 	copied := genesisState.Copy()
 	copied, err = transition.ProcessSlots(ctx, copied, 1)
 	require.NoError(t, err)
 	require.NoError(t, service.cfg.BeaconDB.SaveState(ctx, copied, tRoot))
-	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, 0, tRoot, tRoot, tRoot, 1, 1))
+	require.NoError(t, service.cfg.ForkChoiceStore.ProcessBlock(ctx, 0, tRoot, tRoot, 1, 1, false))
 	require.NoError(t, service.cfg.AttPool.SaveForkchoiceAttestations(atts))
 	service.processAttestations(ctx)
 	require.Equal(t, 0, len(service.cfg.AttPool.ForkchoiceAttestations()))
--- a/beacon-chain/blockchain/receive_block.go
+++ b/beacon-chain/blockchain/receive_block.go
@@ -5,13 +5,12 @@ import (

 	"github.com/pkg/errors"
 	types "github.com/prysmaticlabs/eth2-types"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/feed"
 	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
-	"github.com/prysmaticlabs/prysm/config/features"
 	"github.com/prysmaticlabs/prysm/monitoring/tracing"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
 	"github.com/prysmaticlabs/prysm/time"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	"go.opencensus.io/trace"
 )

@@ -43,28 +42,6 @@ func (s *Service) ReceiveBlock(ctx context.Context, block block.SignedBeaconBloc
 		return err
 	}

-	// Update and save head block after fork choice.
-	if !features.Get().UpdateHeadTimely {
-		if err := s.updateHead(ctx, s.getJustifiedBalances()); err != nil {
-			log.WithError(err).Warn("Could not update head")
-		}
-
-		if err := s.pruneCanonicalAttsFromPool(ctx, blockRoot, block); err != nil {
-			return err
-		}
-
-		// Send notification of the processed block to the state feed.
-		s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
-			Type: statefeed.BlockProcessed,
-			Data: &statefeed.BlockProcessedData{
-				Slot:        blockCopy.Block().Slot(),
-				BlockRoot:   blockRoot,
-				SignedBlock: blockCopy,
-				Verified:    true,
-			},
-		})
-	}
-
 	// Handle post block operations such as attestations and exits.
 	if err := s.handlePostBlockOperations(blockCopy.Block()); err != nil {
 		return err
@@ -76,10 +53,14 @@ func (s *Service) ReceiveBlock(ctx context.Context, block block.SignedBeaconBloc
 	}

 	// Reports on block and fork choice metrics.
-	reportSlotMetrics(blockCopy.Block().Slot(), s.HeadSlot(), s.CurrentSlot(), s.finalizedCheckpt)
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	reportSlotMetrics(blockCopy.Block().Slot(), s.HeadSlot(), s.CurrentSlot(), finalized)

 	// Log block sync status.
-	if err := logBlockSyncStatus(blockCopy.Block(), blockRoot, s.finalizedCheckpt, receivedTime, uint64(s.genesisTime.Unix())); err != nil {
+	if err := logBlockSyncStatus(blockCopy.Block(), blockRoot, finalized, receivedTime, uint64(s.genesisTime.Unix())); err != nil {
 		return err
 	}
 	// Log state transition data.
@@ -96,7 +77,7 @@ func (s *Service) ReceiveBlockBatch(ctx context.Context, blocks []block.SignedBe
 	defer span.End()

 	// Apply state transition on the incoming newly received blockCopy without verifying its BLS contents.
-	fCheckpoints, jCheckpoints, err := s.onBlockBatch(ctx, blocks, blkRoots)
+	fCheckpoints, jCheckpoints, optimistic, err := s.onBlockBatch(ctx, blocks, blkRoots)
 	if err != nil {
 		err := errors.Wrap(err, "could not process block in batch")
 		tracing.AnnotateError(span, err)
@@ -105,10 +86,21 @@ func (s *Service) ReceiveBlockBatch(ctx context.Context, blocks []block.SignedBe

 	for i, b := range blocks {
 		blockCopy := b.Copy()
-		if err = s.handleBlockAfterBatchVerify(ctx, blockCopy, blkRoots[i], fCheckpoints[i], jCheckpoints[i]); err != nil {
+		// TODO(10261) check optimistic status
+		if err = s.handleBlockAfterBatchVerify(ctx, blockCopy, blkRoots[i], fCheckpoints[i], jCheckpoints[i], false /*optimistic status*/); err != nil {
 			tracing.AnnotateError(span, err)
 			return err
 		}
+		if !optimistic[i] {
+			root, err := b.Block().HashTreeRoot()
+			if err != nil {
+				return err
+			}
+			if err := s.cfg.ForkChoiceStore.SetOptimisticToValid(ctx, root); err != nil {
+				return err
+			}
+		}
+
 		// Send notification of the processed block to the state feed.
 		s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
 			Type: statefeed.BlockProcessed,
@@ -121,10 +113,21 @@ func (s *Service) ReceiveBlockBatch(ctx context.Context, blocks []block.SignedBe
 		})

 		// Reports on blockCopy and fork choice metrics.
-		reportSlotMetrics(blockCopy.Block().Slot(), s.HeadSlot(), s.CurrentSlot(), s.finalizedCheckpt)
+		finalized := s.store.FinalizedCheckpt()
+		if finalized == nil {
+			return errNilFinalizedInStore
+		}
+		reportSlotMetrics(blockCopy.Block().Slot(), s.HeadSlot(), s.CurrentSlot(), finalized)
 	}

-	if err := s.VerifyWeakSubjectivityRoot(s.ctx); err != nil {
+	if err := s.cfg.BeaconDB.SaveBlocks(ctx, s.getInitSyncBlocks()); err != nil {
+		return err
+	}
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	if err := s.wsVerifier.VerifyWeakSubjectivity(s.ctx, finalized.Epoch); err != nil {
 		// log.Fatalf will prevent defer from being called
 		span.End()
 		// Exit run time if the node failed to verify weak subjectivity checkpoint.
@@ -165,11 +168,15 @@ func (s *Service) handlePostBlockOperations(b block.BeaconBlock) error {
 // This checks whether it's time to start saving hot state to DB.
 // It's time when there's `epochsSinceFinalitySaveHotStateDB` epochs of non-finality.
 func (s *Service) checkSaveHotStateDB(ctx context.Context) error {
-	currentEpoch := core.SlotToEpoch(s.CurrentSlot())
+	currentEpoch := slots.ToEpoch(s.CurrentSlot())
 	// Prevent `sinceFinality` going underflow.
 	var sinceFinality types.Epoch
-	if currentEpoch > s.finalizedCheckpt.Epoch {
-		sinceFinality = currentEpoch - s.finalizedCheckpt.Epoch
+	finalized := s.store.FinalizedCheckpt()
+	if finalized == nil {
+		return errNilFinalizedInStore
+	}
+	if currentEpoch > finalized.Epoch {
+		sinceFinality = currentEpoch - finalized.Epoch
 	}

 	if sinceFinality >= epochsSinceFinalitySaveHotStateDB {
--- a/beacon-chain/blockchain/receive_block_test.go
+++ b/beacon-chain/blockchain/receive_block_test.go
@@ -8,33 +8,32 @@ import (

 	types "github.com/prysmaticlabs/eth2-types"
 	blockchainTesting "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/attestations"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/voluntaryexits"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
-	"github.com/prysmaticlabs/prysm/config/features"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 )

 func TestService_ReceiveBlock(t *testing.T) {
 	ctx := context.Background()

-	genesis, keys := testutil.DeterministicGenesisState(t, 64)
-	genFullBlock := func(t *testing.T, conf *testutil.BlockGenConfig, slot types.Slot) *ethpb.SignedBeaconBlock {
-		blk, err := testutil.GenerateFullBlock(genesis, keys, conf, slot)
+	genesis, keys := util.DeterministicGenesisState(t, 64)
+	genFullBlock := func(t *testing.T, conf *util.BlockGenConfig, slot types.Slot) *ethpb.SignedBeaconBlock {
+		blk, err := util.GenerateFullBlock(genesis, keys, conf, slot)
 		assert.NoError(t, err)
 		return blk
 	}
+	params.SetupTestConfigCleanup(t)
 	bc := params.BeaconConfig()
 	bc.ShardCommitteePeriod = 0 // Required for voluntary exits test in reasonable time.
 	params.OverrideBeaconConfig(bc)
@@ -51,7 +50,7 @@ func TestService_ReceiveBlock(t *testing.T) {
 		{
 			name: "applies block with state transition",
 			args: args{
-				block: genFullBlock(t, testutil.DefaultBlockGenConfig(), 2 /*slot*/),
+				block: genFullBlock(t, util.DefaultBlockGenConfig(), 2 /*slot*/),
 			},
 			check: func(t *testing.T, s *Service) {
 				if hs := s.head.state.Slot(); hs != 2 {
@@ -66,7 +65,7 @@ func TestService_ReceiveBlock(t *testing.T) {
 			name: "saves attestations to pool",
 			args: args{
 				block: genFullBlock(t,
-					&testutil.BlockGenConfig{
+					&util.BlockGenConfig{
 						NumProposerSlashings: 0,
 						NumAttesterSlashings: 0,
 						NumAttestations:      2,
@@ -86,7 +85,7 @@ func TestService_ReceiveBlock(t *testing.T) {
 		{
 			name: "updates exit pool",
 			args: args{
-				block: genFullBlock(t, &testutil.BlockGenConfig{
+				block: genFullBlock(t, &util.BlockGenConfig{
 					NumProposerSlashings: 0,
 					NumAttesterSlashings: 0,
 					NumAttestations:      0,
@@ -110,7 +109,7 @@ func TestService_ReceiveBlock(t *testing.T) {
 		{
 			name: "notifies block processed on state feed",
 			args: args{
-				block: genFullBlock(t, testutil.DefaultBlockGenConfig(), 1 /*slot*/),
+				block: genFullBlock(t, util.DefaultBlockGenConfig(), 1 /*slot*/),
 			},
 			check: func(t *testing.T, s *Service) {
 				if recvd := len(s.cfg.StateNotifier.(*blockchainTesting.MockStateNotifier).ReceivedEvents()); recvd < 1 {
@@ -126,26 +125,22 @@ func TestService_ReceiveBlock(t *testing.T) {
 			genesisBlockRoot := bytesutil.ToBytes32(nil)
 			require.NoError(t, beaconDB.SaveState(ctx, genesis, genesisBlockRoot))

-			cfg := &Config{
-				BeaconDB: beaconDB,
-				ForkChoiceStore: protoarray.New(
-					0, // justifiedEpoch
-					0, // finalizedEpoch
-					genesisBlockRoot,
-				),
-				AttPool:       attestations.NewPool(),
-				ExitPool:      voluntaryexits.NewPool(),
-				StateNotifier: &blockchainTesting.MockStateNotifier{RecordEvents: true},
-				StateGen:      stategen.New(beaconDB),
+			opts := []Option{
+				WithDatabase(beaconDB),
+				WithForkChoiceStore(protoarray.New(0, 0, genesisBlockRoot)),
+				WithAttestationPool(attestations.NewPool()),
+				WithExitPool(voluntaryexits.NewPool()),
+				WithStateNotifier(&blockchainTesting.MockStateNotifier{RecordEvents: true}),
+				WithStateGen(stategen.New(beaconDB)),
 			}
-			s, err := NewService(ctx, cfg)
+			s, err := NewService(ctx, opts...)
 			require.NoError(t, err)
 			require.NoError(t, s.saveGenesisData(ctx, genesis))
 			gBlk, err := s.cfg.BeaconDB.GenesisBlock(ctx)
 			require.NoError(t, err)
 			gRoot, err := gBlk.Block().HashTreeRoot()
 			require.NoError(t, err)
-			s.finalizedCheckpt = &ethpb.Checkpoint{Root: gRoot[:]}
+			s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: gRoot[:]})
 			root, err := tt.args.block.Block.HashTreeRoot()
 			require.NoError(t, err)
 			err = s.ReceiveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(tt.args.block), root)
@@ -161,32 +156,29 @@ func TestService_ReceiveBlock(t *testing.T) {

 func TestService_ReceiveBlockUpdateHead(t *testing.T) {
 	ctx := context.Background()
-	genesis, keys := testutil.DeterministicGenesisState(t, 64)
-	b, err := testutil.GenerateFullBlock(genesis, keys, testutil.DefaultBlockGenConfig(), 1)
+	genesis, keys := util.DeterministicGenesisState(t, 64)
+	b, err := util.GenerateFullBlock(genesis, keys, util.DefaultBlockGenConfig(), 1)
 	assert.NoError(t, err)
 	beaconDB := testDB.SetupDB(t)
 	genesisBlockRoot := bytesutil.ToBytes32(nil)
 	require.NoError(t, beaconDB.SaveState(ctx, genesis, genesisBlockRoot))
-	cfg := &Config{
-		BeaconDB: beaconDB,
-		ForkChoiceStore: protoarray.New(
-			0, // justifiedEpoch
-			0, // finalizedEpoch
-			genesisBlockRoot,
-		),
-		AttPool:       attestations.NewPool(),
-		ExitPool:      voluntaryexits.NewPool(),
-		StateNotifier: &blockchainTesting.MockStateNotifier{RecordEvents: true},
-		StateGen:      stategen.New(beaconDB),
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithForkChoiceStore(protoarray.New(0, 0, genesisBlockRoot)),
+		WithAttestationPool(attestations.NewPool()),
+		WithExitPool(voluntaryexits.NewPool()),
+		WithStateNotifier(&blockchainTesting.MockStateNotifier{RecordEvents: true}),
+		WithStateGen(stategen.New(beaconDB)),
 	}
-	s, err := NewService(ctx, cfg)
+
+	s, err := NewService(ctx, opts...)
 	require.NoError(t, err)
 	require.NoError(t, s.saveGenesisData(ctx, genesis))
 	gBlk, err := s.cfg.BeaconDB.GenesisBlock(ctx)
 	require.NoError(t, err)
 	gRoot, err := gBlk.Block().HashTreeRoot()
 	require.NoError(t, err)
-	s.finalizedCheckpt = &ethpb.Checkpoint{Root: gRoot[:]}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: gRoot[:]})
 	root, err := b.Block.HashTreeRoot()
 	require.NoError(t, err)
 	wg := sync.WaitGroup{}
@@ -200,15 +192,15 @@ func TestService_ReceiveBlockUpdateHead(t *testing.T) {
 		t.Errorf("Received %d state notifications, expected at least 1", recvd)
 	}
 	// Verify fork choice has processed the block. (Genesis block and the new block)
-	assert.Equal(t, 2, len(s.cfg.ForkChoiceStore.Nodes()))
+	assert.Equal(t, 2, s.cfg.ForkChoiceStore.NodeCount())
 }

 func TestService_ReceiveBlockBatch(t *testing.T) {
 	ctx := context.Background()

-	genesis, keys := testutil.DeterministicGenesisState(t, 64)
-	genFullBlock := func(t *testing.T, conf *testutil.BlockGenConfig, slot types.Slot) *ethpb.SignedBeaconBlock {
-		blk, err := testutil.GenerateFullBlock(genesis, keys, conf, slot)
+	genesis, keys := util.DeterministicGenesisState(t, 64)
+	genFullBlock := func(t *testing.T, conf *util.BlockGenConfig, slot types.Slot) *ethpb.SignedBeaconBlock {
+		blk, err := util.GenerateFullBlock(genesis, keys, conf, slot)
 		assert.NoError(t, err)
 		return blk
 	}
@@ -225,7 +217,7 @@ func TestService_ReceiveBlockBatch(t *testing.T) {
 		{
 			name: "applies block with state transition",
 			args: args{
-				block: genFullBlock(t, testutil.DefaultBlockGenConfig(), 2 /*slot*/),
+				block: genFullBlock(t, util.DefaultBlockGenConfig(), 2 /*slot*/),
 			},
 			check: func(t *testing.T, s *Service) {
 				assert.Equal(t, types.Slot(2), s.head.state.Slot(), "Incorrect head state slot")
@@ -235,7 +227,7 @@ func TestService_ReceiveBlockBatch(t *testing.T) {
 		{
 			name: "notifies block processed on state feed",
 			args: args{
-				block: genFullBlock(t, testutil.DefaultBlockGenConfig(), 1 /*slot*/),
+				block: genFullBlock(t, util.DefaultBlockGenConfig(), 1 /*slot*/),
 			},
 			check: func(t *testing.T, s *Service) {
 				if recvd := len(s.cfg.StateNotifier.(*blockchainTesting.MockStateNotifier).ReceivedEvents()); recvd < 1 {
@@ -250,17 +242,13 @@ func TestService_ReceiveBlockBatch(t *testing.T) {
 			beaconDB := testDB.SetupDB(t)
 			genesisBlockRoot, err := genesis.HashTreeRoot(ctx)
 			require.NoError(t, err)
-			cfg := &Config{
-				BeaconDB: beaconDB,
-				ForkChoiceStore: protoarray.New(
-					0, // justifiedEpoch
-					0, // finalizedEpoch
-					genesisBlockRoot,
-				),
-				StateNotifier: &blockchainTesting.MockStateNotifier{RecordEvents: true},
-				StateGen:      stategen.New(beaconDB),
+			opts := []Option{
+				WithDatabase(beaconDB),
+				WithForkChoiceStore(protoarray.New(0, 0, genesisBlockRoot)),
+				WithStateNotifier(&blockchainTesting.MockStateNotifier{RecordEvents: true}),
+				WithStateGen(stategen.New(beaconDB)),
 			}
-			s, err := NewService(ctx, cfg)
+			s, err := NewService(ctx, opts...)
 			require.NoError(t, err)
 			err = s.saveGenesisData(ctx, genesis)
 			require.NoError(t, err)
@@ -269,7 +257,7 @@ func TestService_ReceiveBlockBatch(t *testing.T) {

 			gRoot, err := gBlk.Block().HashTreeRoot()
 			require.NoError(t, err)
-			s.finalizedCheckpt = &ethpb.Checkpoint{Root: gRoot[:]}
+			s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Root: gRoot[:]})
 			root, err := tt.args.block.Block.HashTreeRoot()
 			require.NoError(t, err)
 			blks := []block.SignedBeaconBlock{wrapper.WrappedPhase0SignedBeaconBlock(tt.args.block)}
@@ -285,94 +273,40 @@ func TestService_ReceiveBlockBatch(t *testing.T) {
 	}
 }

