diff --git a/docs/cli/telemetry.md b/docs/cli/telemetry.md
index 2068759213..fec0fb41c3 100644
--- a/docs/cli/telemetry.md
+++ b/docs/cli/telemetry.md
@@ -306,6 +306,7 @@ Emitted at startup with the CLI configuration.
 - `extension_ids` (string)
 - `extensions_count` (int)
 - `auth_type` (string)
+- `worktree_active` (boolean)
 - `github_workflow_name` (string, optional)
 - `github_repository_hash` (string, optional)
 - `github_event_name` (string, optional)
diff --git a/packages/cli/src/test-utils/mockConfig.ts b/packages/cli/src/test-utils/mockConfig.ts
index d4f11212e3..e1505df970 100644
--- a/packages/cli/src/test-utils/mockConfig.ts
+++ b/packages/cli/src/test-utils/mockConfig.ts
@@ -44,6 +44,7 @@ export const createMockConfig = (overrides: Partial<Config> = {}): Config =>
     getDeleteSession: vi.fn(() => undefined),
     setSessionId: vi.fn(),
     getSessionId: vi.fn().mockReturnValue('mock-session-id'),
+    getWorktreeSettings: vi.fn(() => undefined),
     getContentGeneratorConfig: vi.fn(() => ({ authType: 'google' })),
     getAcpMode: vi.fn(() => false),
     isBrowserLaunchSuppressed: vi.fn(() => false),
diff --git a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
index 2f059030ca..11433db3e8 100644
--- a/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
+++ b/packages/core/src/telemetry/clearcut-logger/clearcut-logger.ts
@@ -687,6 +687,11 @@ export class ClearcutLogger {
         gemini_cli_key: EventMetadataKey.GEMINI_CLI_START_SESSION_EXTENSION_IDS,
         value: event.extension_ids.toString(),
       },
+      {
+        gemini_cli_key:
+          EventMetadataKey.GEMINI_CLI_START_SESSION_WORKTREE_ACTIVE,
+        value: event.worktree_active.toString(),
+      },
     ];
 
     // Add hardware information only to the start session event
diff --git a/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts b/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts
index 632730aeeb..b7b9c0fd3a 100644
--- a/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts
+++ b/packages/core/src/telemetry/clearcut-logger/event-metadata-key.ts
@@ -452,6 +452,9 @@ export enum EventMetadataKey {
   // Logs the name of extensions as a comma-separated string
   GEMINI_CLI_START_SESSION_EXTENSION_IDS = 120,
 
+  // Logs whether the session is running in a Git worktree.
+  GEMINI_CLI_START_SESSION_WORKTREE_ACTIVE = 191,
+
   // Logs the setting scope for an extension enablement.
   GEMINI_CLI_EXTENSION_ENABLE_SETTING_SCOPE = 102,
 
diff --git a/packages/core/src/telemetry/loggers.test.ts b/packages/core/src/telemetry/loggers.test.ts
index 4373a6b96c..27c23e7baa 100644
--- a/packages/core/src/telemetry/loggers.test.ts
+++ b/packages/core/src/telemetry/loggers.test.ts
@@ -195,48 +195,51 @@ describe('loggers', () => {
   });
 
