compaction: add configurable model override

Allow users to specify a different model for compaction summarization
via `agents.defaults.compaction.model`. When set, compaction uses
this model instead of the agent's primary model.

This is useful for hybrid local+cloud setups where the primary model
is a small local model (e.g. Ollama/Qwen) but compaction benefits
from a more capable summarizer (e.g. cloud Claude), or a dedicated
local model fine-tuned for summarization.

Config example:
  "compaction": { "model": "openrouter/anthropic/claude-sonnet-4-5" }

Falls back to the primary model when unset (no behavior change for
existing configs).

Closes #7926

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/concepts/compaction.md

@@ -24,6 +24,36 @@ Compaction **persists** in the session’s JSONL history.
 Use the `agents.defaults.compaction` setting in your `openclaw.json` to configure compaction behavior (mode, target tokens, etc.).
 Compaction summarization preserves opaque identifiers by default (`identifierPolicy: "strict"`). You can override this with `identifierPolicy: "off"` or provide custom text with `identifierPolicy: "custom"` and `identifierInstructions`.
 
+You can optionally specify a different model for compaction summarization via `agents.defaults.compaction.model`. This is useful when your primary model is a local or small model and you want compaction summaries produced by a more capable model. The override accepts any `provider/model-id` string:
+
+```json
+{
+  "agents": {
+    "defaults": {
+      "compaction": {
+        "model": "openrouter/anthropic/claude-sonnet-4-5"
+      }
+    }
+  }
+}
+```
+
+This also works with local models, for example a second Ollama model dedicated to summarization or a fine-tuned compaction specialist:
+
+```json
+{
+  "agents": {
+    "defaults": {
+      "compaction": {
+        "model": "ollama/llama3.1:8b"
+      }
+    }
+  }
+}
+```
+
+When unset, compaction uses the agent's primary model.
+
 ## Auto-compaction (default on)
 
 When a session nears or exceeds the model’s context window, OpenClaw triggers auto-compaction and may retry the original request using the compacted context.

src/agents/pi-embedded-runner/run/attempt.test.ts

@@ -639,6 +639,70 @@ describe("prependSystemPromptAddition", () => {
 });
 
 describe("buildAfterTurnLegacyCompactionParams", () => {
+  it("uses primary model when compaction.model is not set", () => {
+    const legacy = buildAfterTurnLegacyCompactionParams({
+      attempt: {
+        sessionKey: "agent:main:session:abc",
+        messageChannel: "slack",
+        messageProvider: "slack",
+        agentAccountId: "acct-1",
+        authProfileId: "openai:p1",
+        config: {} as OpenClawConfig,
+        skillsSnapshot: undefined,
+        senderIsOwner: true,
+        provider: "openai-codex",
+        modelId: "gpt-5.3-codex",
+        thinkLevel: "off",
+        reasoningLevel: "on",
+        extraSystemPrompt: "extra",
+        ownerNumbers: ["+15555550123"],
+      },
+      workspaceDir: "/tmp/workspace",
+      agentDir: "/tmp/agent",
+    });
+
+    expect(legacy).toMatchObject({
+      provider: "openai-codex",
+      model: "gpt-5.3-codex",
+    });
+  });
+
+  it("uses compaction.model override when set, splitting provider from model id", () => {
+    const legacy = buildAfterTurnLegacyCompactionParams({
+      attempt: {
+        sessionKey: "agent:main:session:abc",
+        messageChannel: "slack",
+        messageProvider: "slack",
+        agentAccountId: "acct-1",
+        authProfileId: "openai:p1",
+        config: {
+          agents: {
+            defaults: {
+              compaction: {
+                model: "openrouter/anthropic/claude-sonnet-4-5",
+              },
+            },
+          },
+        } as OpenClawConfig,
+        skillsSnapshot: undefined,
+        senderIsOwner: true,
+        provider: "openai-codex",
+        modelId: "gpt-5.3-codex",
+        thinkLevel: "off",
+        reasoningLevel: "on",
+        extraSystemPrompt: "extra",
+        ownerNumbers: ["+15555550123"],
+      },
+      workspaceDir: "/tmp/workspace",
+      agentDir: "/tmp/agent",
+    });
+
+    expect(legacy).toMatchObject({
+      provider: "openrouter",
+      model: "anthropic/claude-sonnet-4-5",
+    });
+  });
+
   it("includes resolved auth profile fields for context-engine afterTurn compaction", () => {
     const legacy = buildAfterTurnLegacyCompactionParams({
       attempt: {

src/agents/pi-embedded-runner/run/attempt.ts

@@ -659,6 +659,20 @@ export function buildAfterTurnLegacyCompactionParams(params: {
   workspaceDir: string;
   agentDir: string;
 }): Partial<CompactEmbeddedPiSessionParams> {
+  // Resolve compaction model: use config override or fall back to primary model
+  const compactionModelOverride = params.attempt.config?.agents?.defaults?.compaction?.model;
+  let compactionProvider = params.attempt.provider;
+  let compactionModelId = params.attempt.modelId;
+  if (compactionModelOverride) {
+    const slashIdx = compactionModelOverride.indexOf("/");
+    if (slashIdx > 0) {
+      compactionProvider = compactionModelOverride.slice(0, slashIdx);
+      compactionModelId = compactionModelOverride.slice(slashIdx + 1);
+    } else {
+      compactionModelId = compactionModelOverride;
+    }
+  }
+
   return {
     sessionKey: params.attempt.sessionKey,
     messageChannel: params.attempt.messageChannel,
@@ -670,8 +684,8 @@ export function buildAfterTurnLegacyCompactionParams(params: {
     config: params.attempt.config,
     skillsSnapshot: params.attempt.skillsSnapshot,
     senderIsOwner: params.attempt.senderIsOwner,
-    provider: params.attempt.provider,
-    model: params.attempt.modelId,
+    provider: compactionProvider,
+    model: compactionModelId,
     thinkLevel: params.attempt.thinkLevel,
     reasoningLevel: params.attempt.reasoningLevel,
     bashElevated: params.attempt.bashElevated,

src/config/types.agent-defaults.ts

@@ -322,6 +322,10 @@ export type AgentCompactionConfig = {
    * Set to [] to disable post-compaction context injection entirely.
    */
   postCompactionSections?: string[];
+  /** Optional model override for compaction summarization (e.g. "openrouter/anthropic/claude-sonnet-4-5").
+   * When set, compaction uses this model instead of the agent's primary model.
+   * Falls back to the primary model when unset. */
+  model?: string;
 };
 
 export type AgentCompactionMemoryFlushConfig = {

src/config/zod-schema.agent-defaults.ts

@@ -104,6 +104,7 @@ export const AgentDefaultsSchema = z
           .strict()
           .optional(),
         postCompactionSections: z.array(z.string()).optional(),
+        model: z.string().optional(),
         memoryFlush: z
           .object({
             enabled: z.boolean().optional(),