-func TestService_ReceiveBlockBatch_UpdateFinalizedCheckpoint(t *testing.T) {
-	// Must enable head timely feature flag to test this.
-	resetCfg := features.InitWithReset(&features.Flags{
-		UpdateHeadTimely: true,
-	})
-	defer resetCfg()
-
-	ctx := context.Background()
-	genesis, keys := testutil.DeterministicGenesisState(t, 64)
-
-	// Generate 5 epochs worth of blocks.
-	var blks []block.SignedBeaconBlock
-	var roots [][32]byte
-	copied := genesis.Copy()
-	for i := types.Slot(1); i < params.BeaconConfig().SlotsPerEpoch*5; i++ {
-		b, err := testutil.GenerateFullBlock(copied, keys, testutil.DefaultBlockGenConfig(), i)
-		assert.NoError(t, err)
-		copied, err = transition.ExecuteStateTransition(context.Background(), copied, wrapper.WrappedPhase0SignedBeaconBlock(b))
-		assert.NoError(t, err)
-		r, err := b.Block.HashTreeRoot()
-		require.NoError(t, err)
-		blks = append(blks, wrapper.WrappedPhase0SignedBeaconBlock(b))
-		roots = append(roots, r)
-	}
-
-	beaconDB := testDB.SetupDB(t)
-	genesisBlockRoot, err := genesis.HashTreeRoot(ctx)
-	require.NoError(t, err)
-	cfg := &Config{
-		BeaconDB: beaconDB,
-		ForkChoiceStore: protoarray.New(
-			0, // justifiedEpoch
-			0, // finalizedEpoch
-			genesisBlockRoot,
-		),
-		StateNotifier: &blockchainTesting.MockStateNotifier{RecordEvents: false},
-		StateGen:      stategen.New(beaconDB),
-	}
-	s, err := NewService(ctx, cfg)
-	require.NoError(t, err)
-	err = s.saveGenesisData(ctx, genesis)
-	require.NoError(t, err)
-	gBlk, err := s.cfg.BeaconDB.GenesisBlock(ctx)
-	require.NoError(t, err)
-
-	gRoot, err := gBlk.Block().HashTreeRoot()
-	require.NoError(t, err)
-	s.finalizedCheckpt = &ethpb.Checkpoint{Root: gRoot[:]}
-
-	// Process 5 epochs worth of blocks.
-	require.NoError(t, s.ReceiveBlockBatch(ctx, blks, roots))
-
-	// Finalized epoch must be updated.
-	require.Equal(t, types.Epoch(2), s.finalizedCheckpt.Epoch)
-}
-
 func TestService_HasInitSyncBlock(t *testing.T) {
-	s, err := NewService(context.Background(), &Config{StateNotifier: &blockchainTesting.MockStateNotifier{}})
+	opts := testServiceOptsNoDB()
+	opts = append(opts, WithStateNotifier(&blockchainTesting.MockStateNotifier{}))
+	s, err := NewService(context.Background(), opts...)
 	require.NoError(t, err)
 	r := [32]byte{'a'}
 	if s.HasInitSyncBlock(r) {
 		t.Error("Should not have block")
 	}
-	s.saveInitSyncBlock(r, wrapper.WrappedPhase0SignedBeaconBlock(testutil.NewBeaconBlock()))
+	s.saveInitSyncBlock(r, wrapper.WrappedPhase0SignedBeaconBlock(util.NewBeaconBlock()))
 	if !s.HasInitSyncBlock(r) {
 		t.Error("Should have block")
 	}
 }

 func TestCheckSaveHotStateDB_Enabling(t *testing.T) {
-	beaconDB := testDB.SetupDB(t)
+	opts := testServiceOptsWithDB(t)
 	hook := logTest.NewGlobal()
-	s, err := NewService(context.Background(), &Config{StateGen: stategen.New(beaconDB)})
+	s, err := NewService(context.Background(), opts...)
 	require.NoError(t, err)
 	st := params.BeaconConfig().SlotsPerEpoch.Mul(uint64(epochsSinceFinalitySaveHotStateDB))
 	s.genesisTime = time.Now().Add(time.Duration(-1*int64(st)*int64(params.BeaconConfig().SecondsPerSlot)) * time.Second)
-	s.finalizedCheckpt = &ethpb.Checkpoint{}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{})

 	require.NoError(t, s.checkSaveHotStateDB(context.Background()))
 	assert.LogsContain(t, hook, "Entering mode to save hot states in DB")
 }

 func TestCheckSaveHotStateDB_Disabling(t *testing.T) {
-	beaconDB := testDB.SetupDB(t)
 	hook := logTest.NewGlobal()
-	s, err := NewService(context.Background(), &Config{StateGen: stategen.New(beaconDB)})
+	opts := testServiceOptsWithDB(t)
+	s, err := NewService(context.Background(), opts...)
 	require.NoError(t, err)
-	s.finalizedCheckpt = &ethpb.Checkpoint{}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{})
 	require.NoError(t, s.checkSaveHotStateDB(context.Background()))
 	s.genesisTime = time.Now()

@@ -381,11 +315,11 @@ func TestCheckSaveHotStateDB_Disabling(t *testing.T) {
 }

 func TestCheckSaveHotStateDB_Overflow(t *testing.T) {
-	beaconDB := testDB.SetupDB(t)
 	hook := logTest.NewGlobal()
-	s, err := NewService(context.Background(), &Config{StateGen: stategen.New(beaconDB)})
+	opts := testServiceOptsWithDB(t)
+	s, err := NewService(context.Background(), opts...)
 	require.NoError(t, err)
-	s.finalizedCheckpt = &ethpb.Checkpoint{Epoch: 10000000}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 10000000})
 	s.genesisTime = time.Now()

 	require.NoError(t, s.checkSaveHotStateDB(context.Background()))
--- a/beacon-chain/blockchain/service.go
+++ b/beacon-chain/blockchain/service.go
@@ -11,28 +11,33 @@ import (

 	"github.com/pkg/errors"
 	types "github.com/prysmaticlabs/eth2-types"
+	"github.com/prysmaticlabs/prysm/async/event"
+	"github.com/prysmaticlabs/prysm/beacon-chain/blockchain/store"
 	"github.com/prysmaticlabs/prysm/beacon-chain/cache"
 	"github.com/prysmaticlabs/prysm/beacon-chain/cache/depositcache"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/feed"
 	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/beacon-chain/db"
 	f "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice"
+	doublylinkedtree "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/doubly-linked-tree"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/attestations"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/slashings"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/voluntaryexits"
 	"github.com/prysmaticlabs/prysm/beacon-chain/p2p"
 	"github.com/prysmaticlabs/prysm/beacon-chain/powchain"
+	enginev1 "github.com/prysmaticlabs/prysm/beacon-chain/powchain/engine-api-client/v1"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
 	"github.com/prysmaticlabs/prysm/cmd/beacon-chain/flags"
+	"github.com/prysmaticlabs/prysm/config/features"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	prysmTime "github.com/prysmaticlabs/prysm/time"
 	"github.com/prysmaticlabs/prysm/time/slots"
 	"github.com/sirupsen/logrus"
 	"go.opencensus.io/trace"
@@ -45,30 +50,26 @@ const headSyncMinEpochsAfterCheckpoint = 128
 // Service represents a service that handles the internal
 // logic of managing the full PoS beacon chain.
 type Service struct {
-	cfg                   *Config
-	ctx                   context.Context
-	cancel                context.CancelFunc
-	genesisTime           time.Time
-	head                  *head
-	headLock              sync.RWMutex
-	genesisRoot           [32]byte
-	justifiedCheckpt      *ethpb.Checkpoint
-	prevJustifiedCheckpt  *ethpb.Checkpoint
-	bestJustifiedCheckpt  *ethpb.Checkpoint
-	finalizedCheckpt      *ethpb.Checkpoint
-	prevFinalizedCheckpt  *ethpb.Checkpoint
+	cfg         *config
+	ctx         context.Context
+	cancel      context.CancelFunc
+	genesisTime time.Time
+	head        *head
+	headLock    sync.RWMutex
+	// originBlockRoot is the genesis root, or weak subjectivity checkpoint root, depending on how the node is initialized
+	originBlockRoot       [32]byte
 	nextEpochBoundarySlot types.Slot
 	boundaryRoots         [][32]byte
 	checkpointStateCache  *cache.CheckpointStateCache
 	initSyncBlocks        map[[32]byte]block.SignedBeaconBlock
 	initSyncBlocksLock    sync.RWMutex
-	justifiedBalances     []uint64
-	justifiedBalancesLock sync.RWMutex
-	wsVerified            bool
+	justifiedBalances     *stateBalanceCache
+	wsVerifier            *WeakSubjectivityVerifier
+	store                 *store.Store
 }

-// Config options for the service.
-type Config struct {
+// config options for the service.
+type config struct {
 	BeaconBlockBuf          int
 	ChainStartFetcher       powchain.ChainStartFetcher
 	BeaconDB                db.HeadAccessDatabase
@@ -82,166 +83,288 @@ type Config struct {
 	ForkChoiceStore         f.ForkChoicer
 	AttService              *attestations.Service
 	StateGen                *stategen.State
+	SlasherAttestationsFeed *event.Feed
 	WeakSubjectivityCheckpt *ethpb.Checkpoint
+	BlockFetcher            powchain.POWBlockFetcher
+	FinalizedStateAtStartUp state.BeaconState
+	ExecutionEngineCaller   enginev1.Caller
 }

 // NewService instantiates a new block service instance that will
 // be registered into a running beacon node.
-func NewService(ctx context.Context, cfg *Config) (*Service, error) {
+func NewService(ctx context.Context, opts ...Option) (*Service, error) {
 	ctx, cancel := context.WithCancel(ctx)
-	return &Service{
-		cfg:                  cfg,
+	srv := &Service{
 		ctx:                  ctx,
 		cancel:               cancel,
 		boundaryRoots:        [][32]byte{},
 		checkpointStateCache: cache.NewCheckpointStateCache(),
 		initSyncBlocks:       make(map[[32]byte]block.SignedBeaconBlock),
-		justifiedBalances:    make([]uint64, 0),
-	}, nil
+		cfg:                  &config{},
+		store:                &store.Store{},
+	}
+	for _, opt := range opts {
+		if err := opt(srv); err != nil {
+			return nil, err
+		}
+	}
+	var err error
+	if srv.justifiedBalances == nil {
+		srv.justifiedBalances, err = newStateBalanceCache(srv.cfg.StateGen)
+		if err != nil {
+			return nil, err
+		}
+	}
+	srv.wsVerifier, err = NewWeakSubjectivityVerifier(srv.cfg.WeakSubjectivityCheckpt, srv.cfg.BeaconDB)
+	if err != nil {
+		return nil, err
+	}
+	return srv, nil
 }

 // Start a blockchain service's main event loop.
 func (s *Service) Start() {
-	// For running initial sync with state cache, in an event of restart, we use
-	// last finalized check point as start point to sync instead of head
-	// state. This is because we no longer save state every slot during sync.
-	cp, err := s.cfg.BeaconDB.FinalizedCheckpoint(s.ctx)
-	if err != nil {
-		log.Fatalf("Could not fetch finalized cp: %v", err)
-	}
+	saved := s.cfg.FinalizedStateAtStartUp

-	r := bytesutil.ToBytes32(cp.Root)
-	// Before the first finalized epoch, in the current epoch,
-	// the finalized root is defined as zero hashes instead of genesis root hash.
-	// We want to use genesis root to retrieve for state.
-	if r == params.BeaconConfig().ZeroHash {
-		genesisBlock, err := s.cfg.BeaconDB.GenesisBlock(s.ctx)
-		if err != nil {
-			log.Fatalf("Could not fetch finalized cp: %v", err)
+	if saved != nil && !saved.IsNil() {
+		if err := s.startFromSavedState(saved); err != nil {
+			log.Fatal(err)
 		}
-		if genesisBlock != nil && !genesisBlock.IsNil() {
-			r, err = genesisBlock.Block().HashTreeRoot()
-			if err != nil {
-				log.Fatalf("Could not tree hash genesis block: %v", err)
-			}
-		}
-	}
-	beaconState, err := s.cfg.StateGen.StateByRoot(s.ctx, r)
-	if err != nil {
-		log.Fatalf("Could not fetch beacon state by root: %v", err)
-	}
-
-	// Make sure that attestation processor is subscribed and ready for state initializing event.
-	attestationProcessorSubscribed := make(chan struct{}, 1)
-
-	// If the chain has already been initialized, simply start the block processing routine.
-	if beaconState != nil && !beaconState.IsNil() {
-		log.Info("Blockchain data already exists in DB, initializing...")
-		s.genesisTime = time.Unix(int64(beaconState.GenesisTime()), 0)
-		s.cfg.AttService.SetGenesisTime(beaconState.GenesisTime())
-		if err := s.initializeChainInfo(s.ctx); err != nil {
-			log.Fatalf("Could not set up chain info: %v", err)
-		}
-
-		// We start a counter to genesis, if needed.
-		gState, err := s.cfg.BeaconDB.GenesisState(s.ctx)
-		if err != nil {
-			log.Fatalf("Could not retrieve genesis state: %v", err)
-		}
-		gRoot, err := gState.HashTreeRoot(s.ctx)
-		if err != nil {
-			log.Fatalf("Could not hash tree root genesis state: %v", err)
-		}
-		go slots.CountdownToGenesis(s.ctx, s.genesisTime, uint64(gState.NumValidators()), gRoot)
-
-		justifiedCheckpoint, err := s.cfg.BeaconDB.JustifiedCheckpoint(s.ctx)
-		if err != nil {
-			log.Fatalf("Could not get justified checkpoint: %v", err)
-		}
-		finalizedCheckpoint, err := s.cfg.BeaconDB.FinalizedCheckpoint(s.ctx)
-		if err != nil {
-			log.Fatalf("Could not get finalized checkpoint: %v", err)
-		}
-
-		// Resume fork choice.
-		s.justifiedCheckpt = ethpb.CopyCheckpoint(justifiedCheckpoint)
-		if err := s.cacheJustifiedStateBalances(s.ctx, s.ensureRootNotZeros(bytesutil.ToBytes32(s.justifiedCheckpt.Root))); err != nil {
-			log.Fatalf("Could not cache justified state balances: %v", err)
-		}
-		s.prevJustifiedCheckpt = ethpb.CopyCheckpoint(justifiedCheckpoint)
-		s.bestJustifiedCheckpt = ethpb.CopyCheckpoint(justifiedCheckpoint)
-		s.finalizedCheckpt = ethpb.CopyCheckpoint(finalizedCheckpoint)
-		s.prevFinalizedCheckpt = ethpb.CopyCheckpoint(finalizedCheckpoint)
-		s.resumeForkChoice(justifiedCheckpoint, finalizedCheckpoint)
-
-		ss, err := core.StartSlot(s.finalizedCheckpt.Epoch)
-		if err != nil {
-			log.Fatalf("Could not get start slot of finalized epoch: %v", err)
-		}
-		h := s.headBlock().Block()
-		if h.Slot() > ss {
-			log.WithFields(logrus.Fields{
-				"startSlot": ss,
-				"endSlot":   h.Slot(),
-			}).Info("Loading blocks to fork choice store, this may take a while.")
-			if err := s.fillInForkChoiceMissingBlocks(s.ctx, h, s.finalizedCheckpt, s.justifiedCheckpt); err != nil {
-				log.Fatalf("Could not fill in fork choice store missing blocks: %v", err)
-			}
-		}
-
-		if err := s.VerifyWeakSubjectivityRoot(s.ctx); err != nil {
-			// Exit run time if the node failed to verify weak subjectivity checkpoint.
-			log.Fatalf("Could not verify weak subjectivity checkpoint: %v", err)
-		}
-
-		s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
-			Type: statefeed.Initialized,
-			Data: &statefeed.InitializedData{
-				StartTime:             s.genesisTime,
-				GenesisValidatorsRoot: beaconState.GenesisValidatorRoot(),
-			},
-		})
 	} else {
-		log.Info("Waiting to reach the validator deposit threshold to start the beacon chain...")
-		if s.cfg.ChainStartFetcher == nil {
-			log.Fatal("Not configured web3Service for POW chain")
-			return // return need for TestStartUninitializedChainWithoutConfigPOWChain.
+		if err := s.startFromPOWChain(); err != nil {
+			log.Fatal(err)
 		}
-		go func() {
-			stateChannel := make(chan *feed.Event, 1)
-			stateSub := s.cfg.StateNotifier.StateFeed().Subscribe(stateChannel)
-			defer stateSub.Unsubscribe()
-			<-attestationProcessorSubscribed
-			for {
-				select {
-				case event := <-stateChannel:
-					if event.Type == statefeed.ChainStarted {
-						data, ok := event.Data.(*statefeed.ChainStartedData)
-						if !ok {
-							log.Error("event data is not type *statefeed.ChainStartedData")
-							return
-						}
-						log.WithField("starttime", data.StartTime).Debug("Received chain start event")
-						s.processChainStartTime(s.ctx, data.StartTime)
-						return
-					}
-				case <-s.ctx.Done():
-					log.Debug("Context closed, exiting goroutine")
-					return
-				case err := <-stateSub.Err():
-					log.WithError(err).Error("Subscription to state notifier failed")
-					return
-				}
-			}
-		}()
 	}
-
-	go s.processAttestationsRoutine(attestationProcessorSubscribed)
+	s.spawnProcessAttestationsRoutine(s.cfg.StateNotifier.StateFeed())
 }

