diff --git a/packages/cli/src/utils/activityLogger.test.ts b/packages/cli/src/utils/activityLogger.test.ts
index e80eff6485..9d73c0d19f 100644
--- a/packages/cli/src/utils/activityLogger.test.ts
+++ b/packages/cli/src/utils/activityLogger.test.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { describe, it, expect, beforeEach } from 'vitest';
+import { describe, it, expect, beforeEach, vi } from 'vitest';
 import { ActivityLogger, type NetworkLog } from './activityLogger.js';
 import type { ConsoleLogPayload } from '@google/gemini-cli-core';
 
@@ -132,4 +132,95 @@ describe('ActivityLogger', () => {
     expect(after.console.length).toBe(0);
     expect(after.network.length).toBe(0);
   });
+
+  it('preserves headers and method from Request object when intercepting fetch', async () => {
+    const originalFetch = global.fetch;
+
+    const mockFetch = vi.fn().mockImplementation(() =>
+      Promise.resolve({
+        status: 200,
+        headers: new Headers(),
+        body: null,
+        clone: () => ({
+          body: null,
+          status: 200,
+          headers: new Headers(),
+          text: async () => 'ok',
+          json: async () => ({}),
+        }),
+      } as unknown as Response),
+    );
+
+    global.fetch = mockFetch;
+
+    try {
+      // @ts-expect-error - accessing private property for testing
+      logger.isInterceptionEnabled = false;
+      logger.enable();
+
+      const request = new Request('https://api.example.com/data', {
+        headers: { Authorization: 'Bearer test-token' },
+        method: 'POST',
+      });
+
+      await global.fetch(request);
+
+      expect(mockFetch).toHaveBeenCalled();
+      const [, calledInit] = mockFetch.mock.calls[0];
+
+      expect(calledInit?.headers).toBeDefined();
+      const headers = new Headers(calledInit?.headers as HeadersInit);
+      expect(headers.get('Authorization')).toBe('Bearer test-token');
+      expect(headers.has('x-activity-request-id')).toBe(true);
+      expect(calledInit?.method).toBe('POST');
+    } finally {
+      global.fetch = originalFetch;
+      // @ts-expect-error - reset private property
+      logger.isInterceptionEnabled = false;
+    }
+  });
+
+  it('replaces Request headers with init headers (Fetch spec compliance)', async () => {
+    const originalFetch = global.fetch;
+    const mockFetch = vi.fn().mockImplementation(() =>
+      Promise.resolve({
+        status: 200,
+        headers: new Headers(),
+        body: null,
+        clone: () => ({
+          body: null,
+          status: 200,
+          headers: new Headers(),
+          text: async () => 'ok',
+        }),
+      } as unknown as Response),
+    );
+    global.fetch = mockFetch;
+
+    try {
+      // @ts-expect-error - accessing private property for testing
+      logger.isInterceptionEnabled = false;
+      logger.enable();
+
+      const request = new Request('https://api.example.com/data', {
+        headers: { 'X-Old': 'old-value', 'X-Shared': 'old-shared' },
+      });
+
+      await global.fetch(request, {
+        headers: { 'X-New': 'new-value', 'X-Shared': 'new-shared' },
+      });
+
+      const [, calledInit] = mockFetch.mock.calls[0];
+      const headers = new Headers(calledInit?.headers as HeadersInit);
+
+      expect(headers.get('X-New')).toBe('new-value');
+      expect(headers.get('X-Shared')).toBe('new-shared');
+      expect(headers.has('X-Old')).toBe(false);
+      expect(headers.has('x-activity-request-id')).toBe(true);
+    } finally {
+      global.fetch = originalFetch;
+      // @ts-expect-error - reset private property
+      logger.isInterceptionEnabled = false;
+    }
+  });
 });
diff --git a/packages/cli/src/utils/activityLogger.ts b/packages/cli/src/utils/activityLogger.ts
index 8118ccdde9..8f47b39808 100644
--- a/packages/cli/src/utils/activityLogger.ts
+++ b/packages/cli/src/utils/activityLogger.ts
@@ -302,18 +302,31 @@ export class ActivityLogger extends EventEmitter {
         return originalFetch(input, init);
 
       const id = Math.random().toString(36).substring(7);
-      const method = (init?.method || 'GET').toUpperCase();
 
-      const newInit = { ...init };
-      const headers = new Headers(init?.headers || {});
+      const inputMethod =
+        typeof input === 'object' && 'method' in input
+          ? input.method
+          : undefined;
+      const inputHeaders =
+        typeof input === 'object' && 'headers' in input
+          ? input.headers
+          : undefined;
+
+      const method = (init?.method ?? inputMethod ?? 'GET').toUpperCase();
+      const headers = new Headers(init?.headers ?? inputHeaders ?? {});
       headers.set(ACTIVITY_ID_HEADER, id);
-      newInit.headers = headers;
+
+      const newInit = {
+        ...init,
+        method,
+        headers,
+      };
 
       let reqBody = '';
-      if (init?.body) {
-        if (typeof init.body === 'string') reqBody = init.body;
-        else if (init.body instanceof URLSearchParams)
-          reqBody = init.body.toString();
+      const body = newInit.body;
+      if (body) {
+        if (typeof body === 'string') reqBody = body;
+        else if (body instanceof URLSearchParams) reqBody = body.toString();
       }
 
       this.requestStartTimes.set(id, Date.now());