   describe('logCliConfiguration', () => {
+    const baseMockConfig = {
+      getSessionId: () => 'test-session-id',
+      getModel: () => 'test-model',
+      getEmbeddingModel: () => 'test-embedding-model',
+      getSandbox: () => true,
+      getCoreTools: () => ['ls', 'read-file'],
+      getApprovalMode: () => 'default',
+      getContentGeneratorConfig: () => ({
+        model: 'test-model',
+        apiKey: 'test-api-key',
+        authType: AuthType.USE_VERTEX_AI,
+      }),
+      getTelemetryEnabled: () => true,
+      getUsageStatisticsEnabled: () => true,
+      getTelemetryLogPromptsEnabled: () => true,
+      getFileFilteringRespectGitIgnore: () => true,
+      getFileFilteringAllowBuildArtifacts: () => false,
+      getDebugMode: () => true,
+      getMcpServers: () => {
+        throw new Error('Should not call');
+      },
+      getQuestion: () => 'test-question',
+      getTargetDir: () => 'target-dir',
+      getProxy: () => 'http://test.proxy.com:8080',
+      getOutputFormat: () => OutputFormat.JSON,
+      getExtensions: () =>
+        [
+          { name: 'ext-one', id: 'id-one' },
+          { name: 'ext-two', id: 'id-two' },
+        ] as GeminiCLIExtension[],
+      getMcpClientManager: () => ({
+        getMcpServers: () => ({
+          'test-server': {
+            command: 'test-command',
+          },
+        }),
+      }),
+      isInteractive: () => false,
+      getExperiments: () => undefined,
+      getExperimentsAsync: async () => undefined,
+      getWorktreeSettings: () => undefined,
+    } as unknown as Config;
+
     it('should log the cli configuration', async () => {
-      const mockConfig = {
-        getSessionId: () => 'test-session-id',
-        getModel: () => 'test-model',
-        getEmbeddingModel: () => 'test-embedding-model',
-        getSandbox: () => true,
-        getCoreTools: () => ['ls', 'read-file'],
-        getApprovalMode: () => 'default',
-        getContentGeneratorConfig: () => ({
-          model: 'test-model',
-          apiKey: 'test-api-key',
-          authType: AuthType.USE_VERTEX_AI,
-        }),
-        getTelemetryEnabled: () => true,
-        getUsageStatisticsEnabled: () => true,
-        getTelemetryLogPromptsEnabled: () => true,
-        getFileFilteringRespectGitIgnore: () => true,
-        getFileFilteringAllowBuildArtifacts: () => false,
-        getDebugMode: () => true,
-        getMcpServers: () => {
-          throw new Error('Should not call');
-        },
-        getQuestion: () => 'test-question',
-        getTargetDir: () => 'target-dir',
-        getProxy: () => 'http://test.proxy.com:8080',
-        getOutputFormat: () => OutputFormat.JSON,
-        getExtensions: () =>
-          [
-            { name: 'ext-one', id: 'id-one' },
-            { name: 'ext-two', id: 'id-two' },
-          ] as GeminiCLIExtension[],
-        getMcpClientManager: () => ({
-          getMcpServers: () => ({
-            'test-server': {
-              command: 'test-command',
-            },
-          }),
-        }),
-        isInteractive: () => false,
-        getExperiments: () => undefined,
-        getExperimentsAsync: async () => undefined,
-      } as unknown as Config;
+      const mockConfig = baseMockConfig;
 
       const startSessionEvent = new StartSessionEvent(mockConfig);
       logCliConfiguration(mockConfig, startSessionEvent);
@@ -270,9 +273,32 @@ describe('loggers', () => {
           extensions_count: 2,
           extensions: 'ext-one,ext-two',
           auth_type: 'vertex-ai',
+          worktree_active: false,
         },
       });
     });
+
+    it('should set worktree_active to true when worktree settings are present', async () => {
+      const mockConfig = {
+        ...baseMockConfig,
+        getWorktreeSettings: () => ({
+          name: 'test-worktree',
+          path: '/path/to/worktree',
+          baseSha: 'test-sha',
+        }),
+      } as unknown as Config;
+
+      const startSessionEvent = new StartSessionEvent(mockConfig);
+      logCliConfiguration(mockConfig, startSessionEvent);
+
+      await new Promise(process.nextTick);
+      expect(mockLogger.emit).toHaveBeenCalledWith({
+        body: 'CLI configuration loaded.',
+        attributes: expect.objectContaining({
+          worktree_active: true,
+        }),
+      });
+    });
   });
 
   describe('logUserPrompt', () => {
diff --git a/packages/core/src/telemetry/types.ts b/packages/core/src/telemetry/types.ts
index 0ee6e63503..1e0e3abc6e 100644
--- a/packages/core/src/telemetry/types.ts
+++ b/packages/core/src/telemetry/types.ts
@@ -77,6 +77,7 @@ export class StartSessionEvent implements BaseTelemetryEvent {
   extensions: string;
   extension_ids: string;
   auth_type?: string;
+  worktree_active: boolean;
 
   constructor(config: Config, toolRegistry?: ToolRegistry) {
     const generatorConfig = config.getContentGeneratorConfig();
@@ -114,6 +115,7 @@ export class StartSessionEvent implements BaseTelemetryEvent {
     this.extensions = extensions.map((e) => e.name).join(',');
     this.extension_ids = extensions.map((e) => e.id).join(',');
     this.auth_type = generatorConfig?.authType;
+    this.worktree_active = !!config.getWorktreeSettings();
     if (toolRegistry) {
       const mcpTools = toolRegistry
         .getAllTools()
@@ -147,6 +149,7 @@ export class StartSessionEvent implements BaseTelemetryEvent {
       extensions_count: this.extensions_count,
       extension_ids: this.extension_ids,
       auth_type: this.auth_type,
+      worktree_active: this.worktree_active,
     };
   }