-// processChainStartTime initializes a series of deposits from the ChainStart deposits in the eth1
+// Stop the blockchain service's main event loop and associated goroutines.
+func (s *Service) Stop() error {
+	defer s.cancel()
+
+	if s.cfg.StateGen != nil && s.head != nil && s.head.state != nil {
+		if err := s.cfg.StateGen.ForceCheckpoint(s.ctx, s.head.state.FinalizedCheckpoint().Root); err != nil {
+			return err
+		}
+	}
+
+	// Save initial sync cached blocks to the DB before stop.
+	return s.cfg.BeaconDB.SaveBlocks(s.ctx, s.getInitSyncBlocks())
+}
+
+// Status always returns nil unless there is an error condition that causes
+// this service to be unhealthy.
+func (s *Service) Status() error {
+	if s.originBlockRoot == params.BeaconConfig().ZeroHash {
+		return errors.New("genesis state has not been created")
+	}
+	if runtime.NumGoroutine() > s.cfg.MaxRoutines {
+		return fmt.Errorf("too many goroutines %d", runtime.NumGoroutine())
+	}
+	return nil
+}
+
+func (s *Service) startFromSavedState(saved state.BeaconState) error {
+	log.Info("Blockchain data already exists in DB, initializing...")
+	s.genesisTime = time.Unix(int64(saved.GenesisTime()), 0)
+	s.cfg.AttService.SetGenesisTime(saved.GenesisTime())
+
+	originRoot, err := s.originRootFromSavedState(s.ctx)
+	if err != nil {
+		return err
+	}
+	s.originBlockRoot = originRoot
+
+	if err := s.initializeHeadFromDB(s.ctx); err != nil {
+		return errors.Wrap(err, "could not set up chain info")
+	}
+	spawnCountdownIfPreGenesis(s.ctx, s.genesisTime, s.cfg.BeaconDB)
+
+	justified, err := s.cfg.BeaconDB.JustifiedCheckpoint(s.ctx)
+	if err != nil {
+		return errors.Wrap(err, "could not get justified checkpoint")
+	}
+	finalized, err := s.cfg.BeaconDB.FinalizedCheckpoint(s.ctx)
+	if err != nil {
+		return errors.Wrap(err, "could not get finalized checkpoint")
+	}
+	s.store = store.New(justified, finalized)
+
+	var store f.ForkChoicer
+	if features.Get().EnableForkChoiceDoublyLinkedTree {
+		store = doublylinkedtree.New(justified.Epoch, finalized.Epoch)
+	} else {
+		store = protoarray.New(justified.Epoch, finalized.Epoch, bytesutil.ToBytes32(finalized.Root))
+	}
+	s.cfg.ForkChoiceStore = store
+
+	ss, err := slots.EpochStart(finalized.Epoch)
+	if err != nil {
+		return errors.Wrap(err, "could not get start slot of finalized epoch")
+	}
+	h := s.headBlock().Block()
+	if h.Slot() > ss {
+		log.WithFields(logrus.Fields{
+			"startSlot": ss,
+			"endSlot":   h.Slot(),
+		}).Info("Loading blocks to fork choice store, this may take a while.")
+		if err := s.fillInForkChoiceMissingBlocks(s.ctx, h, finalized, justified); err != nil {
+			return errors.Wrap(err, "could not fill in fork choice store missing blocks")
+		}
+	}
+
+	// not attempting to save initial sync blocks here, because there shouldn't be any until
+	// after the statefeed.Initialized event is fired (below)
+	if err := s.wsVerifier.VerifyWeakSubjectivity(s.ctx, finalized.Epoch); err != nil {
+		// Exit run time if the node failed to verify weak subjectivity checkpoint.
+		return errors.Wrap(err, "could not verify initial checkpoint provided for chain sync")
+	}
+
+	s.cfg.StateNotifier.StateFeed().Send(&feed.Event{
+		Type: statefeed.Initialized,
+		Data: &statefeed.InitializedData{
+			StartTime:             s.genesisTime,
+			GenesisValidatorsRoot: saved.GenesisValidatorsRoot(),
+		},
+	})
+
+	return nil
+}
+
+func (s *Service) originRootFromSavedState(ctx context.Context) ([32]byte, error) {
+	// first check if we have started from checkpoint sync and have a root
+	originRoot, err := s.cfg.BeaconDB.OriginBlockRoot(ctx)
+	if err == nil {
+		return originRoot, nil
+	}
+	if !errors.Is(err, db.ErrNotFound) {
+		return originRoot, errors.Wrap(err, "could not retrieve checkpoint sync chain origin data from db")
+	}
+
+	// we got here because OriginBlockRoot gave us an ErrNotFound. this means the node was started from a genesis state,
+	// so we should have a value for GenesisBlock
+	genesisBlock, err := s.cfg.BeaconDB.GenesisBlock(ctx)
+	if err != nil {
+		return originRoot, errors.Wrap(err, "could not get genesis block from db")
+	}
+	if err := helpers.BeaconBlockIsNil(genesisBlock); err != nil {
+		return originRoot, err
+	}
+	genesisBlkRoot, err := genesisBlock.Block().HashTreeRoot()
+	if err != nil {
+		return genesisBlkRoot, errors.Wrap(err, "could not get signing root of genesis block")
+	}
+	return genesisBlkRoot, nil
+}
+
+// initializeHeadFromDB uses the finalized checkpoint and head block found in the database to set the current head
+// note that this may block until stategen replays blocks between the finalized and head blocks
+// if the head sync flag was specified and the gap between the finalized and head blocks is at least 128 epochs long
+func (s *Service) initializeHeadFromDB(ctx context.Context) error {
+	finalized, err := s.cfg.BeaconDB.FinalizedCheckpoint(ctx)
+	if err != nil {
+		return errors.Wrap(err, "could not get finalized checkpoint from db")
+	}
+	if finalized == nil {
+		// This should never happen. At chain start, the finalized checkpoint
+		// would be the genesis state and block.
+		return errors.New("no finalized epoch in the database")
+	}
+	finalizedRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(finalized.Root))
+	var finalizedState state.BeaconState
+
+	finalizedState, err = s.cfg.StateGen.Resume(ctx, s.cfg.FinalizedStateAtStartUp)
+	if err != nil {
+		return errors.Wrap(err, "could not get finalized state from db")
+	}
+
+	if flags.Get().HeadSync {
+		headBlock, err := s.cfg.BeaconDB.HeadBlock(ctx)
+		if err != nil {
+			return errors.Wrap(err, "could not retrieve head block")
+		}
+		headEpoch := slots.ToEpoch(headBlock.Block().Slot())
+		var epochsSinceFinality types.Epoch
+		if headEpoch > finalized.Epoch {
+			epochsSinceFinality = headEpoch - finalized.Epoch
+		}
+		// Head sync when node is far enough beyond known finalized epoch,
+		// this becomes really useful during long period of non-finality.
+		if epochsSinceFinality >= headSyncMinEpochsAfterCheckpoint {
+			headRoot, err := headBlock.Block().HashTreeRoot()
+			if err != nil {
+				return errors.Wrap(err, "could not hash head block")
+			}
+			finalizedState, err := s.cfg.StateGen.Resume(ctx, s.cfg.FinalizedStateAtStartUp)
+			if err != nil {
+				return errors.Wrap(err, "could not get finalized state from db")
+			}
+			log.Infof("Regenerating state from the last checkpoint at slot %d to current head slot of %d."+
+				"This process may take a while, please wait.", finalizedState.Slot(), headBlock.Block().Slot())
+			headState, err := s.cfg.StateGen.StateByRoot(ctx, headRoot)
+			if err != nil {
+				return errors.Wrap(err, "could not retrieve head state")
+			}
+			s.setHead(headRoot, headBlock, headState)
+			return nil
+		} else {
+			log.Warnf("Finalized checkpoint at slot %d is too close to the current head slot, "+
+				"resetting head from the checkpoint ('--%s' flag is ignored).",
+				finalizedState.Slot(), flags.HeadSync.Name)
+		}
+	}
+
+	finalizedBlock, err := s.cfg.BeaconDB.Block(ctx, finalizedRoot)
+	if err != nil {
+		return errors.Wrap(err, "could not get finalized block from db")
+	}
+
+	if finalizedState == nil || finalizedState.IsNil() || finalizedBlock == nil || finalizedBlock.IsNil() {
+		return errors.New("finalized state and block can't be nil")
+	}
+	s.setHead(finalizedRoot, finalizedBlock, finalizedState)
+
+	return nil
+}
+
+func (s *Service) startFromPOWChain() error {
+	log.Info("Waiting to reach the validator deposit threshold to start the beacon chain...")
+	if s.cfg.ChainStartFetcher == nil {
+		return errors.New("not configured web3Service for POW chain")
+	}
+	go func() {
+		stateChannel := make(chan *feed.Event, 1)
+		stateSub := s.cfg.StateNotifier.StateFeed().Subscribe(stateChannel)
+		defer stateSub.Unsubscribe()
+		for {
+			select {
+			case event := <-stateChannel:
+				if event.Type == statefeed.ChainStarted {
+					data, ok := event.Data.(*statefeed.ChainStartedData)
+					if !ok {
+						log.Error("event data is not type *statefeed.ChainStartedData")
+						return
+					}
+					log.WithField("starttime", data.StartTime).Debug("Received chain start event")
+					s.onPowchainStart(s.ctx, data.StartTime)
+					return
+				}
+			case <-s.ctx.Done():
+				log.Debug("Context closed, exiting goroutine")
+				return
+			case err := <-stateSub.Err():
+				log.WithError(err).Error("Subscription to state notifier failed")
+				return
+			}
+		}
+	}()
+
+	return nil
+}
+
+// onPowchainStart initializes a series of deposits from the ChainStart deposits in the eth1
 // deposit contract, initializes the beacon chain's state, and kicks off the beacon chain.
-func (s *Service) processChainStartTime(ctx context.Context, genesisTime time.Time) {
+func (s *Service) onPowchainStart(ctx context.Context, genesisTime time.Time) {
 	preGenesisState := s.cfg.ChainStartFetcher.PreGenesisState()
 	initializedState, err := s.initializeBeaconChain(ctx, genesisTime, preGenesisState, s.cfg.ChainStartFetcher.ChainStartEth1Data())
 	if err != nil {
@@ -260,7 +383,7 @@ func (s *Service) processChainStartTime(ctx context.Context, genesisTime time.Ti
 		Type: statefeed.Initialized,
 		Data: &statefeed.InitializedData{
 			StartTime:             genesisTime,
-			GenesisValidatorsRoot: initializedState.GenesisValidatorRoot(),
+			GenesisValidatorsRoot: initializedState.GenesisValidatorsRoot(),
 		},
 	})
 }
@@ -296,7 +419,7 @@ func (s *Service) initializeBeaconChain(
 	if err := helpers.UpdateCommitteeCache(genesisState, 0 /* genesis epoch */); err != nil {
 		return nil, err
 	}
-	if err := helpers.UpdateProposerIndicesInCache(genesisState); err != nil {
+	if err := helpers.UpdateProposerIndicesInCache(ctx, genesisState); err != nil {
 		return nil, err
 	}

@@ -305,32 +428,6 @@ func (s *Service) initializeBeaconChain(
 	return genesisState, nil
 }

-// Stop the blockchain service's main event loop and associated goroutines.
-func (s *Service) Stop() error {
-	defer s.cancel()
-
-	if s.cfg.StateGen != nil && s.head != nil && s.head.state != nil {
-		if err := s.cfg.StateGen.ForceCheckpoint(s.ctx, s.head.state.FinalizedCheckpoint().Root); err != nil {
-			return err
-		}
-	}
-
-	// Save initial sync cached blocks to the DB before stop.
-	return s.cfg.BeaconDB.SaveBlocks(s.ctx, s.getInitSyncBlocks())
-}
-
-// Status always returns nil unless there is an error condition that causes
-// this service to be unhealthy.
-func (s *Service) Status() error {
-	if s.genesisRoot == params.BeaconConfig().ZeroHash {
-		return errors.New("genesis state has not been created")
-	}
-	if runtime.NumGoroutine() > s.cfg.MaxRoutines {
-		return fmt.Errorf("too many goroutines %d", runtime.NumGoroutine())
-	}
-	return nil
-}
-
 // This gets called when beacon chain is first initialized to save genesis data (state, block, and more) in db.
 func (s *Service) saveGenesisData(ctx context.Context, genesisState state.BeaconState) error {
 	if err := s.cfg.BeaconDB.SaveGenesisData(ctx, genesisState); err != nil {
@@ -345,28 +442,19 @@ func (s *Service) saveGenesisData(ctx context.Context, genesisState state.Beacon
 		return errors.Wrap(err, "could not get genesis block root")
 	}

-	s.genesisRoot = genesisBlkRoot
+	s.originBlockRoot = genesisBlkRoot
 	s.cfg.StateGen.SaveFinalizedState(0 /*slot*/, genesisBlkRoot, genesisState)

 	// Finalized checkpoint at genesis is a zero hash.
 	genesisCheckpoint := genesisState.FinalizedCheckpoint()
-
-	s.justifiedCheckpt = ethpb.CopyCheckpoint(genesisCheckpoint)
-	if err := s.cacheJustifiedStateBalances(ctx, genesisBlkRoot); err != nil {
-		return err
-	}
-	s.prevJustifiedCheckpt = ethpb.CopyCheckpoint(genesisCheckpoint)
-	s.bestJustifiedCheckpt = ethpb.CopyCheckpoint(genesisCheckpoint)
-	s.finalizedCheckpt = ethpb.CopyCheckpoint(genesisCheckpoint)
-	s.prevFinalizedCheckpt = ethpb.CopyCheckpoint(genesisCheckpoint)
+	s.store = store.New(genesisCheckpoint, genesisCheckpoint)

 	if err := s.cfg.ForkChoiceStore.ProcessBlock(ctx,
 		genesisBlk.Block().Slot(),
 		genesisBlkRoot,
 		params.BeaconConfig().ZeroHash,
-		[32]byte{},
 		genesisCheckpoint.Epoch,
-		genesisCheckpoint.Epoch); err != nil {
+		genesisCheckpoint.Epoch, false /* optimistic status */); err != nil {
 		log.Fatalf("Could not process genesis block for fork choice: %v", err)
 	}

@@ -374,94 +462,6 @@ func (s *Service) saveGenesisData(ctx context.Context, genesisState state.Beacon
 	return nil
 }

-// This gets called to initialize chain info variables using the finalized checkpoint stored in DB
-func (s *Service) initializeChainInfo(ctx context.Context) error {
-	genesisBlock, err := s.cfg.BeaconDB.GenesisBlock(ctx)
-	if err != nil {
-		return errors.Wrap(err, "could not get genesis block from db")
-	}
-	if genesisBlock == nil || genesisBlock.IsNil() {
-		return errors.New("no genesis block in db")
-	}
-	genesisBlkRoot, err := genesisBlock.Block().HashTreeRoot()
-	if err != nil {
-		return errors.Wrap(err, "could not get signing root of genesis block")
-	}
-	s.genesisRoot = genesisBlkRoot
-
-	finalized, err := s.cfg.BeaconDB.FinalizedCheckpoint(ctx)
-	if err != nil {
-		return errors.Wrap(err, "could not get finalized checkpoint from db")
-	}
-	if finalized == nil {
-		// This should never happen. At chain start, the finalized checkpoint
-		// would be the genesis state and block.
-		return errors.New("no finalized epoch in the database")
-	}
-	finalizedRoot := s.ensureRootNotZeros(bytesutil.ToBytes32(finalized.Root))
-	var finalizedState state.BeaconState
-
-	finalizedState, err = s.cfg.StateGen.Resume(ctx)
-	if err != nil {
-		return errors.Wrap(err, "could not get finalized state from db")
-	}
-
-	if flags.Get().HeadSync {
-		headBlock, err := s.cfg.BeaconDB.HeadBlock(ctx)
-		if err != nil {
-			return errors.Wrap(err, "could not retrieve head block")
-		}
-		headEpoch := core.SlotToEpoch(headBlock.Block().Slot())
-		var epochsSinceFinality types.Epoch
-		if headEpoch > finalized.Epoch {
-			epochsSinceFinality = headEpoch - finalized.Epoch
-		}
-		// Head sync when node is far enough beyond known finalized epoch,
-		// this becomes really useful during long period of non-finality.
-		if epochsSinceFinality >= headSyncMinEpochsAfterCheckpoint {
-			headRoot, err := headBlock.Block().HashTreeRoot()
-			if err != nil {
-				return errors.Wrap(err, "could not hash head block")
-			}
-			finalizedState, err := s.cfg.StateGen.Resume(ctx)
-			if err != nil {
-				return errors.Wrap(err, "could not get finalized state from db")
-			}
-			log.Infof("Regenerating state from the last checkpoint at slot %d to current head slot of %d."+
-				"This process may take a while, please wait.", finalizedState.Slot(), headBlock.Block().Slot())
-			headState, err := s.cfg.StateGen.StateByRoot(ctx, headRoot)
-			if err != nil {
-				return errors.Wrap(err, "could not retrieve head state")
-			}
-			s.setHead(headRoot, headBlock, headState)
-			return nil
-		} else {
-			log.Warnf("Finalized checkpoint at slot %d is too close to the current head slot, "+
-				"resetting head from the checkpoint ('--%s' flag is ignored).",
-				finalizedState.Slot(), flags.HeadSync.Name)
-		}
-	}
-
-	finalizedBlock, err := s.cfg.BeaconDB.Block(ctx, finalizedRoot)
-	if err != nil {
-		return errors.Wrap(err, "could not get finalized block from db")
-	}
-
-	if finalizedState == nil || finalizedState.IsNil() || finalizedBlock == nil || finalizedBlock.IsNil() {
-		return errors.New("finalized state and block can't be nil")
-	}
-	s.setHead(finalizedRoot, finalizedBlock, finalizedState)
-
-	return nil
-}
-
-// This is called when a client starts from non-genesis slot. This passes last justified and finalized
-// information to fork choice service to initializes fork choice store.
-func (s *Service) resumeForkChoice(justifiedCheckpoint, finalizedCheckpoint *ethpb.Checkpoint) {
-	store := protoarray.New(justifiedCheckpoint.Epoch, finalizedCheckpoint.Epoch, bytesutil.ToBytes32(finalizedCheckpoint.Root))
-	s.cfg.ForkChoiceStore = store
-}
-
 // This returns true if block has been processed before. Two ways to verify the block has been processed:
 // 1.) Check fork choice store.
 // 2.) Check DB.
@@ -473,3 +473,20 @@ func (s *Service) hasBlock(ctx context.Context, root [32]byte) bool {

 	return s.cfg.BeaconDB.HasBlock(ctx, root)
 }
+
+func spawnCountdownIfPreGenesis(ctx context.Context, genesisTime time.Time, db db.HeadAccessDatabase) {
+	currentTime := prysmTime.Now()
+	if currentTime.After(genesisTime) {
+		return
+	}
+
+	gState, err := db.GenesisState(ctx)
+	if err != nil {
+		log.Fatalf("Could not retrieve genesis state: %v", err)
+	}
+	gRoot, err := gState.HashTreeRoot(ctx)
+	if err != nil {
+		log.Fatalf("Could not hash tree root genesis state: %v", err)
+	}
+	go slots.CountdownToGenesis(ctx, genesisTime, uint64(gState.NumValidators()), gRoot)
+}
--- a/beacon-chain/blockchain/service_norace_test.go
+++ b/beacon-chain/blockchain/service_norace_test.go
@@ -6,7 +6,7 @@ import (
 	"testing"

