diff --git a/Makefile b/Makefile
index 1c7f84ec6..65c8bc33d 100644
--- a/Makefile
+++ b/Makefile
@@ -13,7 +13,11 @@ YAML_TEST_TARGETS = $(patsubst $(GENERATOR_DIR)/%, $(YAML_TEST_DIR)/%, $(GENERAT
 GENERATOR_VENVS = $(patsubst $(GENERATOR_DIR)/%, $(GENERATOR_DIR)/%venv, $(GENERATORS))
 
 PY_SPEC_PHASE_0_TARGETS = $(PY_SPEC_DIR)/eth2spec/phase0/spec.py
+PY_SPEC_PHASE_0_DEPS = $(SPEC_DIR)/core/0_*.md
+
 PY_SPEC_PHASE_1_TARGETS = $(PY_SPEC_DIR)/eth2spec/phase1/custody_game.py $(PY_SPEC_DIR)/eth2spec/phase1/shard_data_chains.py
+PY_SPEC_PHASE_1_DEPS = $(SPEC_DIR)/core/1_*.md
+
 PY_SPEC_ALL_TARGETS = $(PY_SPEC_PHASE_0_TARGETS)
 
 
@@ -50,13 +54,13 @@ phase0: $(PY_SPEC_PHASE_0_TARGETS)
 # "make phase1" to create pyspec for phase1
 phase1: $(PY_SPEC_PHASE_1_TARGETS)
 
-$(PY_SPEC_DIR)/eth2spec/phase0/spec.py:
+$(PY_SPEC_DIR)/eth2spec/phase0/spec.py: $(PY_SPEC_PHASE_0_DEPS)
 	python3 $(SCRIPT_DIR)/phase0/build_spec.py  $(SPEC_DIR)/core/0_beacon-chain.md $@
 
-$(PY_SPEC_DIR)/eth2spec/phase1/custody_game.py:
+$(PY_SPEC_DIR)/eth2spec/phase1/custody_game.py: $(PY_SPEC_PHASE_1_DEPS)
 	python3 $(SCRIPT_DIR)/phase0/build_spec.py -p1  $(SPEC_DIR)/core/1_custody-game.md $@
 
-$(PY_SPEC_DIR)/eth2spec/phase1/shard_data_chains.py:
+$(PY_SPEC_DIR)/eth2spec/phase1/shard_data_chains.py: $(PY_SPEC_PHASE_0_DEPS)
 	python3 $(SCRIPT_DIR)/phase0/build_spec.py -p1 $(SPEC_DIR)/core/1_shard-data-chains.md $@
 
 
diff --git a/scripts/phase0/build_spec.py b/scripts/phase0/build_spec.py
index 80b378fbb..e3009004f 100644
--- a/scripts/phase0/build_spec.py
+++ b/scripts/phase0/build_spec.py
@@ -89,11 +89,29 @@ def build_phase1_spec(sourcefile, outfile):
     code_lines = []
     code_lines.append("""
 from eth2spec.phase0.spec import *
+from eth2spec.phase0.spec import apply_constants_preset as apply_constants_preset_phase0
 
 """)
 
     code_lines += function_puller.get_spec(sourcefile)
 
+    code_lines.append("""
+# Access to overwrite spec constants based on configuration
+def apply_constants_preset(preset: Dict[str, Any]):
+
+    apply_constants_preset_phase0(preset)
+
+    global_vars = globals()
+    for k, v in preset.items():
+        global_vars[k] = v
+
+    # Deal with derived constants
+    global_vars['GENESIS_EPOCH'] = slot_to_epoch(GENESIS_SLOT)
+
+    # Initialize SSZ types again, to account for changed lengths
+    init_SSZ_types()
+""")
+
     with open(outfile, 'w') as out:
         out.write("\n".join(code_lines))
 
