diff --git a/.changeset/fix-compaction-max-output-size.md b/.changeset/fix-compaction-max-output-size.md
new file mode 100644
index 0000000000..96aeb3431a
--- /dev/null
+++ b/.changeset/fix-compaction-max-output-size.md
@@ -0,0 +1,5 @@
+---
+"@moonshot-ai/kimi-code": patch
+---
+
+Fix compaction ignoring the configured max output size.
diff --git a/packages/agent-core/src/agent/compaction/full.ts b/packages/agent-core/src/agent/compaction/full.ts
index 2d608bae5b..e5f134df0e 100644
--- a/packages/agent-core/src/agent/compaction/full.ts
+++ b/packages/agent-core/src/agent/compaction/full.ts
@@ -264,6 +264,7 @@ export class FullCompaction {
       const provider = applyCompletionBudget({
         provider: this.agent.config.provider,
         budget: resolveCompletionBudget({
+          maxOutputSize: this.agent.config.maxOutputSize,
           reservedContextSize: this.agent.kimiConfig?.loopControl?.reservedContextSize,
         }),
         capability: this.agent.config.modelCapabilities,
diff --git a/packages/agent-core/test/agent/compaction/full.test.ts b/packages/agent-core/test/agent/compaction/full.test.ts
index d905354929..4e392908aa 100644
--- a/packages/agent-core/test/agent/compaction/full.test.ts
+++ b/packages/agent-core/test/agent/compaction/full.test.ts
@@ -16,6 +16,7 @@ import {
 } from '@moonshot-ai/kosong';
 import { afterEach, describe, expect, it, vi } from 'vitest';
 
+import type { KimiConfig } from '../../../src/config';
 import type { AgentOptions } from '../../../src/agent';
 import { DefaultCompactionStrategy, type CompactionStrategy } from '../../../src/agent/compaction';
 import { FLAG_DEFINITIONS, MASTER_ENV } from '../../../src/flags';
@@ -1770,6 +1771,46 @@ describe('FullCompaction', () => {
     expect(compactionMaxCompletionTokens).toEqual([undefined]);
   });
 
+  it('honors maxOutputSize from model config during compaction', async () => {
+    let callCount = 0;
+    const compactionMaxCompletionTokens: unknown[] = [];
+    const generate: GenerateFn = async (provider, _system, _tools, _history, callbacks) => {
+      callCount += 1;
+      if (callCount === 1) {
+        throw new APIContextOverflowError(400, 'Context length exceeded', 'req-max-output');
+      }
+      if (callCount === 2) {
+        compactionMaxCompletionTokens.push(providerMaxCompletionTokens(provider));
+        return textResult('Max output compacted summary.');
+      }
+      await callbacks?.onMessagePart?.({
+        type: 'text',
+        text: 'Recovered with max output.',
+      });
+      return textResult('Recovered with max output.');
+    };
+    const ctx = testAgent({ generate });
+    ctx.configure({
+      provider: CATALOGUED_PROVIDER,
+      modelCapabilities: CATALOGUED_MODEL_CAPABILITIES,
+    });
+    // Set maxOutputSize on the harness's internal kimiConfig — the
+    // compaction path reads it via ConfigState.maxOutputSize.
+    const models = (ctx as unknown as { kimiConfig: KimiConfig }).kimiConfig.models;
+    models![CATALOGUED_PROVIDER.model] = {
+      ...models![CATALOGUED_PROVIDER.model]!,
+      maxOutputSize: 384000,
+    };
+    ctx.appendExchange(1, 'old user one', 'old assistant one', 20);
+    ctx.newEvents();
+
+    await ctx.rpc.prompt({ input: [{ type: 'text', text: 'Retry with max output' }] });
+    await ctx.untilTurnEnd();
+
+    expect(callCount).toBe(3);
+    expect(compactionMaxCompletionTokens).toEqual([384000]);
+  });
+
   it('ignores filtered assistant placeholders when checking the retained overflow suffix', async () => {
     let callCount = 0;
     const generate: GenerateFn = async (_provider, _system, _tools, _history, callbacks) => {