 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	"github.com/sirupsen/logrus"
 )

@@ -18,7 +18,7 @@ func init() {
 func TestChainService_SaveHead_DataRace(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg: &Config{BeaconDB: beaconDB},
+		cfg: &config{BeaconDB: beaconDB},
 	}
 	go func() {
 		require.NoError(t, s.saveHead(context.Background(), [32]byte{}))
--- a/beacon-chain/blockchain/service_test.go
+++ b/beacon-chain/blockchain/service_test.go
@@ -9,8 +9,9 @@ import (

 	"github.com/ethereum/go-ethereum/common"
 	"github.com/prysmaticlabs/prysm/async/event"
+	"github.com/prysmaticlabs/prysm/beacon-chain/blockchain/store"
+	mock "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing"
 	"github.com/prysmaticlabs/prysm/beacon-chain/cache/depositcache"
-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
 	b "github.com/prysmaticlabs/prysm/beacon-chain/core/blocks"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/feed"
 	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
@@ -18,6 +19,7 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/transition"
 	"github.com/prysmaticlabs/prysm/beacon-chain/db"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	doublylinkedtree "github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/doubly-linked-tree"
 	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
 	"github.com/prysmaticlabs/prysm/beacon-chain/operations/attestations"
 	"github.com/prysmaticlabs/prysm/beacon-chain/p2p"
@@ -25,14 +27,15 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
 	v1 "github.com/prysmaticlabs/prysm/beacon-chain/state/v1"
 	"github.com/prysmaticlabs/prysm/cmd/beacon-chain/flags"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
+	"github.com/prysmaticlabs/prysm/time/slots"
 	logTest "github.com/sirupsen/logrus/hooks/test"
 	"google.golang.org/protobuf/proto"
 )
@@ -75,7 +78,7 @@ func setupBeaconChain(t *testing.T, beaconDB db.Database) *Service {
 	ctx := context.Background()
 	var web3Service *powchain.Service
 	var err error
-	bState, _ := testutil.DeterministicGenesisState(t, 10)
+	bState, _ := util.DeterministicGenesisState(t, 10)
 	pbState, err := v1.ProtobufBeaconState(bState.InnerStateUnsafe())
 	require.NoError(t, err)
 	err = beaconDB.SavePowchainData(ctx, &ethpb.ETH1ChainData{
@@ -94,11 +97,12 @@ func setupBeaconChain(t *testing.T, beaconDB db.Database) *Service {
 		DepositContainers: []*ethpb.DepositContainer{},
 	})
 	require.NoError(t, err)
-	web3Service, err = powchain.NewService(ctx, &powchain.Web3ServiceConfig{
-		BeaconDB:        beaconDB,
-		HttpEndpoints:   []string{endpoint},
-		DepositContract: common.Address{},
-	})
+	web3Service, err = powchain.NewService(
+		ctx,
+		powchain.WithDatabase(beaconDB),
+		powchain.WithHttpEndpoints([]string{endpoint}),
+		powchain.WithDepositContractAddress(common.Address{}),
+	)
 	require.NoError(t, err, "Unable to set up web3 service")

 	attService, err := attestations.NewService(ctx, &attestations.Config{Pool: attestations.NewPool()})
@@ -107,23 +111,23 @@ func setupBeaconChain(t *testing.T, beaconDB db.Database) *Service {
 	depositCache, err := depositcache.New()
 	require.NoError(t, err)

-	cfg := &Config{
-		BeaconBlockBuf:    0,
-		BeaconDB:          beaconDB,
-		DepositCache:      depositCache,
-		ChainStartFetcher: web3Service,
-		P2p:               &mockBroadcaster{},
-		StateNotifier:     &mockBeaconNode{},
-		AttPool:           attestations.NewPool(),
-		StateGen:          stategen.New(beaconDB),
-		ForkChoiceStore:   protoarray.New(0, 0, params.BeaconConfig().ZeroHash),
-		AttService:        attService,
+	stateGen := stategen.New(beaconDB)
+	// Safe a state in stategen to purposes of testing a service stop / shutdown.
+	require.NoError(t, stateGen.SaveState(ctx, bytesutil.ToBytes32(bState.FinalizedCheckpoint().Root), bState))
+
+	opts := []Option{
+		WithDatabase(beaconDB),
+		WithDepositCache(depositCache),
+		WithChainStartFetcher(web3Service),
+		WithAttestationPool(attestations.NewPool()),
+		WithP2PBroadcaster(&mockBroadcaster{}),
+		WithStateNotifier(&mockBeaconNode{}),
+		WithForkChoiceStore(protoarray.New(0, 0, params.BeaconConfig().ZeroHash)),
+		WithAttestationService(attService),
+		WithStateGen(stateGen),
 	}

-	// Safe a state in stategen to purposes of testing a service stop / shutdown.
-	require.NoError(t, cfg.StateGen.SaveState(ctx, bytesutil.ToBytes32(bState.FinalizedCheckpoint().Root), bState))
-
-	chainService, err := NewService(ctx, cfg)
+	chainService, err := NewService(ctx, opts...)
 	require.NoError(t, err, "Unable to setup chain service")
 	chainService.genesisTime = time.Unix(1, 0) // non-zero time

@@ -137,11 +141,11 @@ func TestChainStartStop_Initialized(t *testing.T) {

 	chainService := setupBeaconChain(t, beaconDB)

-	genesisBlk := testutil.NewBeaconBlock()
+	genesisBlk := util.NewBeaconBlock()
 	blkRoot, err := genesisBlk.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(genesisBlk)))
-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, s.SetSlot(1))
 	require.NoError(t, beaconDB.SaveState(ctx, s, blkRoot))
@@ -149,7 +153,7 @@ func TestChainStartStop_Initialized(t *testing.T) {
 	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, blkRoot))
 	require.NoError(t, beaconDB.SaveJustifiedCheckpoint(ctx, &ethpb.Checkpoint{Root: blkRoot[:]}))
 	require.NoError(t, beaconDB.SaveFinalizedCheckpoint(ctx, &ethpb.Checkpoint{Root: blkRoot[:]}))
-
+	chainService.cfg.FinalizedStateAtStartUp = s
 	// Test the start function.
 	chainService.Start()

@@ -167,16 +171,16 @@ func TestChainStartStop_GenesisZeroHashes(t *testing.T) {

 	chainService := setupBeaconChain(t, beaconDB)

-	genesisBlk := testutil.NewBeaconBlock()
+	genesisBlk := util.NewBeaconBlock()
 	blkRoot, err := genesisBlk.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(genesisBlk)))
-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveState(ctx, s, blkRoot))
 	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, blkRoot))
 	require.NoError(t, beaconDB.SaveJustifiedCheckpoint(ctx, &ethpb.Checkpoint{Root: params.BeaconConfig().ZeroHash[:]}))
-
+	chainService.cfg.FinalizedStateAtStartUp = s
 	// Test the start function.
 	chainService.Start()

@@ -197,9 +201,9 @@ func TestChainService_InitializeBeaconChain(t *testing.T) {

 	// Set up 10 deposits pre chain start for validators to register
 	count := uint64(10)
-	deposits, _, err := testutil.DeterministicDepositsAndKeys(count)
+	deposits, _, err := util.DeterministicDepositsAndKeys(count)
 	require.NoError(t, err)
-	trie, _, err := testutil.DepositTrieFromDeposits(deposits)
+	trie, _, err := util.DepositTrieFromDeposits(deposits)
 	require.NoError(t, err)
 	hashTreeRoot := trie.HashTreeRoot()
 	genState, err := transition.EmptyGenesisState()
@@ -236,23 +240,23 @@ func TestChainService_CorrectGenesisRoots(t *testing.T) {

 	chainService := setupBeaconChain(t, beaconDB)

-	genesisBlk := testutil.NewBeaconBlock()
+	genesisBlk := util.NewBeaconBlock()
 	blkRoot, err := genesisBlk.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(genesisBlk)))
-	s, err := testutil.NewBeaconState()
+	s, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, s.SetSlot(0))
 	require.NoError(t, beaconDB.SaveState(ctx, s, blkRoot))
 	require.NoError(t, beaconDB.SaveHeadBlockRoot(ctx, blkRoot))
 	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, blkRoot))
 	require.NoError(t, beaconDB.SaveFinalizedCheckpoint(ctx, &ethpb.Checkpoint{Root: blkRoot[:]}))
-
+	chainService.cfg.FinalizedStateAtStartUp = s
 	// Test the start function.
 	chainService.Start()

-	require.DeepEqual(t, blkRoot[:], chainService.finalizedCheckpt.Root, "Finalize Checkpoint root is incorrect")
-	require.DeepEqual(t, params.BeaconConfig().ZeroHash[:], chainService.justifiedCheckpt.Root, "Justified Checkpoint root is incorrect")
+	require.DeepEqual(t, blkRoot[:], chainService.store.FinalizedCheckpt().Root, "Finalize Checkpoint root is incorrect")
+	require.DeepEqual(t, params.BeaconConfig().ZeroHash[:], chainService.store.JustifiedCheckpt().Root, "Justified Checkpoint root is incorrect")

 	require.NoError(t, chainService.Stop(), "Unable to stop chain service")

@@ -262,28 +266,31 @@ func TestChainService_InitializeChainInfo(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	ctx := context.Background()

-	genesis := testutil.NewBeaconBlock()
+	genesis := util.NewBeaconBlock()
 	genesisRoot, err := genesis.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, genesisRoot))
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(genesis)))

 	finalizedSlot := params.BeaconConfig().SlotsPerEpoch*2 + 1
-	headBlock := testutil.NewBeaconBlock()
+	headBlock := util.NewBeaconBlock()
 	headBlock.Block.Slot = finalizedSlot
 	headBlock.Block.ParentRoot = bytesutil.PadTo(genesisRoot[:], 32)
-	headState, err := testutil.NewBeaconState()
+	headState, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, headState.SetSlot(finalizedSlot))
-	require.NoError(t, headState.SetGenesisValidatorRoot(params.BeaconConfig().ZeroHash[:]))
+	require.NoError(t, headState.SetGenesisValidatorsRoot(params.BeaconConfig().ZeroHash[:]))
 	headRoot, err := headBlock.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveState(ctx, headState, headRoot))
 	require.NoError(t, beaconDB.SaveState(ctx, headState, genesisRoot))
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(headBlock)))
-	require.NoError(t, beaconDB.SaveFinalizedCheckpoint(ctx, &ethpb.Checkpoint{Epoch: core.SlotToEpoch(finalizedSlot), Root: headRoot[:]}))
-	c := &Service{cfg: &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)}}
-	require.NoError(t, c.initializeChainInfo(ctx))
+	require.NoError(t, beaconDB.SaveFinalizedCheckpoint(ctx, &ethpb.Checkpoint{Epoch: slots.ToEpoch(finalizedSlot), Root: headRoot[:]}))
+	attSrv, err := attestations.NewService(ctx, &attestations.Config{})
+	require.NoError(t, err)
+	c, err := NewService(ctx, WithDatabase(beaconDB), WithStateGen(stategen.New(beaconDB)), WithAttestationService(attSrv), WithStateNotifier(&mock.MockStateNotifier{}), WithFinalizedStateAtStartUp(headState))
+	require.NoError(t, err)
+	require.NoError(t, c.startFromSavedState(headState))
 	headBlk, err := c.HeadBlock(ctx)
 	require.NoError(t, err)
 	assert.DeepEqual(t, headBlock, headBlk.Proto(), "Head block incorrect")
@@ -296,38 +303,41 @@ func TestChainService_InitializeChainInfo(t *testing.T) {
 	if !bytes.Equal(headRoot[:], r) {
 		t.Error("head slot incorrect")
 	}
-	assert.Equal(t, genesisRoot, c.genesisRoot, "Genesis block root incorrect")
+	assert.Equal(t, genesisRoot, c.originBlockRoot, "Genesis block root incorrect")
 }

 func TestChainService_InitializeChainInfo_SetHeadAtGenesis(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	ctx := context.Background()

-	genesis := testutil.NewBeaconBlock()
+	genesis := util.NewBeaconBlock()
 	genesisRoot, err := genesis.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, genesisRoot))
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(genesis)))

 	finalizedSlot := params.BeaconConfig().SlotsPerEpoch*2 + 1
-	headBlock := testutil.NewBeaconBlock()
+	headBlock := util.NewBeaconBlock()
 	headBlock.Block.Slot = finalizedSlot
 	headBlock.Block.ParentRoot = bytesutil.PadTo(genesisRoot[:], 32)
-	headState, err := testutil.NewBeaconState()
+	headState, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, headState.SetSlot(finalizedSlot))
-	require.NoError(t, headState.SetGenesisValidatorRoot(params.BeaconConfig().ZeroHash[:]))
+	require.NoError(t, headState.SetGenesisValidatorsRoot(params.BeaconConfig().ZeroHash[:]))
 	headRoot, err := headBlock.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveState(ctx, headState, headRoot))
 	require.NoError(t, beaconDB.SaveState(ctx, headState, genesisRoot))
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(headBlock)))
-	c := &Service{cfg: &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)}}
-	require.NoError(t, c.initializeChainInfo(ctx))
+	attSrv, err := attestations.NewService(ctx, &attestations.Config{})
+	require.NoError(t, err)
+	c, err := NewService(ctx, WithDatabase(beaconDB), WithStateGen(stategen.New(beaconDB)), WithAttestationService(attSrv), WithStateNotifier(&mock.MockStateNotifier{}))
+	require.NoError(t, err)
+	require.NoError(t, c.startFromSavedState(headState))
 	s, err := c.HeadState(ctx)
 	require.NoError(t, err)
 	assert.DeepSSZEqual(t, headState.InnerStateUnsafe(), s.InnerStateUnsafe(), "Head state incorrect")
-	assert.Equal(t, genesisRoot, c.genesisRoot, "Genesis block root incorrect")
+	assert.Equal(t, genesisRoot, c.originBlockRoot, "Genesis block root incorrect")
 	assert.DeepEqual(t, genesis, c.head.block.Proto())
 }

@@ -345,13 +355,13 @@ func TestChainService_InitializeChainInfo_HeadSync(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	ctx := context.Background()

-	genesisBlock := testutil.NewBeaconBlock()
+	genesisBlock := util.NewBeaconBlock()
 	genesisRoot, err := genesisBlock.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveGenesisBlockRoot(ctx, genesisRoot))
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(genesisBlock)))

-	finalizedBlock := testutil.NewBeaconBlock()
+	finalizedBlock := util.NewBeaconBlock()
 	finalizedBlock.Block.Slot = finalizedSlot
 	finalizedBlock.Block.ParentRoot = genesisRoot[:]
 	finalizedRoot, err := finalizedBlock.Block.HashTreeRoot()
@@ -359,40 +369,42 @@ func TestChainService_InitializeChainInfo_HeadSync(t *testing.T) {
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(finalizedBlock)))

 	// Set head slot close to the finalization point, no head sync is triggered.
-	headBlock := testutil.NewBeaconBlock()
+	headBlock := util.NewBeaconBlock()
 	headBlock.Block.Slot = finalizedSlot + params.BeaconConfig().SlotsPerEpoch*5
 	headBlock.Block.ParentRoot = finalizedRoot[:]
 	headRoot, err := headBlock.Block.HashTreeRoot()
 	require.NoError(t, err)
 	require.NoError(t, beaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(headBlock)))

-	headState, err := testutil.NewBeaconState()
+	headState, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, headState.SetSlot(headBlock.Block.Slot))
-	require.NoError(t, headState.SetGenesisValidatorRoot(params.BeaconConfig().ZeroHash[:]))
+	require.NoError(t, headState.SetGenesisValidatorsRoot(params.BeaconConfig().ZeroHash[:]))
 	require.NoError(t, beaconDB.SaveState(ctx, headState, genesisRoot))
 	require.NoError(t, beaconDB.SaveState(ctx, headState, finalizedRoot))
 	require.NoError(t, beaconDB.SaveState(ctx, headState, headRoot))
 	require.NoError(t, beaconDB.SaveHeadBlockRoot(ctx, headRoot))
 	require.NoError(t, beaconDB.SaveFinalizedCheckpoint(ctx, &ethpb.Checkpoint{
-		Epoch: core.SlotToEpoch(finalizedBlock.Block.Slot),
+		Epoch: slots.ToEpoch(finalizedBlock.Block.Slot),
 		Root:  finalizedRoot[:],
 	}))