diff --git a/scripts/phase0/function_puller.py b/scripts/phase0/function_puller.py
index 830e52a32..26ac2f17f 100644
--- a/scripts/phase0/function_puller.py
+++ b/scripts/phase0/function_puller.py
@@ -39,10 +39,11 @@ def get_spec(file_name: str, phase:int = 0) -> List[str]:
         else:
             if pulling_from == linenum and line == '{':
                 if is_update_section:
-                    code_lines.append('%s = SSZTypeExtension(%s, {' % (current_name, current_name))
+                    code_lines.append('%s = SSZTypeExtension("%s", {' % (current_name, current_name))
+                    current_typedef = ['global_vars["%s"] = SSZTypeExtension("%s", {' % (current_name, current_name)]
                 else:
-                    code_lines.append('%s = SSZType({' % current_name)
-                current_typedef = ['global_vars["%s"] = SSZType({' % current_name]
+                    code_lines.append('%s = SSZType("%s", {' % (current_name, current_name))
+                    current_typedef = ['global_vars["%s"] = SSZType("%s", {' % (current_name, current_name)]
             elif pulling_from is not None:
                 # Add some whitespace between functions
                 if line[:3] == 'def':
diff --git a/specs/core/1_custody-game.md b/specs/core/1_custody-game.md
index 5de52a4ea..501bfce46 100644
--- a/specs/core/1_custody-game.md
+++ b/specs/core/1_custody-game.md
@@ -661,12 +661,12 @@ def process_bit_challenge_response(state: BeaconState,
 
 ### Handling of custody-related deadlines
 
-Run `process_reveal_deadlines(state)` immediately after `process_ejections(state)`:
+Run `process_reveal_deadlines(state)` immediately after `process_registry_updates(state)`:
 
 ```python
 def process_reveal_deadlines(state: BeaconState) -> None:
     for index, validator in enumerate(state.validator_registry):
-        if (validator.latest_custody_reveal_period +
+        if (validator.next_custody_reveal_period +
             (CUSTODY_RESPONSE_DEADLINE // EPOCHS_PER_CUSTODY_PERIOD) <
             get_validators_custody_reveal_period(state, index)):
                 slash_validator(state, index)
@@ -693,6 +693,7 @@ Append this to `process_final_updates(state)`:
 
