diff --git a/src/__tests__/summarize.test.ts b/src/__tests__/summarize.test.ts
index cc7ceeb..2da9779 100644
--- a/src/__tests__/summarize.test.ts
+++ b/src/__tests__/summarize.test.ts
@@ -38,13 +38,13 @@ const mockProvider = {
 beforeEach(() => {
   vi.clearAllMocks();
   mockGetProvider.mockReturnValue(mockProvider);
-  mockLoadGlobalConfig.mockReturnValue({
-    language: 'ja',
-    defaultPiece: 'default',
-    logLevel: 'info',
-    provider: 'claude',
-    model: 'haiku',
-  });
+  mockLoadGlobalConfig.mockReturnValue({
+    language: 'ja',
+    defaultPiece: 'default',
+    logLevel: 'info',
+    provider: 'claude',
+    model: undefined,
+  });
 });
 
 describe('summarizeTaskName', () => {
@@ -63,16 +63,15 @@ describe('summarizeTaskName', () => {
     // Then
     expect(result).toBe('add-auth');
     expect(mockGetProvider).toHaveBeenCalledWith('claude');
-    expect(mockProviderCall).toHaveBeenCalledWith(
-      'summarizer',
-      'long task name for testing',
-      expect.objectContaining({
-        cwd: '/project',
-        model: 'haiku',
-        allowedTools: [],
-      })
-    );
-  });
+    expect(mockProviderCall).toHaveBeenCalledWith(
+      'summarizer',
+      'long task name for testing',
+      expect.objectContaining({
+        cwd: '/project',
+        allowedTools: [],
+      })
+    );
+  });
 
   it('should return AI-generated slug for English task name', async () => {
     // Given
diff --git a/src/infra/task/summarize.ts b/src/infra/task/summarize.ts
index fc704b4..15c5215 100644
--- a/src/infra/task/summarize.ts
+++ b/src/infra/task/summarize.ts
@@ -64,15 +64,18 @@ export class TaskSummarizer {
 
     const globalConfig = loadGlobalConfig();
     const providerType = (globalConfig.provider as ProviderType) ?? 'claude';
-    const model = options.model ?? globalConfig.model ?? 'haiku';
+    const model = options.model ?? globalConfig.model;
 
     const provider = getProvider(providerType);
-    const response = await provider.call('summarizer', taskName, {
+    const callOptions: SummarizeOptions & { systemPrompt: string; allowedTools: [] } = {
       cwd: options.cwd,
-      model,
       systemPrompt: loadTemplate('score_slug_system_prompt', 'en'),
       allowedTools: [],
-    });
+    };
+    if (model) {
+      callOptions.model = model;
+    }
+    const response = await provider.call('summarizer', taskName, callOptions);
 
     const slug = sanitizeSlug(response.content);
     log.info('Task name summarized', { original: taskName, slug });