diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6bc2d423b6..1cb094fc2f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -23,6 +23,7 @@ Docs: https://docs.openclaw.ai
 - Scripts/UI/Windows: fix `pnpm ui:*` spawn `EINVAL` failures by restoring shell-backed launch for `.cmd`/`.bat` runners, narrowing shell usage to launcher types that require it, and rejecting unsafe forwarded shell metacharacters in UI script args. (#18594)
 - Hooks/Session-memory: recover `/new` conversation summaries when session pointers are reset-path or missing `sessionFile`, and consistently prefer the newest `.jsonl.reset.*` transcript candidate for fallback extraction. (#18088)
 - Slack: restrict forwarded-attachment ingestion to explicit shared-message attachments and skip non-Slack forwarded `image_url` fetches, preventing non-forward attachment unfurls from polluting inbound agent context while preserving forwarded message handling.
+- Slack: validate `channels.slack.streamMode` for the new Slack streaming mode options (`replace|status_final|append`) in provider schema and default to `replace`.
 - Agents/Sessions: align session lock watchdog hold windows with run and compaction timeout budgets (plus grace), preventing valid long-running turns from being force-unlocked mid-run while still recovering hung lock owners. (#18060)
 - Cron/Heartbeat: canonicalize session-scoped reminder `sessionKey` routing and preserve explicit flat `sessionKey` cron tool inputs, preventing enqueue/wake namespace drift for session-targeted reminders. (#18637) Thanks @vignesh07.
 - OpenClawKit/iOS ChatUI: accept canonical session-key completion events for local pending runs and preserve message IDs across history refreshes, preventing stuck "thinking" state and message flicker after gateway replies. (#18165) Thanks @mbelinky.
diff --git a/src/config/config.schema-regressions.test.ts b/src/config/config.schema-regressions.test.ts
index ffe204bc68..c9dfbfa41c 100644
--- a/src/config/config.schema-regressions.test.ts
+++ b/src/config/config.schema-regressions.test.ts
@@ -36,4 +36,16 @@ describe("config schema regressions", () => {
 
     expect(res.ok).toBe(true);
   });
+
+  it("accepts channels.slack.streamMode", () => {
+    const res = validateConfigObject({
+      channels: {
+        slack: {
+          streamMode: "append",
+        },
+      },
+    });
+
+    expect(res.ok).toBe(true);
+  });
 });
diff --git a/src/config/zod-schema.providers-core.ts b/src/config/zod-schema.providers-core.ts
index 319c167b3c..ef1828d8fb 100644
--- a/src/config/zod-schema.providers-core.ts
+++ b/src/config/zod-schema.providers-core.ts
@@ -460,7 +460,6 @@ export const GoogleChatAccountSchema = z
     chunkMode: z.enum(["length", "newline"]).optional(),
     blockStreaming: z.boolean().optional(),
     blockStreamingCoalesce: BlockStreamingCoalesceSchema.optional(),
-    streamMode: z.enum(["replace", "status_final", "append"]).optional().default("replace"),
     mediaMaxMb: z.number().positive().optional(),
     replyToMode: ReplyToModeSchema.optional(),
     actions: z
@@ -578,6 +577,7 @@ export const SlackAccountSchema = z
     // inheritance in multi-account setups (shallow merge works; nested dm object doesn't).
     dmPolicy: DmPolicySchema.optional(),
     allowFrom: z.array(z.union([z.string(), z.number()])).optional(),
+    streamMode: z.enum(["replace", "status_final", "append"]).optional().default("replace"),
     dm: SlackDmSchema.optional(),
     channels: z.record(z.string(), SlackChannelSchema.optional()).optional(),
     heartbeat: ChannelHeartbeatVisibilitySchema,