 ```python
 def after_process_final_updates(state: BeaconState) -> None:
+    current_epoch = get_current_epoch(state)
     # Clean up exposed RANDAO key reveals
     state.exposed_derived_secrets[current_epoch % EARLY_DERIVED_SECRET_PENALTY_MAX_FUTURE_EPOCHS] = []
 ```
diff --git a/test_libs/pyspec/eth2spec/phase1/__init__.py b/test_libs/pyspec/eth2spec/phase1/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/test_libs/pyspec/eth2spec/phase1/state_transition.py b/test_libs/pyspec/eth2spec/phase1/state_transition.py
new file mode 100644
index 000000000..7e6411287
--- /dev/null
+++ b/test_libs/pyspec/eth2spec/phase1/state_transition.py
@@ -0,0 +1,77 @@
+from . import spec
+
+from typing import (
+    Any,
+    Callable,
+    List
+)
+
+from .spec import (
+    BeaconState,
+    BeaconBlock,
+    Slot,
+)
+
+from eth2spec.phase0.state_transition import (
+    expected_deposit_count,
+    process_operation_type,
+    process_operations as process_operations_phase0,
+    process_block as process_block_phase0,
+    process_epoch_transition as process_epoch_transition_phase0,
+    state_transition_to as state_transition_to_phase0,
+    state_transition as state_transition_phase0
+)
+
+def process_operations(state: BeaconState, block: BeaconBlock) -> None:
+    process_operations_phase0(state, block)
+    
+    process_operation_type(
+        state,
+        block.body.custody_key_reveals,
+        spec.MAX_CUSTODY_KEY_REVEALS,
+        spec.process_custody_key_reveal,
+    )
+
+    process_operation_type(
+        state,
+        block.body.early_derived_secret_reveals,
+        spec.MAX_EARLY_DERIVED_SECRET_REVEALS,
+        spec.process_early_derived_secret_reveal,
+    )
+
+def process_block(state: BeaconState,
+                  block: BeaconBlock,
+                  verify_state_root: bool=False) -> None:
+    spec.process_block_header(state, block)
+    spec.process_randao(state, block)
+    spec.process_eth1_data(state, block)
+
+    process_operations(state, block)
+    if verify_state_root:
+        spec.verify_block_state_root(state, block)
+
+def process_epoch_transition(state: BeaconState) -> None:
+    spec.process_justification_and_finalization(state)
+    spec.process_crosslinks(state)
+    # TODO: Eligible
+    spec.process_rewards_and_penalties(state)
+    spec.process_registry_updates(state)
+    spec.process_reveal_deadlines(state)
+    spec.process_challenge_deadlines(state)
+    spec.process_slashings(state)
+    spec.process_final_updates(state)
+    spec.after_process_final_updates(state)
+
+def state_transition_to(state: BeaconState, up_to: Slot) -> BeaconState:
+    while state.slot < up_to:
+        spec.cache_state(state)
+        if (state.slot + 1) % spec.SLOTS_PER_EPOCH == 0:
+            process_epoch_transition(state)
+        spec.advance_slot(state)
+
+
+def state_transition(state: BeaconState,
+                     block: BeaconBlock,
+                     verify_state_root: bool=False) -> BeaconState:
+    state_transition_to(state, block.slot)
+    process_block(state, block, verify_state_root)
\ No newline at end of file
diff --git a/test_libs/pyspec/eth2spec/utils/minimal_ssz.py b/test_libs/pyspec/eth2spec/utils/minimal_ssz.py
index cfd2e56ac..8a210f41b 100644
--- a/test_libs/pyspec/eth2spec/utils/minimal_ssz.py
+++ b/test_libs/pyspec/eth2spec/utils/minimal_ssz.py
@@ -6,9 +6,14 @@ BYTES_PER_CHUNK = 32
 BYTES_PER_LENGTH_OFFSET = 4
 ZERO_CHUNK = b'\x00' * BYTES_PER_CHUNK
 
+cached_typedefs = {}
 
-def SSZType(fields):
+def SSZType(name, fields):
     class SSZObject():
+        if name != None:
+            __name__ = name
+            __qualname__ = name
+        
         def __init__(self, **kwargs):
             for f, t in fields.items():
                 if f not in kwargs:
@@ -25,8 +30,11 @@ def SSZType(fields):
         def __str__(self):
             output = []
             for field in self.fields:
-                output.append(f'{field}: {getattr(self, field)}')
+                output.append(f'{field}: {repr(getattr(self, field))},')
             return "\n".join(output)
+        
+        def __repr__(self):
+            return name + "(**{\n    " + str(self).replace("\n", "\n    ") + "\n})"
 
         def serialize(self):
             return serialize_value(self, self.__class__)