-	c := &Service{cfg: &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)}}
-
-	require.NoError(t, c.initializeChainInfo(ctx))
+	attSrv, err := attestations.NewService(ctx, &attestations.Config{})
+	require.NoError(t, err)
+	c, err := NewService(ctx, WithDatabase(beaconDB), WithStateGen(stategen.New(beaconDB)), WithAttestationService(attSrv), WithStateNotifier(&mock.MockStateNotifier{}), WithFinalizedStateAtStartUp(headState))
+	require.NoError(t, err)
+	require.NoError(t, c.startFromSavedState(headState))
 	s, err := c.HeadState(ctx)
 	require.NoError(t, err)
 	assert.DeepSSZEqual(t, headState.InnerStateUnsafe(), s.InnerStateUnsafe(), "Head state incorrect")
-	assert.Equal(t, genesisRoot, c.genesisRoot, "Genesis block root incorrect")
+	assert.Equal(t, genesisRoot, c.originBlockRoot, "Genesis block root incorrect")
 	// Since head sync is not triggered, chain is initialized to the last finalization checkpoint.
 	assert.DeepEqual(t, finalizedBlock, c.head.block.Proto())
 	assert.LogsContain(t, hook, "resetting head from the checkpoint ('--head-sync' flag is ignored)")
 	assert.LogsDoNotContain(t, hook, "Regenerating state from the last checkpoint at slot")

 	// Set head slot far beyond the finalization point, head sync should be triggered.
-	headBlock = testutil.NewBeaconBlock()
+	headBlock = util.NewBeaconBlock()
 	headBlock.Block.Slot = finalizedSlot + params.BeaconConfig().SlotsPerEpoch*headSyncMinEpochsAfterCheckpoint
 	headBlock.Block.ParentRoot = finalizedRoot[:]
 	headRoot, err = headBlock.Block.HashTreeRoot()
@@ -402,11 +414,11 @@ func TestChainService_InitializeChainInfo_HeadSync(t *testing.T) {
 	require.NoError(t, beaconDB.SaveHeadBlockRoot(ctx, headRoot))

 	hook.Reset()
-	require.NoError(t, c.initializeChainInfo(ctx))
+	require.NoError(t, c.initializeHeadFromDB(ctx))
 	s, err = c.HeadState(ctx)
 	require.NoError(t, err)
 	assert.DeepSSZEqual(t, headState.InnerStateUnsafe(), s.InnerStateUnsafe(), "Head state incorrect")
-	assert.Equal(t, genesisRoot, c.genesisRoot, "Genesis block root incorrect")
+	assert.Equal(t, genesisRoot, c.originBlockRoot, "Genesis block root incorrect")
 	// Head slot is far beyond the latest finalized checkpoint, head sync is triggered.
 	assert.DeepEqual(t, headBlock, c.head.block.Proto())
 	assert.LogsContain(t, hook, "Regenerating state from the last checkpoint at slot 225")
@@ -417,13 +429,13 @@ func TestChainService_SaveHeadNoDB(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)
 	ctx := context.Background()
 	s := &Service{
-		cfg: &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
+		cfg: &config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
 	}
-	blk := testutil.NewBeaconBlock()
+	blk := util.NewBeaconBlock()
 	blk.Block.Slot = 1
 	r, err := blk.HashTreeRoot()
 	require.NoError(t, err)
-	newState, err := testutil.NewBeaconState()
+	newState, err := util.NewBeaconState()
 	require.NoError(t, err)
 	require.NoError(t, s.cfg.StateGen.SaveState(ctx, r, newState))
 	require.NoError(t, s.saveHeadNoDB(ctx, wrapper.WrappedPhase0SignedBeaconBlock(blk), r, newState))
@@ -435,19 +447,39 @@ func TestChainService_SaveHeadNoDB(t *testing.T) {
 	}
 }

-func TestHasBlock_ForkChoiceAndDB(t *testing.T) {
+func TestHasBlock_ForkChoiceAndDB_ProtoArray(t *testing.T) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg:              &Config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{}), BeaconDB: beaconDB},
-		finalizedCheckpt: &ethpb.Checkpoint{Root: make([]byte, 32)},
+		cfg:   &config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{}), BeaconDB: beaconDB},
+		store: &store.Store{},
 	}
-	block := testutil.NewBeaconBlock()
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 0, Root: params.BeaconConfig().ZeroHash[:]})
+	block := util.NewBeaconBlock()
 	r, err := block.Block.HashTreeRoot()
 	require.NoError(t, err)
-	beaconState, err := testutil.NewBeaconState()
+	beaconState, err := util.NewBeaconState()
 	require.NoError(t, err)
-	require.NoError(t, s.insertBlockAndAttestationsToForkChoiceStore(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block).Block(), r, beaconState))
+	require.NoError(t, s.insertBlockAndAttestationsToForkChoiceStore(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block).Block(), r, beaconState, false))
+
+	assert.Equal(t, false, s.hasBlock(ctx, [32]byte{}), "Should not have block")
+	assert.Equal(t, true, s.hasBlock(ctx, r), "Should have block")
+}
+
+func TestHasBlock_ForkChoiceAndDB_DoublyLinkedTree(t *testing.T) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(t)
+	s := &Service{
+		cfg:   &config{ForkChoiceStore: doublylinkedtree.New(0, 0), BeaconDB: beaconDB},
+		store: &store.Store{},
+	}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 0, Root: params.BeaconConfig().ZeroHash[:]})
+	block := util.NewBeaconBlock()
+	r, err := block.Block.HashTreeRoot()
+	require.NoError(t, err)
+	beaconState, err := util.NewBeaconState()
+	require.NoError(t, err)
+	require.NoError(t, s.insertBlockAndAttestationsToForkChoiceStore(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block).Block(), r, beaconState, false))

 	assert.Equal(t, false, s.hasBlock(ctx, [32]byte{}), "Should not have block")
 	assert.Equal(t, true, s.hasBlock(ctx, r), "Should have block")
@@ -457,12 +489,12 @@ func TestServiceStop_SaveCachedBlocks(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	beaconDB := testDB.SetupDB(t)
 	s := &Service{
-		cfg:            &Config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
+		cfg:            &config{BeaconDB: beaconDB, StateGen: stategen.New(beaconDB)},
 		ctx:            ctx,
 		cancel:         cancel,
 		initSyncBlocks: make(map[[32]byte]block.SignedBeaconBlock),
 	}
-	block := testutil.NewBeaconBlock()
+	block := util.NewBeaconBlock()
 	r, err := block.Block.HashTreeRoot()
 	require.NoError(t, err)
 	s.saveInitSyncBlock(r, wrapper.WrappedPhase0SignedBeaconBlock(block))
@@ -476,7 +508,7 @@ func TestProcessChainStartTime_ReceivedFeed(t *testing.T) {
 	stateChannel := make(chan *feed.Event, 1)
 	stateSub := service.cfg.StateNotifier.StateFeed().Subscribe(stateChannel)
 	defer stateSub.Unsubscribe()
-	service.processChainStartTime(context.Background(), time.Now())
+	service.onPowchainStart(context.Background(), time.Now())

 	stateEvent := <-stateChannel
 	require.Equal(t, int(stateEvent.Type), statefeed.Initialized)
@@ -488,9 +520,9 @@ func BenchmarkHasBlockDB(b *testing.B) {
 	beaconDB := testDB.SetupDB(b)
 	ctx := context.Background()
 	s := &Service{
-		cfg: &Config{BeaconDB: beaconDB},
+		cfg: &config{BeaconDB: beaconDB},
 	}
-	block := testutil.NewBeaconBlock()
+	block := util.NewBeaconBlock()
 	require.NoError(b, s.cfg.BeaconDB.SaveBlock(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block)))
 	r, err := block.Block.HashTreeRoot()
 	require.NoError(b, err)
@@ -501,20 +533,42 @@ func BenchmarkHasBlockDB(b *testing.B) {
 	}
 }

-func BenchmarkHasBlockForkChoiceStore(b *testing.B) {
+func BenchmarkHasBlockForkChoiceStore_ProtoArray(b *testing.B) {
 	ctx := context.Background()
 	beaconDB := testDB.SetupDB(b)
 	s := &Service{
-		cfg:              &Config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{}), BeaconDB: beaconDB},
-		finalizedCheckpt: &ethpb.Checkpoint{Root: make([]byte, 32)},
+		cfg:   &config{ForkChoiceStore: protoarray.New(0, 0, [32]byte{}), BeaconDB: beaconDB},
+		store: &store.Store{},
 	}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 0, Root: params.BeaconConfig().ZeroHash[:]})
 	block := &ethpb.SignedBeaconBlock{Block: &ethpb.BeaconBlock{Body: &ethpb.BeaconBlockBody{}}}
 	r, err := block.Block.HashTreeRoot()
 	require.NoError(b, err)
 	bs := &ethpb.BeaconState{FinalizedCheckpoint: &ethpb.Checkpoint{Root: make([]byte, 32)}, CurrentJustifiedCheckpoint: &ethpb.Checkpoint{Root: make([]byte, 32)}}
 	beaconState, err := v1.InitializeFromProto(bs)
 	require.NoError(b, err)
-	require.NoError(b, s.insertBlockAndAttestationsToForkChoiceStore(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block).Block(), r, beaconState))
+	require.NoError(b, s.insertBlockAndAttestationsToForkChoiceStore(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block).Block(), r, beaconState, false))
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		require.Equal(b, true, s.cfg.ForkChoiceStore.HasNode(r), "Block is not in fork choice store")
+	}
+}
+func BenchmarkHasBlockForkChoiceStore_DoublyLinkedTree(b *testing.B) {
+	ctx := context.Background()
+	beaconDB := testDB.SetupDB(b)
+	s := &Service{
+		cfg:   &config{ForkChoiceStore: doublylinkedtree.New(0, 0), BeaconDB: beaconDB},
+		store: &store.Store{},
+	}
+	s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: 0, Root: params.BeaconConfig().ZeroHash[:]})
+	block := &ethpb.SignedBeaconBlock{Block: &ethpb.BeaconBlock{Body: &ethpb.BeaconBlockBody{}}}
+	r, err := block.Block.HashTreeRoot()
+	require.NoError(b, err)
+	bs := &ethpb.BeaconState{FinalizedCheckpoint: &ethpb.Checkpoint{Root: make([]byte, 32)}, CurrentJustifiedCheckpoint: &ethpb.Checkpoint{Root: make([]byte, 32)}}
+	beaconState, err := v1.InitializeFromProto(bs)
+	require.NoError(b, err)
+	require.NoError(b, s.insertBlockAndAttestationsToForkChoiceStore(ctx, wrapper.WrappedPhase0SignedBeaconBlock(block).Block(), r, beaconState, false))