@@ -35,12 +43,16 @@ def SSZType(fields):
             return hash_tree_root(self, self.__class__)
 
     SSZObject.fields = fields
+    
+    if name != None:
+        cached_typedefs[name] = SSZObject
+
     return SSZObject
 
 def SSZTypeExtension(original_type, new_fields):
-    fields = original_type.fields.copy()
-    fields.update(original_type.fields)
-    return SSZType(fields)
+    typedef = cached_typedefs[original_type]
+    typedef.fields.update(new_fields)
+    return typedef
 
 class Vector():
     def __init__(self, items):
@@ -319,7 +331,7 @@ def truncate(container):
         key: container.fields[key]
         for key in field_keys[:-1]
     }
-    truncated_class = SSZType(truncated_fields)
+    truncated_class = SSZType(None, truncated_fields)
     kwargs = {
         field: getattr(container, field)
         for field in field_keys[:-1]
diff --git a/test_libs/pyspec/tests/block_processing/test_process_attestation.py b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
index bcf71376c..18706c9e5 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_attestation.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attestation.py
@@ -1,12 +1,12 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.state_transition import (
+from eth2spec.phase1.state_transition import (
     state_transition,
 )
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     get_current_epoch,
     process_attestation,
     slot_to_epoch,
diff --git a/test_libs/pyspec/tests/block_processing/test_process_attester_slashing.py b/test_libs/pyspec/tests/block_processing/test_process_attester_slashing.py
index 2ea16f13d..880ca829a 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_attester_slashing.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_attester_slashing.py
@@ -1,8 +1,8 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
-from eth2spec.phase0.spec import (
+import eth2spec.phase1.spec as spec
+from eth2spec.phase1.spec import (
     get_beacon_proposer_index,
     process_attester_slashing,
 )
diff --git a/test_libs/pyspec/tests/block_processing/test_process_block_header.py b/test_libs/pyspec/tests/block_processing/test_process_block_header.py
index b35b0a9c1..bcaf3c6d8 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_block_header.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_block_header.py
@@ -2,7 +2,7 @@ from copy import deepcopy
 import pytest
 
 
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     get_beacon_proposer_index,
     cache_state,
     advance_slot,
diff --git a/test_libs/pyspec/tests/block_processing/test_process_deposit.py b/test_libs/pyspec/tests/block_processing/test_process_deposit.py
index bbfb390ef..768f61678 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_deposit.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_deposit.py
@@ -1,9 +1,9 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     ZERO_HASH,
     process_deposit,
 )
diff --git a/test_libs/pyspec/tests/block_processing/test_process_proposer_slashing.py b/test_libs/pyspec/tests/block_processing/test_process_proposer_slashing.py
index 475221036..513e607b1 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_proposer_slashing.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_proposer_slashing.py
@@ -1,8 +1,8 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
-from eth2spec.phase0.spec import (
+import eth2spec.phase1.spec as spec
+from eth2spec.phase1.spec import (
     get_current_epoch,
     process_proposer_slashing,
 )
diff --git a/test_libs/pyspec/tests/block_processing/test_process_transfer.py b/test_libs/pyspec/tests/block_processing/test_process_transfer.py
index 0eeaa7792..02f448fd0 100644
--- a/test_libs/pyspec/tests/block_processing/test_process_transfer.py
+++ b/test_libs/pyspec/tests/block_processing/test_process_transfer.py
@@ -1,9 +1,9 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     get_active_validator_indices,
     get_beacon_proposer_index,
     get_current_epoch,
diff --git a/test_libs/pyspec/tests/block_processing/test_voluntary_exit.py b/test_libs/pyspec/tests/block_processing/test_voluntary_exit.py
index c58c5238a..c789b55d8 100644
--- a/test_libs/pyspec/tests/block_processing/test_voluntary_exit.py
+++ b/test_libs/pyspec/tests/block_processing/test_voluntary_exit.py