 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
--- a/beacon-chain/blockchain/state_balance_cache.go
+++ b/beacon-chain/blockchain/state_balance_cache.go
@@ -0,0 +1,83 @@
+package blockchain
+
+import (
+	"context"
+	"errors"
+	"sync"
+
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
+	"github.com/prysmaticlabs/prysm/beacon-chain/core/time"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state/stategen"
+)
+
+var errNilStateFromStategen = errors.New("justified state can't be nil")
+
+type stateBalanceCache struct {
+	sync.Mutex
+	balances []uint64
+	root     [32]byte
+	stateGen stateByRooter
+}
+
+type stateByRooter interface {
+	StateByRoot(context.Context, [32]byte) (state.BeaconState, error)
+}
+
+// newStateBalanceCache exists to remind us that stateBalanceCache needs a stagegen
+// to avoid nil pointer bugs when updating the cache in the read path (get())
+func newStateBalanceCache(sg *stategen.State) (*stateBalanceCache, error) {
+	if sg == nil {
+		return nil, errors.New("can't initialize state balance cache without stategen")
+	}
+	return &stateBalanceCache{stateGen: sg}, nil
+}
+
+// update is called by get() when the requested root doesn't match
+// the previously read value. This cache assumes we only want to cache one
+// set of balances for a single root (the current justified root).
+//
+// warning: this is not thread-safe on its own, relies on get() for locking
+func (c *stateBalanceCache) update(ctx context.Context, justifiedRoot [32]byte) ([]uint64, error) {
+	stateBalanceCacheMiss.Inc()
+	justifiedState, err := c.stateGen.StateByRoot(ctx, justifiedRoot)
+	if err != nil {
+		return nil, err
+	}
+	if justifiedState == nil || justifiedState.IsNil() {
+		return nil, errNilStateFromStategen
+	}
+	epoch := time.CurrentEpoch(justifiedState)
+
+	justifiedBalances := make([]uint64, justifiedState.NumValidators())
+	var balanceAccumulator = func(idx int, val state.ReadOnlyValidator) error {
+		if helpers.IsActiveValidatorUsingTrie(val, epoch) {
+			justifiedBalances[idx] = val.EffectiveBalance()
+		} else {
+			justifiedBalances[idx] = 0
+		}
+		return nil
+	}
+	if err := justifiedState.ReadFromEveryValidator(balanceAccumulator); err != nil {
+		return nil, err
+	}
+
+	c.balances = justifiedBalances
+	c.root = justifiedRoot
+	return c.balances, nil
+}
+
+// getBalances takes an explicit justifiedRoot so it can invalidate the singleton cache key
+// when the justified root changes, and takes a context so that the long-running stategen
+// read path can connect to the upstream cancellation/timeout chain.
+func (c *stateBalanceCache) get(ctx context.Context, justifiedRoot [32]byte) ([]uint64, error) {
+	c.Lock()
+	defer c.Unlock()
+
+	if justifiedRoot != [32]byte{} && justifiedRoot == c.root {
+		stateBalanceCacheHit.Inc()
+		return c.balances, nil
+	}
+
+	return c.update(ctx, justifiedRoot)
+}
--- a/beacon-chain/blockchain/state_balance_cache_test.go
+++ b/beacon-chain/blockchain/state_balance_cache_test.go
@@ -0,0 +1,236 @@
+package blockchain
+
+import (
+	"context"
+	"encoding/binary"
+	"errors"
+	"testing"
+
+	types "github.com/prysmaticlabs/eth2-types"
+	"github.com/prysmaticlabs/prysm/beacon-chain/state"
+	v2 "github.com/prysmaticlabs/prysm/beacon-chain/state/v2"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/time/slots"
+)
+
+type mockStateByRoot struct {
+	state state.BeaconState
+	err   error
+}
+
+func (m *mockStateByRoot) StateByRoot(context.Context, [32]byte) (state.BeaconState, error) {
+	return m.state, m.err
+}
+
+type testStateOpt func(*ethpb.BeaconStateAltair)
+
+func testStateWithValidators(v []*ethpb.Validator) testStateOpt {
+	return func(a *ethpb.BeaconStateAltair) {
+		a.Validators = v
+	}
+}
+
+func testStateWithSlot(slot types.Slot) testStateOpt {
+	return func(a *ethpb.BeaconStateAltair) {
+		a.Slot = slot
+	}
+}
+
+func testStateFixture(opts ...testStateOpt) state.BeaconState {
+	a := &ethpb.BeaconStateAltair{}
+	for _, o := range opts {
+		o(a)
+	}
+	s, _ := v2.InitializeFromProtoUnsafe(a)
+	return s
+}
+
+func generateTestValidators(count int, opts ...func(*ethpb.Validator)) []*ethpb.Validator {
+	vs := make([]*ethpb.Validator, count)
+	var i uint32 = 0
+	for ; i < uint32(count); i++ {
+		pk := make([]byte, 48)
+		binary.LittleEndian.PutUint32(pk, i)
+		v := &ethpb.Validator{PublicKey: pk}
+		for _, o := range opts {
+			o(v)
+		}
+		vs[i] = v
+	}
+	return vs
+}
+
+func oddValidatorsExpired(currentSlot types.Slot) func(*ethpb.Validator) {
+	return func(v *ethpb.Validator) {
+		pki := binary.LittleEndian.Uint64(v.PublicKey)
+		if pki%2 == 0 {
+			v.ExitEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) + 1)
+		} else {
+			v.ExitEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) - 1)
+		}
+	}
+}
+
+func oddValidatorsQueued(currentSlot types.Slot) func(*ethpb.Validator) {
+	return func(v *ethpb.Validator) {
+		v.ExitEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) + 1)
+		pki := binary.LittleEndian.Uint64(v.PublicKey)
+		if pki%2 == 0 {
+			v.ActivationEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) - 1)
+		} else {
+			v.ActivationEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) + 1)
+		}
+	}
+}
+
+func allValidatorsValid(currentSlot types.Slot) func(*ethpb.Validator) {
+	return func(v *ethpb.Validator) {
+		v.ActivationEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) - 1)
+		v.ExitEpoch = types.Epoch(int(slots.ToEpoch(currentSlot)) + 1)
+	}
+}
+
+func balanceIsKeyTimes2(v *ethpb.Validator) {
+	pki := binary.LittleEndian.Uint64(v.PublicKey)
+	v.EffectiveBalance = uint64(pki) * 2
+}
+
+func testHalfExpiredValidators() ([]*ethpb.Validator, []uint64) {
+	balances := []uint64{0, 0, 4, 0, 8, 0, 12, 0, 16, 0}
+	return generateTestValidators(10,
+		oddValidatorsExpired(types.Slot(99)),
+		balanceIsKeyTimes2), balances
+}
+
+func testHalfQueuedValidators() ([]*ethpb.Validator, []uint64) {
+	balances := []uint64{0, 0, 4, 0, 8, 0, 12, 0, 16, 0}
+	return generateTestValidators(10,
+		oddValidatorsQueued(types.Slot(99)),
+		balanceIsKeyTimes2), balances
+}
+
+func testAllValidValidators() ([]*ethpb.Validator, []uint64) {
+	balances := []uint64{0, 2, 4, 6, 8, 10, 12, 14, 16, 18}
+	return generateTestValidators(10,
+		allValidatorsValid(types.Slot(99)),
+		balanceIsKeyTimes2), balances
+}
+
+func TestStateBalanceCache(t *testing.T) {
+	type sbcTestCase struct {
+		err      error
+		root     [32]byte
+		sbc      *stateBalanceCache
+		balances []uint64
+		name     string
+	}
+	sentinelCacheMiss := errors.New("Cache missed, as expected!")
+	sentinelBalances := []uint64{1, 2, 3, 4, 5}
+	halfExpiredValidators, halfExpiredBalances := testHalfExpiredValidators()
+	halfQueuedValidators, halfQueuedBalances := testHalfQueuedValidators()
+	allValidValidators, allValidBalances := testAllValidValidators()
+	cases := []sbcTestCase{
+		{
+			root:     bytesutil.ToBytes32([]byte{'A'}),
+			balances: sentinelBalances,
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{
+					err: sentinelCacheMiss,
+				},
+				root:     bytesutil.ToBytes32([]byte{'A'}),
+				balances: sentinelBalances,
+			},
+			name: "cache hit",
+		},
+		// this works by using a staterooter that returns a known error
+		// so really we're testing the miss by making sure stategen got called
+		// this also tells us stategen errors are propagated
+		{
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{
+					err: sentinelCacheMiss,
+				},
+				root: bytesutil.ToBytes32([]byte{'B'}),
+			},
+			err:  sentinelCacheMiss,
+			root: bytesutil.ToBytes32([]byte{'A'}),
+			name: "cache miss",
+		},
+		{
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{},
+				root:     bytesutil.ToBytes32([]byte{'B'}),
+			},
+			err:  errNilStateFromStategen,
+			root: bytesutil.ToBytes32([]byte{'A'}),
+			name: "error for nil state upon cache miss",
+		},
+		{
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{
+					state: testStateFixture(
+						testStateWithSlot(99),
+						testStateWithValidators(halfExpiredValidators)),
+				},
+			},
+			balances: halfExpiredBalances,
+			root:     bytesutil.ToBytes32([]byte{'A'}),
+			name:     "test filtering by exit epoch",
+		},
+		{
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{
+					state: testStateFixture(
+						testStateWithSlot(99),
+						testStateWithValidators(halfQueuedValidators)),
+				},
+			},
+			balances: halfQueuedBalances,
+			root:     bytesutil.ToBytes32([]byte{'A'}),
+			name:     "test filtering by activation epoch",
+		},
+		{
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{
+					state: testStateFixture(
+						testStateWithSlot(99),
+						testStateWithValidators(allValidValidators)),
+				},
+			},
+			balances: allValidBalances,
+			root:     bytesutil.ToBytes32([]byte{'A'}),
+			name:     "happy path",
+		},
+		{
+			sbc: &stateBalanceCache{
+				stateGen: &mockStateByRooter{
+					state: testStateFixture(
+						testStateWithSlot(99),
+						testStateWithValidators(allValidValidators)),
+				},
+			},
+			balances: allValidBalances,
+			root:     [32]byte{},
+			name:     "zero root",
+		},
+	}
+	ctx := context.Background()
+	for _, c := range cases {
+		t.Run(c.name, func(t *testing.T) {
+			cache := c.sbc
+			cacheRootStart := cache.root
+			b, err := cache.get(ctx, c.root)
+			require.ErrorIs(t, err, c.err)
+			require.DeepEqual(t, c.balances, b)
+			if c.err != nil {
+				// if there was an error somewhere, the root should not have changed (unless it already matched)
+				require.Equal(t, cacheRootStart, cache.root)
+			} else {
+				// when successful, the cache should always end with a root matching the request
+				require.Equal(t, c.root, cache.root)
+			}
+		})
+	}
+}
--- a/beacon-chain/blockchain/store/BUILD.bazel
+++ b/beacon-chain/blockchain/store/BUILD.bazel
@@ -0,0 +1,27 @@
+load("@prysm//tools/go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "doc.go",
+        "new.go",
+        "setter_getter.go",
+        "type.go",
+    ],
+    importpath = "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/store",
+    visibility = ["//beacon-chain:__subpackages__"],
+    deps = ["//proto/prysm/v1alpha1:go_default_library"],
+)
+
+go_test(
+    name = "go_default_test",
+    srcs = [
+        "new_test.go",
+        "setter_getter_test.go",
+    ],
+    embed = [":go_default_library"],
+    deps = [
+        "//proto/prysm/v1alpha1:go_default_library",
+        "//testing/require:go_default_library",
+    ],
+)
--- a/beacon-chain/blockchain/store/doc.go
+++ b/beacon-chain/blockchain/store/doc.go
@@ -0,0 +1,4 @@
+// Package store implements the store object defined in the phase0 fork choice spec.
+// It serves as a helpful middleware layer in between blockchain pkg and fork choice protoarray pkg.
+// All the getters and setters are concurrent thread safe
+package store
--- a/beacon-chain/blockchain/store/new.go
+++ b/beacon-chain/blockchain/store/new.go
@@ -0,0 +1,15 @@
+package store
+
+import (
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+)
+
+func New(justifiedCheckpt *ethpb.Checkpoint, finalizedCheckpt *ethpb.Checkpoint) *Store {
+	return &Store{
+		justifiedCheckpt:     justifiedCheckpt,
+		prevJustifiedCheckpt: justifiedCheckpt,
+		bestJustifiedCheckpt: justifiedCheckpt,
+		finalizedCheckpt:     finalizedCheckpt,
+		prevFinalizedCheckpt: finalizedCheckpt,
+	}
+}
--- a/beacon-chain/blockchain/store/new_test.go
+++ b/beacon-chain/blockchain/store/new_test.go
@@ -0,0 +1,25 @@
+package store
+
+import (
+	"testing"
+
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func TestNew(t *testing.T) {
+	j := &ethpb.Checkpoint{
+		Epoch: 0,
+		Root:  []byte("hi"),
+	}
+	f := &ethpb.Checkpoint{
+		Epoch: 0,
+		Root:  []byte("hello"),
+	}
+	s := New(j, f)
+	require.DeepSSZEqual(t, s.JustifiedCheckpt(), j)
+	require.DeepSSZEqual(t, s.BestJustifiedCheckpt(), j)
+	require.DeepSSZEqual(t, s.PrevJustifiedCheckpt(), j)
+	require.DeepSSZEqual(t, s.FinalizedCheckpt(), f)
+	require.DeepSSZEqual(t, s.PrevFinalizedCheckpt(), f)
+}
--- a/beacon-chain/blockchain/store/setter_getter.go
+++ b/beacon-chain/blockchain/store/setter_getter.go
@@ -0,0 +1,73 @@
+package store
+
+import ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+
+// PrevJustifiedCheckpt returns the previous justified checkpoint in the Store.
+func (s *Store) PrevJustifiedCheckpt() *ethpb.Checkpoint {
+	s.RLock()
+	defer s.RUnlock()
+	return s.prevJustifiedCheckpt
+}
+
+// BestJustifiedCheckpt returns the best justified checkpoint in the Store.
+func (s *Store) BestJustifiedCheckpt() *ethpb.Checkpoint {
+	s.RLock()
+	defer s.RUnlock()
+	return s.bestJustifiedCheckpt
+}
+
+// JustifiedCheckpt returns the justified checkpoint in the Store.
+func (s *Store) JustifiedCheckpt() *ethpb.Checkpoint {
+	s.RLock()
+	defer s.RUnlock()
+	return s.justifiedCheckpt
+}
+
+// PrevFinalizedCheckpt returns the previous finalized checkpoint in the Store.
+func (s *Store) PrevFinalizedCheckpt() *ethpb.Checkpoint {
+	s.RLock()
+	defer s.RUnlock()
+	return s.prevFinalizedCheckpt
+}
+
+// FinalizedCheckpt returns the finalized checkpoint in the Store.
+func (s *Store) FinalizedCheckpt() *ethpb.Checkpoint {
+	s.RLock()
+	defer s.RUnlock()
+	return s.finalizedCheckpt
+}
+
+// SetPrevJustifiedCheckpt sets the previous justified checkpoint in the Store.
+func (s *Store) SetPrevJustifiedCheckpt(cp *ethpb.Checkpoint) {
+	s.Lock()
+	defer s.Unlock()
+	s.prevJustifiedCheckpt = cp
+}
+
+// SetBestJustifiedCheckpt sets the best justified checkpoint in the Store.
+func (s *Store) SetBestJustifiedCheckpt(cp *ethpb.Checkpoint) {
+	s.Lock()
+	defer s.Unlock()
+	s.bestJustifiedCheckpt = cp
+}
+
+// SetJustifiedCheckpt sets the justified checkpoint in the Store.
+func (s *Store) SetJustifiedCheckpt(cp *ethpb.Checkpoint) {
+	s.Lock()
+	defer s.Unlock()
+	s.justifiedCheckpt = cp
+}
+
+// SetFinalizedCheckpt sets the finalized checkpoint in the Store.
+func (s *Store) SetFinalizedCheckpt(cp *ethpb.Checkpoint) {
+	s.Lock()
+	defer s.Unlock()
+	s.finalizedCheckpt = cp
+}
+
+// SetPrevFinalizedCheckpt sets the previous finalized checkpoint in the Store.
+func (s *Store) SetPrevFinalizedCheckpt(cp *ethpb.Checkpoint) {
+	s.Lock()
+	defer s.Unlock()
+	s.prevFinalizedCheckpt = cp
+}
--- a/beacon-chain/blockchain/store/setter_getter_test.go
+++ b/beacon-chain/blockchain/store/setter_getter_test.go
@@ -0,0 +1,53 @@
+package store
+
+import (
+	"testing"
+
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/testing/require"
+)
+
+func Test_store_PrevJustifiedCheckpt(t *testing.T) {
+	s := &Store{}
+	var cp *ethpb.Checkpoint
+	require.Equal(t, cp, s.PrevJustifiedCheckpt())
+	cp = &ethpb.Checkpoint{Epoch: 1, Root: []byte{'a'}}
+	s.SetPrevJustifiedCheckpt(cp)
+	require.Equal(t, cp, s.PrevJustifiedCheckpt())
+}
+
+func Test_store_BestJustifiedCheckpt(t *testing.T) {
+	s := &Store{}
+	var cp *ethpb.Checkpoint
+	require.Equal(t, cp, s.BestJustifiedCheckpt())
+	cp = &ethpb.Checkpoint{Epoch: 1, Root: []byte{'a'}}
+	s.SetBestJustifiedCheckpt(cp)
+	require.Equal(t, cp, s.BestJustifiedCheckpt())
+}
+
+func Test_store_JustifiedCheckpt(t *testing.T) {
+	s := &Store{}
+	var cp *ethpb.Checkpoint
+	require.Equal(t, cp, s.JustifiedCheckpt())
+	cp = &ethpb.Checkpoint{Epoch: 1, Root: []byte{'a'}}
+	s.SetJustifiedCheckpt(cp)
+	require.Equal(t, cp, s.JustifiedCheckpt())
+}
+
+func Test_store_FinalizedCheckpt(t *testing.T) {
+	s := &Store{}
+	var cp *ethpb.Checkpoint
+	require.Equal(t, cp, s.FinalizedCheckpt())
+	cp = &ethpb.Checkpoint{Epoch: 1, Root: []byte{'a'}}
+	s.SetFinalizedCheckpt(cp)
+	require.Equal(t, cp, s.FinalizedCheckpt())
+}
+
+func Test_store_PrevFinalizedCheckpt(t *testing.T) {
+	s := &Store{}
+	var cp *ethpb.Checkpoint
+	require.Equal(t, cp, s.PrevFinalizedCheckpt())
+	cp = &ethpb.Checkpoint{Epoch: 1, Root: []byte{'a'}}
+	s.SetPrevFinalizedCheckpt(cp)
+	require.Equal(t, cp, s.PrevFinalizedCheckpt())
+}
--- a/beacon-chain/blockchain/store/type.go
+++ b/beacon-chain/blockchain/store/type.go
@@ -0,0 +1,28 @@
+package store
+
+import (
+	"sync"
+
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+)
+
+// Store is defined in the fork choice consensus spec for tracking current time and various versions of checkpoints.
+//
+// Spec code:
+// class Store(object):
+//    time: uint64
+//    genesis_time: uint64
+//    justified_checkpoint: Checkpoint
+//    finalized_checkpoint: Checkpoint
+//    best_justified_checkpoint: Checkpoint
+//    proposerBoostRoot: Root
+type Store struct {
+	justifiedCheckpt     *ethpb.Checkpoint
+	finalizedCheckpt     *ethpb.Checkpoint
+	bestJustifiedCheckpt *ethpb.Checkpoint
+	sync.RWMutex
+	// These are not part of the consensus spec, but we do use them to return gRPC API requests.
+	// TODO(10094): Consider removing in v3.
+	prevFinalizedCheckpt *ethpb.Checkpoint
+	prevJustifiedCheckpt *ethpb.Checkpoint
+}
--- a/beacon-chain/blockchain/testing/BUILD.bazel
+++ b/beacon-chain/blockchain/testing/BUILD.bazel
@@ -7,7 +7,7 @@ go_library(
    importpath = "github.com/prysmaticlabs/prysm/beacon-chain/blockchain/testing",
    visibility = [
        "//beacon-chain:__subpackages__",
-        "//testing/fuzz:__pkg__",
+        "//testing:__subpackages__",
    ],
    deps = [
        "//async/event:go_default_library",
@@ -18,13 +18,13 @@ go_library(
        "//beacon-chain/core/feed/state:go_default_library",
        "//beacon-chain/core/helpers:go_default_library",
        "//beacon-chain/db:go_default_library",
-        "//beacon-chain/forkchoice/protoarray:go_default_library",
+        "//beacon-chain/forkchoice:go_default_library",
        "//beacon-chain/state:go_default_library",
-        "//beacon-chain/state/v1:go_default_library",
+        "//config/fieldparams:go_default_library",
+        "//config/params:go_default_library",
+        "//encoding/bytesutil:go_default_library",
        "//proto/prysm/v1alpha1:go_default_library",
        "//proto/prysm/v1alpha1/block:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "//shared/params:go_default_library",
        "@com_github_pkg_errors//:go_default_library",
        "@com_github_prysmaticlabs_eth2_types//:go_default_library",
        "@com_github_sirupsen_logrus//:go_default_library",
--- a/beacon-chain/blockchain/testing/mock.go
+++ b/beacon-chain/blockchain/testing/mock.go
@@ -18,45 +18,54 @@ import (
 	statefeed "github.com/prysmaticlabs/prysm/beacon-chain/core/feed/state"
 	"github.com/prysmaticlabs/prysm/beacon-chain/core/helpers"
 	"github.com/prysmaticlabs/prysm/beacon-chain/db"
-	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice/protoarray"
+	"github.com/prysmaticlabs/prysm/beacon-chain/forkchoice"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
-	v1 "github.com/prysmaticlabs/prysm/beacon-chain/state/v1"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/block"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
 	"github.com/sirupsen/logrus"
 )

+var ErrNilState = errors.New("nil state")
+
 // ChainService defines the mock interface for testing
 type ChainService struct {
-	State                       state.BeaconState
-	Root                        []byte
-	Block                       block.SignedBeaconBlock
+	Optimistic                  bool
+	ValidAttestation            bool
+	ValidatorsRoot              [32]byte
+	PublicKey                   [fieldparams.BLSPubkeyLength]byte
 	FinalizedCheckPoint         *ethpb.Checkpoint
 	CurrentJustifiedCheckPoint  *ethpb.Checkpoint
 	PreviousJustifiedCheckPoint *ethpb.Checkpoint
-	BlocksReceived              []block.SignedBeaconBlock
+	Slot                        *types.Slot // Pointer because 0 is a useful value, so checking against it can be incorrect.
 	Balance                     *precompute.Balance
-	Genesis                     time.Time
-	ValidatorsRoot              [32]byte
 	CanonicalRoots              map[[32]byte]bool
 	Fork                        *ethpb.Fork
 	ETH1Data                    *ethpb.Eth1Data
+	InitSyncBlockRoots          map[[32]byte]bool
 	DB                          db.Database
+	State                       state.BeaconState
+	Block                       block.SignedBeaconBlock
+	VerifyBlkDescendantErr      error
 	stateNotifier               statefeed.Notifier
+	BlocksReceived              []block.SignedBeaconBlock
+	SyncCommitteeIndices        []types.CommitteeIndex
 	blockNotifier               blockfeed.Notifier
 	opNotifier                  opfeed.Notifier
-	ValidAttestation            bool
-	ForkChoiceStore             *protoarray.Store
-	VerifyBlkDescendantErr      error
-	Slot                        *types.Slot // Pointer because 0 is a useful value, so checking against it can be incorrect.
-	SyncCommitteeIndices        []types.CommitteeIndex
+	Root                        []byte
 	SyncCommitteeDomain         []byte
 	SyncSelectionProofDomain    []byte
 	SyncContributionProofDomain []byte
-	PublicKey                   [48]byte
 	SyncCommitteePubkeys        [][]byte
+	Genesis                     time.Time
+	ForkChoiceStore             forkchoice.ForkChoicer
+}
+
+// ForkChoicer mocks the same method in the chain service
+func (s *ChainService) ForkChoicer() forkchoice.ForkChoicer {
+	return s.ForkChoiceStore
 }

 // StateNotifier mocks the same method in the chain service.
@@ -157,7 +166,7 @@ func (mon *MockOperationNotifier) OperationFeed() *event.Feed {
 // ReceiveBlockInitialSync mocks ReceiveBlockInitialSync method in chain service.
 func (s *ChainService) ReceiveBlockInitialSync(ctx context.Context, block block.SignedBeaconBlock, _ [32]byte) error {
 	if s.State == nil {
-		s.State = &v1.BeaconState{}
+		return ErrNilState
 	}
 	if !bytes.Equal(s.Root, block.Block().ParentRoot()) {
 		return errors.Errorf("wanted %#x but got %#x", s.Root, block.Block().ParentRoot())
@@ -184,7 +193,7 @@ func (s *ChainService) ReceiveBlockInitialSync(ctx context.Context, block block.
 // ReceiveBlockBatch processes blocks in batches from initial-sync.
 func (s *ChainService) ReceiveBlockBatch(ctx context.Context, blks []block.SignedBeaconBlock, _ [][32]byte) error {
 	if s.State == nil {
-		s.State = &v1.BeaconState{}
+		return ErrNilState
 	}
 	for _, block := range blks {
 		if !bytes.Equal(s.Root, block.Block().ParentRoot()) {
@@ -213,7 +222,7 @@ func (s *ChainService) ReceiveBlockBatch(ctx context.Context, blks []block.Signe
 // ReceiveBlock mocks ReceiveBlock method in chain service.
 func (s *ChainService) ReceiveBlock(ctx context.Context, block block.SignedBeaconBlock, _ [32]byte) error {
 	if s.State == nil {
-		s.State = &v1.BeaconState{}
+		return ErrNilState
 	}
 	if !bytes.Equal(s.Root, block.Block().ParentRoot()) {
 		return errors.Errorf("wanted %#x but got %#x", s.Root, block.Block().ParentRoot())
@@ -284,26 +293,26 @@ func (s *ChainService) PreviousJustifiedCheckpt() *ethpb.Checkpoint {
 }