@@ -1,9 +1,9 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     get_active_validator_indices,
     get_churn_limit,
     get_current_epoch,
diff --git a/test_libs/pyspec/tests/conftest.py b/test_libs/pyspec/tests/conftest.py
index 9840dc7b2..98b64c73b 100644
--- a/test_libs/pyspec/tests/conftest.py
+++ b/test_libs/pyspec/tests/conftest.py
@@ -1,6 +1,6 @@
 import pytest
 
-from eth2spec.phase0 import spec
+from eth2spec.phase1 import spec
 from preset_loader import loader
 
 from .helpers import (
@@ -20,7 +20,6 @@ def config(request):
     presets = loader.load_presets('../../configs/', config_name)
     spec.apply_constants_preset(presets)
 
-
 @pytest.fixture
 def num_validators(config):
     return spec.SLOTS_PER_EPOCH * 8
diff --git a/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py b/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
index d6765e3a7..9a6254715 100644
--- a/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
+++ b/test_libs/pyspec/tests/epoch_processing/test_process_crosslinks.py
@@ -1,12 +1,12 @@
 from copy import deepcopy
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.state_transition import (
+from eth2spec.phase1.state_transition import (
     state_transition,
 )
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     cache_state,
     get_crosslink_deltas,
     process_crosslinks,
diff --git a/test_libs/pyspec/tests/epoch_processing/test_process_registry_updates.py b/test_libs/pyspec/tests/epoch_processing/test_process_registry_updates.py
index 11f5de2ad..15f7ae6ec 100644
--- a/test_libs/pyspec/tests/epoch_processing/test_process_registry_updates.py
+++ b/test_libs/pyspec/tests/epoch_processing/test_process_registry_updates.py
@@ -2,9 +2,9 @@ from copy import deepcopy
 
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     get_current_epoch,
     is_active_validator,
 )
diff --git a/test_libs/pyspec/tests/helpers.py b/test_libs/pyspec/tests/helpers.py
index 3b9b6904d..3156a7f28 100644
--- a/test_libs/pyspec/tests/helpers.py
+++ b/test_libs/pyspec/tests/helpers.py
@@ -2,12 +2,12 @@ from copy import deepcopy
 
 from py_ecc import bls
 
-from eth2spec.phase0.state_transition import (
+from eth2spec.phase1.state_transition import (
     state_transition,
 )
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 from eth2spec.utils.minimal_ssz import signing_root
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     # constants
     ZERO_HASH,
     # SSZ
@@ -420,3 +420,6 @@ def get_state_root(state, slot) -> bytes:
     """
     assert slot < state.slot <= slot + spec.SLOTS_PER_HISTORICAL_ROOT
     return state.latest_state_roots[slot % spec.SLOTS_PER_HISTORICAL_ROOT]
+
+# Stub to be overwritten by config
+import_spec = None
\ No newline at end of file
diff --git a/test_libs/pyspec/tests/test_finality.py b/test_libs/pyspec/tests/test_finality.py
index ca048c2b2..46f08cfbb 100644
--- a/test_libs/pyspec/tests/test_finality.py
+++ b/test_libs/pyspec/tests/test_finality.py
@@ -2,9 +2,9 @@ from copy import deepcopy
 
 import pytest
 
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
-from eth2spec.phase0.state_transition import (
+from eth2spec.phase1.state_transition import (
     state_transition,
 )
 from .helpers import (
diff --git a/test_libs/pyspec/tests/test_sanity.py b/test_libs/pyspec/tests/test_sanity.py
index 1b4d20f4c..ea488fd1f 100644
--- a/test_libs/pyspec/tests/test_sanity.py
+++ b/test_libs/pyspec/tests/test_sanity.py
@@ -3,10 +3,10 @@ from copy import deepcopy
 import pytest
 
 from py_ecc import bls
-import eth2spec.phase0.spec as spec
+import eth2spec.phase1.spec as spec
 
 from eth2spec.utils.minimal_ssz import signing_root
-from eth2spec.phase0.spec import (
+from eth2spec.phase1.spec import (
     # constants
     ZERO_HASH,
     SLOTS_PER_HISTORICAL_ROOT,
@@ -25,7 +25,7 @@ from eth2spec.phase0.spec import (
     verify_merkle_branch,
     hash,
 )
-from eth2spec.phase0.state_transition import (
+from eth2spec.phase1.state_transition import (
     state_transition,
 )
 from eth2spec.utils.merkle_minimal import (
@@ -326,7 +326,7 @@ def test_voluntary_exit(state):
 
 def test_transfer(state):
     # overwrite default 0 to test
-    spec.MAX_TRANSFERS = 1
+    spec.apply_constants_preset({"MAX_TRANSFERS": 1})
 
     pre_state = deepcopy(state)
     current_epoch = get_current_epoch(pre_state)