 // ReceiveAttestation mocks ReceiveAttestation method in chain service.
-func (s *ChainService) ReceiveAttestation(_ context.Context, _ *ethpb.Attestation) error {
+func (_ *ChainService) ReceiveAttestation(_ context.Context, _ *ethpb.Attestation) error {
 	return nil
 }

 // ReceiveAttestationNoPubsub mocks ReceiveAttestationNoPubsub method in chain service.
-func (s *ChainService) ReceiveAttestationNoPubsub(context.Context, *ethpb.Attestation) error {
+func (_ *ChainService) ReceiveAttestationNoPubsub(context.Context, *ethpb.Attestation) error {
 	return nil
 }

-// AttestationPreState mocks AttestationPreState method in chain service.
-func (s *ChainService) AttestationPreState(_ context.Context, _ *ethpb.Attestation) (state.BeaconState, error) {
+// AttestationTargetState mocks AttestationTargetState method in chain service.
+func (s *ChainService) AttestationTargetState(_ context.Context, _ *ethpb.Checkpoint) (state.BeaconState, error) {
 	return s.State, nil
 }

 // HeadValidatorsIndices mocks the same method in the chain service.
-func (s *ChainService) HeadValidatorsIndices(_ context.Context, epoch types.Epoch) ([]types.ValidatorIndex, error) {
+func (s *ChainService) HeadValidatorsIndices(ctx context.Context, epoch types.Epoch) ([]types.ValidatorIndex, error) {
 	if s.State == nil {
 		return []types.ValidatorIndex{}, nil
 	}
-	return helpers.ActiveValidatorIndices(s.State, epoch)
+	return helpers.ActiveValidatorIndices(ctx, s.State, epoch)
 }

 // HeadSeed mocks the same method in the chain service.
@@ -316,18 +325,13 @@ func (s *ChainService) HeadETH1Data() *ethpb.Eth1Data {
 	return s.ETH1Data
 }

-// ProtoArrayStore mocks the same method in the chain service.
-func (s *ChainService) ProtoArrayStore() *protoarray.Store {
-	return s.ForkChoiceStore
-}
-
 // GenesisTime mocks the same method in the chain service.
 func (s *ChainService) GenesisTime() time.Time {
 	return s.Genesis
 }

-// GenesisValidatorRoot mocks the same method in the chain service.
-func (s *ChainService) GenesisValidatorRoot() [32]byte {
+// GenesisValidatorsRoot mocks the same method in the chain service.
+func (s *ChainService) GenesisValidatorsRoot() [32]byte {
 	return s.ValidatorsRoot
 }

@@ -360,12 +364,15 @@ func (s *ChainService) IsCanonical(_ context.Context, r [32]byte) (bool, error)
 }

 // HasInitSyncBlock mocks the same method in the chain service.
-func (s *ChainService) HasInitSyncBlock(_ [32]byte) bool {
-	return false
+func (s *ChainService) HasInitSyncBlock(rt [32]byte) bool {
+	if s.InitSyncBlockRoots == nil {
+		return false
+	}
+	return s.InitSyncBlockRoots[rt]
 }

-// HeadGenesisValidatorRoot mocks HeadGenesisValidatorRoot method in chain service.
-func (s *ChainService) HeadGenesisValidatorRoot() [32]byte {
+// HeadGenesisValidatorsRoot mocks HeadGenesisValidatorsRoot method in chain service.
+func (_ *ChainService) HeadGenesisValidatorsRoot() [32]byte {
 	return [32]byte{}
 }

@@ -375,7 +382,7 @@ func (s *ChainService) VerifyBlkDescendant(_ context.Context, _ [32]byte) error
 }

 // VerifyLmdFfgConsistency mocks VerifyLmdFfgConsistency and always returns nil.
-func (s *ChainService) VerifyLmdFfgConsistency(_ context.Context, a *ethpb.Attestation) error {
+func (_ *ChainService) VerifyLmdFfgConsistency(_ context.Context, a *ethpb.Attestation) error {
 	if !bytes.Equal(a.Data.BeaconBlockRoot, a.Data.Target.Root) {
 		return errors.New("LMD and FFG miss matched")
 	}
@@ -391,7 +398,7 @@ func (s *ChainService) VerifyFinalizedConsistency(_ context.Context, r []byte) e
 }

 // ChainHeads mocks ChainHeads and always return nil.
-func (s *ChainService) ChainHeads() ([][32]byte, []types.Slot) {
+func (_ *ChainService) ChainHeads() ([][32]byte, []types.Slot) {
 	return [][32]byte{
 			bytesutil.ToBytes32(bytesutil.PadTo([]byte("foo"), 32)),
 			bytesutil.ToBytes32(bytesutil.PadTo([]byte("bar"), 32)),
@@ -400,36 +407,46 @@ func (s *ChainService) ChainHeads() ([][32]byte, []types.Slot) {
 }

 // HeadPublicKeyToValidatorIndex mocks HeadPublicKeyToValidatorIndex and always return 0 and true.
-func (s *ChainService) HeadPublicKeyToValidatorIndex(ctx context.Context, pubKey [48]byte) (types.ValidatorIndex, bool) {
+func (_ *ChainService) HeadPublicKeyToValidatorIndex(_ [fieldparams.BLSPubkeyLength]byte) (types.ValidatorIndex, bool) {
 	return 0, true
 }

 // HeadValidatorIndexToPublicKey mocks HeadValidatorIndexToPublicKey and always return empty and nil.
-func (s *ChainService) HeadValidatorIndexToPublicKey(ctx context.Context, index types.ValidatorIndex) ([48]byte, error) {
+func (s *ChainService) HeadValidatorIndexToPublicKey(_ context.Context, _ types.ValidatorIndex) ([fieldparams.BLSPubkeyLength]byte, error) {
 	return s.PublicKey, nil
 }

 // HeadSyncCommitteeIndices mocks HeadSyncCommitteeIndices and always return `HeadNextSyncCommitteeIndices`.
-func (s *ChainService) HeadSyncCommitteeIndices(ctx context.Context, index types.ValidatorIndex, slot types.Slot) ([]types.CommitteeIndex, error) {
+func (s *ChainService) HeadSyncCommitteeIndices(_ context.Context, index types.ValidatorIndex, slot types.Slot) ([]types.CommitteeIndex, error) {
 	return s.SyncCommitteeIndices, nil
 }

 // HeadSyncCommitteePubKeys mocks HeadSyncCommitteePubKeys and always return empty nil.
-func (s *ChainService) HeadSyncCommitteePubKeys(ctx context.Context, slot types.Slot, committeeIndex types.CommitteeIndex) ([][]byte, error) {
+func (s *ChainService) HeadSyncCommitteePubKeys(_ context.Context, _ types.Slot, _ types.CommitteeIndex) ([][]byte, error) {
 	return s.SyncCommitteePubkeys, nil
 }

 // HeadSyncCommitteeDomain mocks HeadSyncCommitteeDomain and always return empty nil.
-func (s *ChainService) HeadSyncCommitteeDomain(ctx context.Context, slot types.Slot) ([]byte, error) {
+func (s *ChainService) HeadSyncCommitteeDomain(_ context.Context, _ types.Slot) ([]byte, error) {
 	return s.SyncCommitteeDomain, nil
 }

 // HeadSyncSelectionProofDomain mocks HeadSyncSelectionProofDomain and always return empty nil.
-func (s *ChainService) HeadSyncSelectionProofDomain(ctx context.Context, slot types.Slot) ([]byte, error) {
+func (s *ChainService) HeadSyncSelectionProofDomain(_ context.Context, _ types.Slot) ([]byte, error) {
 	return s.SyncSelectionProofDomain, nil
 }

 // HeadSyncContributionProofDomain mocks HeadSyncContributionProofDomain and always return empty nil.
-func (s *ChainService) HeadSyncContributionProofDomain(ctx context.Context, slot types.Slot) ([]byte, error) {
+func (s *ChainService) HeadSyncContributionProofDomain(_ context.Context, _ types.Slot) ([]byte, error) {
 	return s.SyncContributionProofDomain, nil
 }
+
+// IsOptimistic mocks the same method in the chain service.
+func (s *ChainService) IsOptimistic(_ context.Context) (bool, error) {
+	return s.Optimistic, nil
+}
+
+// IsOptimisticForRoot mocks the same method in the chain service.
+func (s *ChainService) IsOptimisticForRoot(_ context.Context, _ [32]byte) (bool, error) {
+	return s.Optimistic, nil
+}
--- a/beacon-chain/blockchain/weak_subjectivity_checks.go
+++ b/beacon-chain/blockchain/weak_subjectivity_checks.go
@@ -4,57 +4,94 @@ import (
 	"context"
 	"fmt"

-	"github.com/prysmaticlabs/prysm/beacon-chain/core"
+	"github.com/pkg/errors"
+	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/beacon-chain/db/filters"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
+	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
+	"github.com/prysmaticlabs/prysm/time/slots"
 )

-// VerifyWeakSubjectivityRoot verifies the weak subjectivity root in the service struct.
+var errWSBlockNotFound = errors.New("weak subjectivity root not found in db")
+var errWSBlockNotFoundInEpoch = errors.New("weak subjectivity root not found in db within epoch")
+
+type weakSubjectivityDB interface {
+	HasBlock(ctx context.Context, blockRoot [32]byte) bool
+	BlockRoots(ctx context.Context, f *filters.QueryFilter) ([][32]byte, error)
+}
+
+type WeakSubjectivityVerifier struct {
+	enabled  bool
+	verified bool
+	root     [32]byte
+	epoch    types.Epoch
+	slot     types.Slot
+	db       weakSubjectivityDB
+}
+
+// NewWeakSubjectivityVerifier validates a checkpoint, and if valid, uses it to initialize a weak subjectivity verifier
+func NewWeakSubjectivityVerifier(wsc *ethpb.Checkpoint, db weakSubjectivityDB) (*WeakSubjectivityVerifier, error) {
+	// TODO(7342): Weak subjectivity checks are currently optional. When we require the flag to be specified
+	// per 7342, a nil checkpoint, zero-root or zero-epoch should all fail validation
+	// and return an error instead of creating a WeakSubjectivityVerifier that permits any chain history.
+	if wsc == nil || len(wsc.Root) == 0 || wsc.Epoch == 0 {
+		return &WeakSubjectivityVerifier{
+			enabled: false,
+		}, nil
+	}
+	startSlot, err := slots.EpochStart(wsc.Epoch)
+	if err != nil {
+		return nil, err
+	}
+	return &WeakSubjectivityVerifier{
+		enabled:  true,
+		verified: false,
+		root:     bytesutil.ToBytes32(wsc.Root),
+		epoch:    wsc.Epoch,
+		db:       db,
+		slot:     startSlot,
+	}, nil
+}
+
+// VerifyWeakSubjectivity verifies the weak subjectivity root in the service struct.
 // Reference design: https://github.com/ethereum/consensus-specs/blob/master/specs/phase0/weak-subjectivity.md#weak-subjectivity-sync-procedure
-func (s *Service) VerifyWeakSubjectivityRoot(ctx context.Context) error {
-	// TODO(7342): Remove the following to fully use weak subjectivity in production.
-	if s.cfg.WeakSubjectivityCheckpt == nil || len(s.cfg.WeakSubjectivityCheckpt.Root) == 0 || s.cfg.WeakSubjectivityCheckpt.Epoch == 0 {
+func (v *WeakSubjectivityVerifier) VerifyWeakSubjectivity(ctx context.Context, finalizedEpoch types.Epoch) error {
+	if v.verified || !v.enabled {
 		return nil
 	}

-	// Do nothing if the weak subjectivity has previously been verified,
-	// or weak subjectivity epoch is higher than last finalized epoch.
-	if s.wsVerified {
-		return nil
-	}
-	if s.cfg.WeakSubjectivityCheckpt.Epoch > s.finalizedCheckpt.Epoch {
+	// Two conditions are described in the specs:
+	// IF epoch_number > store.finalized_checkpoint.epoch,
+	// then ASSERT during block sync that block with root block_root
+	// is in the sync path at epoch epoch_number. Emit descriptive critical error if this assert fails,
+	// then exit client process.
+	// we do not handle this case ^, because we can only blocks that have been processed / are currently
+	// in line for finalization, we don't have the ability to look ahead. so we only satisfy the following:
+	// IF epoch_number <= store.finalized_checkpoint.epoch,
+	// then ASSERT that the block in the canonical chain at epoch epoch_number has root block_root.
+	// Emit descriptive critical error if this assert fails, then exit client process.
+	if v.epoch > finalizedEpoch {
 		return nil
 	}
+	log.Infof("Performing weak subjectivity check for root %#x in epoch %d", v.root, v.epoch)

-	r := bytesutil.ToBytes32(s.cfg.WeakSubjectivityCheckpt.Root)
-	log.Infof("Performing weak subjectivity check for root %#x in epoch %d", r, s.cfg.WeakSubjectivityCheckpt.Epoch)
-	// Save initial sync cached blocks to DB.
-	if err := s.cfg.BeaconDB.SaveBlocks(ctx, s.getInitSyncBlocks()); err != nil {
-		return err
-	}
-	// A node should have the weak subjectivity block in the DB.
-	if !s.cfg.BeaconDB.HasBlock(ctx, r) {
-		return fmt.Errorf("node does not have root in DB: %#x", r)
-	}
-
-	startSlot, err := core.StartSlot(s.cfg.WeakSubjectivityCheckpt.Epoch)
-	if err != nil {
-		return err
+	if !v.db.HasBlock(ctx, v.root) {
+		return errors.Wrap(errWSBlockNotFound, fmt.Sprintf("missing root %#x", v.root))
 	}
+	filter := filters.NewFilter().SetStartSlot(v.slot).SetEndSlot(v.slot + params.BeaconConfig().SlotsPerEpoch)
 	// A node should have the weak subjectivity block corresponds to the correct epoch in the DB.
-	filter := filters.NewFilter().SetStartSlot(startSlot).SetEndSlot(startSlot + params.BeaconConfig().SlotsPerEpoch)
-	roots, err := s.cfg.BeaconDB.BlockRoots(ctx, filter)
+	roots, err := v.db.BlockRoots(ctx, filter)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "error while retrieving block roots to verify weak subjectivity")
 	}
 	for _, root := range roots {
-		if r == root {
+		if v.root == root {
 			log.Info("Weak subjectivity check has passed")
-			s.wsVerified = true
+			v.verified = true
 			return nil
 		}
 	}

-	return fmt.Errorf("node does not have root in db corresponding to epoch: %#x %d", r, s.cfg.WeakSubjectivityCheckpt.Epoch)
+	return errors.Wrap(errWSBlockNotFoundInEpoch, fmt.Sprintf("root=%#x, epoch=%d", v.root, v.epoch))
 }
--- a/beacon-chain/blockchain/weak_subjectivity_checks_test.go
+++ b/beacon-chain/blockchain/weak_subjectivity_checks_test.go
@@ -4,78 +4,80 @@ import (
 	"context"
 	"testing"

+	"github.com/pkg/errors"
 	types "github.com/prysmaticlabs/eth2-types"
+	"github.com/prysmaticlabs/prysm/beacon-chain/blockchain/store"
 	testDB "github.com/prysmaticlabs/prysm/beacon-chain/db/testing"
+	fieldparams "github.com/prysmaticlabs/prysm/config/fieldparams"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
 	"github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1/wrapper"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
+	"github.com/prysmaticlabs/prysm/testing/util"
 )

 func TestService_VerifyWeakSubjectivityRoot(t *testing.T) {
 	beaconDB := testDB.SetupDB(t)

-	b := testutil.NewBeaconBlock()
+	b := util.NewBeaconBlock()
 	b.Block.Slot = 32
 	require.NoError(t, beaconDB.SaveBlock(context.Background(), wrapper.WrappedPhase0SignedBeaconBlock(b)))
 	r, err := b.Block.HashTreeRoot()
 	require.NoError(t, err)
 	tests := []struct {
 		wsVerified     bool
-		wantErr        bool
+		wantErr        error
 		checkpt        *ethpb.Checkpoint
 		finalizedEpoch types.Epoch
-		errString      string
 		name           string
 	}{
 		{
-			name:    "nil root and epoch",
-			wantErr: false,
+			name: "nil root and epoch",
 		},
 		{
 			name:           "already verified",
 			checkpt:        &ethpb.Checkpoint{Epoch: 2},
 			finalizedEpoch: 2,
 			wsVerified:     true,
-			wantErr:        false,
 		},
 		{
 			name:           "not yet to verify, ws epoch higher than finalized epoch",
 			checkpt:        &ethpb.Checkpoint{Epoch: 2},
 			finalizedEpoch: 1,
-			wantErr:        false,
 		},
 		{
 			name:           "can't find the block in DB",
-			checkpt:        &ethpb.Checkpoint{Root: bytesutil.PadTo([]byte{'a'}, 32), Epoch: 1},
+			checkpt:        &ethpb.Checkpoint{Root: bytesutil.PadTo([]byte{'a'}, fieldparams.RootLength), Epoch: 1},
 			finalizedEpoch: 3,
-			wantErr:        true,
-			errString:      "node does not have root in DB",
+			wantErr:        errWSBlockNotFound,
 		},
 		{
 			name:           "can't find the block corresponds to ws epoch in DB",
 			checkpt:        &ethpb.Checkpoint{Root: r[:], Epoch: 2}, // Root belongs in epoch 1.
 			finalizedEpoch: 3,
-			wantErr:        true,
-			errString:      "node does not have root in db corresponding to epoch",
+			wantErr:        errWSBlockNotFoundInEpoch,
 		},
 		{
 			name:           "can verify and pass",
 			checkpt:        &ethpb.Checkpoint{Root: r[:], Epoch: 1},
 			finalizedEpoch: 3,
-			wantErr:        false,
 		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			wv, err := NewWeakSubjectivityVerifier(tt.checkpt, beaconDB)
+			require.NoError(t, err)
 			s := &Service{
-				cfg:              &Config{BeaconDB: beaconDB, WeakSubjectivityCheckpt: tt.checkpt},
-				wsVerified:       tt.wsVerified,
-				finalizedCheckpt: &ethpb.Checkpoint{Epoch: tt.finalizedEpoch},
+				cfg:        &config{BeaconDB: beaconDB, WeakSubjectivityCheckpt: tt.checkpt},
+				store:      &store.Store{},
+				wsVerifier: wv,
 			}
-			if err := s.VerifyWeakSubjectivityRoot(context.Background()); (err != nil) != tt.wantErr {
-				require.ErrorContains(t, tt.errString, err)
+			s.store.SetFinalizedCheckpt(&ethpb.Checkpoint{Epoch: tt.finalizedEpoch})
+			err = s.wsVerifier.VerifyWeakSubjectivity(context.Background(), s.store.FinalizedCheckpt().Epoch)
+			if tt.wantErr == nil {
+				require.NoError(t, err)
+			} else {
+				require.Equal(t, true, errors.Is(err, tt.wantErr))
 			}
 		})
 	}
--- a/beacon-chain/cache/BUILD.bazel
+++ b/beacon-chain/cache/BUILD.bazel
@@ -1,53 +1,45 @@
 load("@prysm//tools/go:def.bzl", "go_library", "go_test")

-# gazelle:exclude committee_disabled.go
-# gazelle:exclude proposer_indices_disabled.go
 go_library(
    name = "go_default_library",
    srcs = [
+        "active_balance.go",
+        "active_balance_disabled.go",  # keep
        "attestation_data.go",
        "checkpoint_state.go",
+        "committee.go",
+        "committee_disabled.go",  # keep
        "committees.go",
        "common.go",
        "doc.go",
        "error.go",
+        "proposer_indices.go",
+        "proposer_indices_disabled.go",  # keep
        "proposer_indices_type.go",
        "skip_slot_cache.go",
        "subnet_ids.go",
+        "sync_committee.go",
+        "sync_committee_disabled.go",  # keep
        "sync_committee_head_state.go",
        "sync_subnet_ids.go",
-    ] + select({
-        "//testing/fuzz:fuzzing_enabled": [
-            "active_balance_disabled.go",
-            "committee_disabled.go",
-            "proposer_indices_disabled.go",
-            "sync_committee_disabled.go",
-        ],
-        "//conditions:default": [
-            "active_balance.go",
-            "committee.go",
-            "proposer_indices.go",
-            "sync_committee.go",
-        ],
-    }),
+    ],
    importpath = "github.com/prysmaticlabs/prysm/beacon-chain/cache",
    visibility = [
        "//beacon-chain:__subpackages__",
-        "//testing/fuzz:__pkg__",
        "//tools:__subpackages__",
    ],
    deps = [
        "//beacon-chain/state:go_default_library",
-        "//beacon-chain/state/v2:go_default_library",
        "//cache/lru:go_default_library",
        "//config/features:go_default_library",
+        "//config/params:go_default_library",
        "//container/slice:go_default_library",
        "//crypto/hash:go_default_library",
        "//crypto/rand:go_default_library",
+        "//encoding/bytesutil:go_default_library",
        "//math:go_default_library",
        "//proto/prysm/v1alpha1:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "//shared/params:go_default_library",
+        "//runtime/version:go_default_library",
        "@com_github_hashicorp_golang_lru//:go_default_library",
        "@com_github_patrickmn_go_cache//:go_default_library",
        "@com_github_pkg_errors//:go_default_library",
@@ -81,13 +73,15 @@ go_test(
        "//beacon-chain/state:go_default_library",
        "//beacon-chain/state/v1:go_default_library",
        "//beacon-chain/state/v2:go_default_library",
+        "//beacon-chain/state/v3:go_default_library",
        "//config/features:go_default_library",
+        "//config/fieldparams:go_default_library",
+        "//config/params:go_default_library",
+        "//encoding/bytesutil:go_default_library",
        "//proto/prysm/v1alpha1:go_default_library",
-        "//shared/bytesutil:go_default_library",
-        "//shared/params:go_default_library",
-        "//shared/testutil:go_default_library",
-        "//shared/testutil/assert:go_default_library",
-        "//shared/testutil/require:go_default_library",
+        "//testing/assert:go_default_library",
+        "//testing/require:go_default_library",
+        "//testing/util:go_default_library",
        "@com_github_google_gofuzz//:go_default_library",
        "@com_github_prysmaticlabs_eth2_types//:go_default_library",
        "@org_golang_google_protobuf//proto:go_default_library",
--- a/beacon-chain/cache/active_balance.go
+++ b/beacon-chain/cache/active_balance.go
@@ -1,4 +1,4 @@
-// +build !libfuzzer
+// +build !fuzz

 package cache

@@ -14,7 +14,7 @@ import (
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
 	lruwrpr "github.com/prysmaticlabs/prysm/cache/lru"
 	"github.com/prysmaticlabs/prysm/config/features"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/config/params"
 )

 var (
--- a/beacon-chain/cache/active_balance_disabled.go
+++ b/beacon-chain/cache/active_balance_disabled.go
@@ -1,4 +1,4 @@
-// +build libfuzzer
+// +build fuzz

 package cache

--- a/beacon-chain/cache/active_balance_test.go
+++ b/beacon-chain/cache/active_balance_test.go
@@ -8,9 +8,9 @@ import (
 	types "github.com/prysmaticlabs/eth2-types"
 	state "github.com/prysmaticlabs/prysm/beacon-chain/state/v1"
 	"github.com/prysmaticlabs/prysm/config/features"
+	"github.com/prysmaticlabs/prysm/config/params"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 func TestBalanceCache_AddGetBalance(t *testing.T) {
--- a/beacon-chain/cache/attestation_data_test.go
+++ b/beacon-chain/cache/attestation_data_test.go
@@ -6,7 +6,7 @@ import (

 	"github.com/prysmaticlabs/prysm/beacon-chain/cache"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
+	"github.com/prysmaticlabs/prysm/testing/assert"
 	"google.golang.org/protobuf/proto"
 )

--- a/beacon-chain/cache/checkpoint_state_test.go
+++ b/beacon-chain/cache/checkpoint_state_test.go
@@ -6,11 +6,11 @@ import (
 	types "github.com/prysmaticlabs/eth2-types"
 	"github.com/prysmaticlabs/prysm/beacon-chain/state"
 	v1 "github.com/prysmaticlabs/prysm/beacon-chain/state/v1"
+	"github.com/prysmaticlabs/prysm/config/params"
+	"github.com/prysmaticlabs/prysm/encoding/bytesutil"
 	ethpb "github.com/prysmaticlabs/prysm/proto/prysm/v1alpha1"
-	"github.com/prysmaticlabs/prysm/shared/bytesutil"
-	"github.com/prysmaticlabs/prysm/shared/params"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 	"google.golang.org/protobuf/proto"
 )

--- a/beacon-chain/cache/committee.go
+++ b/beacon-chain/cache/committee.go
@@ -1,19 +1,22 @@
-// +build !libfuzzer
+// +build !fuzz

 package cache

 import (
+	"context"
 	"errors"
+	"math"
 	"sync"
+	"time"

 	lru "github.com/hashicorp/golang-lru"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	types "github.com/prysmaticlabs/eth2-types"
 	lruwrpr "github.com/prysmaticlabs/prysm/cache/lru"
+	"github.com/prysmaticlabs/prysm/config/params"
 	"github.com/prysmaticlabs/prysm/container/slice"
-	"github.com/prysmaticlabs/prysm/math"
-	"github.com/prysmaticlabs/prysm/shared/params"
+	mathutil "github.com/prysmaticlabs/prysm/math"
 )

 var (
@@ -37,6 +40,7 @@ var (
 type CommitteeCache struct {
 	CommitteeCache *lru.Cache
 	lock           sync.RWMutex
+	inProgress     map[string]bool
 }

 // committeeKeyFn takes the seed as the key to retrieve shuffled indices of a committee in a given epoch.
@@ -52,14 +56,16 @@ func committeeKeyFn(obj interface{}) (string, error) {
 func NewCommitteesCache() *CommitteeCache {
 	return &CommitteeCache{
 		CommitteeCache: lruwrpr.New(int(maxCommitteesCacheSize)),
+		inProgress:     make(map[string]bool),
 	}
 }

 // Committee fetches the shuffled indices by slot and committee index. Every list of indices
 // represent one committee. Returns true if the list exists with slot and committee index. Otherwise returns false, nil.
-func (c *CommitteeCache) Committee(slot types.Slot, seed [32]byte, index types.CommitteeIndex) ([]types.ValidatorIndex, error) {
-	c.lock.RLock()
-	defer c.lock.RUnlock()
+func (c *CommitteeCache) Committee(ctx context.Context, slot types.Slot, seed [32]byte, index types.CommitteeIndex) ([]types.ValidatorIndex, error) {
+	if err := c.checkInProgress(ctx, seed); err != nil {
+		return nil, err
+	}

 	obj, exists := c.CommitteeCache.Get(key(seed))
 	if exists {
@@ -79,7 +85,7 @@ func (c *CommitteeCache) Committee(slot types.Slot, seed [32]byte, index types.C
 		committeeCountPerSlot = item.CommitteeCount / uint64(params.BeaconConfig().SlotsPerEpoch)
 	}

-	indexOffSet, err := math.Add64(uint64(index), uint64(slot.ModSlot(params.BeaconConfig().SlotsPerEpoch).Mul(committeeCountPerSlot)))
+	indexOffSet, err := mathutil.Add64(uint64(index), uint64(slot.ModSlot(params.BeaconConfig().SlotsPerEpoch).Mul(committeeCountPerSlot)))
 	if err != nil {
 		return nil, err
 	}
@@ -106,9 +112,10 @@ func (c *CommitteeCache) AddCommitteeShuffledList(committees *Committees) error
 }

 // ActiveIndices returns the active indices of a given seed stored in cache.
-func (c *CommitteeCache) ActiveIndices(seed [32]byte) ([]types.ValidatorIndex, error) {
-	c.lock.RLock()
-	defer c.lock.RUnlock()
+func (c *CommitteeCache) ActiveIndices(ctx context.Context, seed [32]byte) ([]types.ValidatorIndex, error) {
+	if err := c.checkInProgress(ctx, seed); err != nil {
+		return nil, err
+	}
 	obj, exists := c.CommitteeCache.Get(key(seed))

 	if exists {
@@ -127,9 +134,11 @@ func (c *CommitteeCache) ActiveIndices(seed [32]byte) ([]types.ValidatorIndex, e
 }

 // ActiveIndicesCount returns the active indices count of a given seed stored in cache.
-func (c *CommitteeCache) ActiveIndicesCount(seed [32]byte) (int, error) {
-	c.lock.RLock()
-	defer c.lock.RUnlock()
+func (c *CommitteeCache) ActiveIndicesCount(ctx context.Context, seed [32]byte) (int, error) {
+	if err := c.checkInProgress(ctx, seed); err != nil {
+		return 0, err
+	}
+
 	obj, exists := c.CommitteeCache.Get(key(seed))
 	if exists {
 		CommitteeCacheHit.Inc()
@@ -152,6 +161,29 @@ func (c *CommitteeCache) HasEntry(seed string) bool {
 	return ok
 }

+// MarkInProgress a request so that any other similar requests will block on
+// Get until MarkNotInProgress is called.
+func (c *CommitteeCache) MarkInProgress(seed [32]byte) error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	s := key(seed)
+	if c.inProgress[s] {
+		return ErrAlreadyInProgress
+	}
+	c.inProgress[s] = true
+	return nil
+}
+
+// MarkNotInProgress will release the lock on a given request. This should be
+// called after put.
+func (c *CommitteeCache) MarkNotInProgress(seed [32]byte) error {
+	c.lock.Lock()
+	defer c.lock.Unlock()
+	s := key(seed)
+	delete(c.inProgress, s)
+	return nil
+}
+
 func startEndIndices(c *Committees, index uint64) (uint64, uint64) {
 	validatorCount := uint64(len(c.ShuffledIndices))
 	start := slice.SplitOffset(validatorCount, c.CommitteeCount, index)
@@ -166,3 +198,28 @@ func startEndIndices(c *Committees, index uint64) (uint64, uint64) {
 func key(seed [32]byte) string {
 	return string(seed[:])
 }
+
+func (c *CommitteeCache) checkInProgress(ctx context.Context, seed [32]byte) error {
+	delay := minDelay
+	// Another identical request may be in progress already. Let's wait until
+	// any in progress request resolves or our timeout is exceeded.
+	for {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+
+		c.lock.RLock()
+		if !c.inProgress[key(seed)] {
+			c.lock.RUnlock()
+			break
+		}
+		c.lock.RUnlock()
+
+		// This increasing backoff is to decrease the CPU cycles while waiting
+		// for the in progress boolean to flip to false.
+		time.Sleep(time.Duration(delay) * time.Nanosecond)
+		delay *= delayFactor
+		delay = math.Min(delay, maxDelay)
+	}
+	return nil
+}
--- a/beacon-chain/cache/committee_disabled.go
+++ b/beacon-chain/cache/committee_disabled.go
@@ -1,9 +1,13 @@
-// +build libfuzzer
+// +build fuzz

 // This file is used in fuzzer builds to bypass global committee caches.
 package cache

-import types "github.com/prysmaticlabs/eth2-types"
+import (
+	"context"
+
+	types "github.com/prysmaticlabs/eth2-types"
+)

 // FakeCommitteeCache is a struct with 1 queue for looking up shuffled indices list by seed.
 type FakeCommitteeCache struct {
@@ -16,7 +20,7 @@ func NewCommitteesCache() *FakeCommitteeCache {

 // Committee fetches the shuffled indices by slot and committee index. Every list of indices
 // represent one committee. Returns true if the list exists with slot and committee index. Otherwise returns false, nil.
-func (c *FakeCommitteeCache) Committee(slot types.Slot, seed [32]byte, index types.CommitteeIndex) ([]types.ValidatorIndex, error) {
+func (c *FakeCommitteeCache) Committee(ctx context.Context, slot types.Slot, seed [32]byte, index types.CommitteeIndex) ([]types.ValidatorIndex, error) {
 	return nil, nil
 }

@@ -32,12 +36,12 @@ func (c *FakeCommitteeCache) AddProposerIndicesList(seed [32]byte, indices []typ
 }

 // ActiveIndices returns the active indices of a given seed stored in cache.
-func (c *FakeCommitteeCache) ActiveIndices(seed [32]byte) ([]types.ValidatorIndex, error) {
+func (c *FakeCommitteeCache) ActiveIndices(ctx context.Context, seed [32]byte) ([]types.ValidatorIndex, error) {
 	return nil, nil
 }

 // ActiveIndicesCount returns the active indices count of a given seed stored in cache.
-func (c *FakeCommitteeCache) ActiveIndicesCount(seed [32]byte) (int, error) {
+func (c *FakeCommitteeCache) ActiveIndicesCount(ctx context.Context, seed [32]byte) (int, error) {
 	return 0, nil
 }

@@ -55,3 +59,13 @@ func (c *FakeCommitteeCache) ProposerIndices(seed [32]byte) ([]types.ValidatorIn
 func (c *FakeCommitteeCache) HasEntry(string) bool {
 	return false
 }
+
+// MarkInProgress is a stub.
+func (c *FakeCommitteeCache) MarkInProgress(seed [32]byte) error {
+	return nil
+}
+
+// MarkNotInProgress is a stub.
+func (c *FakeCommitteeCache) MarkNotInProgress(seed [32]byte) error {
+	return nil
+}
--- a/beacon-chain/cache/committee_fuzz_test.go
+++ b/beacon-chain/cache/committee_fuzz_test.go
@@ -1,11 +1,12 @@
 package cache

 import (
+	"context"
 	"testing"

 	fuzz "github.com/google/gofuzz"
-	"github.com/prysmaticlabs/prysm/shared/testutil/assert"
-	"github.com/prysmaticlabs/prysm/shared/testutil/require"
+	"github.com/prysmaticlabs/prysm/testing/assert"
+	"github.com/prysmaticlabs/prysm/testing/require"
 )

 func TestCommitteeKeyFuzz_OK(t *testing.T) {
@@ -28,7 +29,7 @@ func TestCommitteeCache_FuzzCommitteesByEpoch(t *testing.T) {
 	for i := 0; i < 100000; i++ {
 		fuzzer.Fuzz(c)
 		require.NoError(t, cache.AddCommitteeShuffledList(c))
-		_, err := cache.Committee(0, c.Seed, 0)
+		_, err := cache.Committee(context.Background(), 0, c.Seed, 0)
 		require.NoError(t, err)
 	}

@@ -44,7 +45,7 @@ func TestCommitteeCache_FuzzActiveIndices(t *testing.T) {
 		fuzzer.Fuzz(c)
 		require.NoError(t, cache.AddCommitteeShuffledList(c))

-		indices, err := cache.ActiveIndices(c.Seed)
+		indices, err := cache.ActiveIndices(context.Background(), c.Seed)
 		require.NoError(t, err)
 		assert.DeepEqual(t, c.SortedIndices, indices)
 	}
--- a/Show More
+++ b/Show More
@@ -1 +1 @@
 .7.0
 .2.2