diff --git a/packages/core/src/code_assist/oauth2.test.ts b/packages/core/src/code_assist/oauth2.test.ts
index 7e3c38f0..4223bb75 100644
--- a/packages/core/src/code_assist/oauth2.test.ts
+++ b/packages/core/src/code_assist/oauth2.test.ts
@@ -64,6 +64,7 @@ describe('oauth2', () => {
       setCredentials: mockSetCredentials,
       getAccessToken: mockGetAccessToken,
       credentials: mockTokens,
+      on: vi.fn(),
     } as unknown as OAuth2Client;
     vi.mocked(OAuth2Client).mockImplementation(() => mockOAuth2Client);
 
@@ -136,10 +137,6 @@ describe('oauth2', () => {
     });
     expect(mockSetCredentials).toHaveBeenCalledWith(mockTokens);
 
-    const tokenPath = path.join(tempHomeDir, '.gemini', 'oauth_creds.json');
-    const tokenData = JSON.parse(fs.readFileSync(tokenPath, 'utf-8'));
-    expect(tokenData).toEqual(mockTokens);
-
     // Verify Google Account ID was cached
     const googleAccountIdPath = path.join(
       tempHomeDir,
diff --git a/packages/core/src/code_assist/oauth2.ts b/packages/core/src/code_assist/oauth2.ts
index d07c8560..a55f3804 100644
--- a/packages/core/src/code_assist/oauth2.ts
+++ b/packages/core/src/code_assist/oauth2.ts
@@ -58,6 +58,9 @@ export async function getOauthClient(): Promise<OAuth2Client> {
     clientId: OAUTH_CLIENT_ID,
     clientSecret: OAUTH_CLIENT_SECRET,
   });
+  client.on('tokens', async (tokens: Credentials) => {
+    await cacheCredentials(tokens);
+  });
 
   if (await loadCachedCredentials(client)) {
     // Found valid cached credentials.
@@ -130,8 +133,6 @@ async function authWithWeb(client: OAuth2Client): Promise<OauthWebLogin> {
             redirect_uri: redirectUri,
           });
           client.setCredentials(tokens);
-          await cacheCredentials(client.credentials);
-
           // Retrieve and cache Google Account ID during authentication
           try {
             const googleAccountId = await getGoogleAccountId(client);
diff --git a/packages/core/src/code_assist/server.test.ts b/packages/core/src/code_assist/server.test.ts
index d8d9c10a..9bcfa304 100644
--- a/packages/core/src/code_assist/server.test.ts
+++ b/packages/core/src/code_assist/server.test.ts
@@ -18,8 +18,8 @@ describe('CodeAssistServer', () => {
   });
 
   it('should call the generateContent endpoint', async () => {
-    const auth = new OAuth2Client();
-    const server = new CodeAssistServer(auth, 'test-project');
+    const client = new OAuth2Client();
+    const server = new CodeAssistServer(client, 'test-project');
     const mockResponse = {
       response: {
         candidates: [
@@ -53,8 +53,8 @@ describe('CodeAssistServer', () => {
   });
 
   it('should call the generateContentStream endpoint', async () => {
-    const auth = new OAuth2Client();
-    const server = new CodeAssistServer(auth, 'test-project');
+    const client = new OAuth2Client();
+    const server = new CodeAssistServer(client, 'test-project');
     const mockResponse = (async function* () {
       yield {
         response: {
@@ -90,8 +90,8 @@ describe('CodeAssistServer', () => {
   });
 
   it('should call the onboardUser endpoint', async () => {
-    const auth = new OAuth2Client();
-    const server = new CodeAssistServer(auth, 'test-project');
+    const client = new OAuth2Client();
+    const server = new CodeAssistServer(client, 'test-project');
     const mockResponse = {
       name: 'operations/123',
       done: true,
@@ -112,8 +112,8 @@ describe('CodeAssistServer', () => {
   });
 
   it('should call the loadCodeAssist endpoint', async () => {
-    const auth = new OAuth2Client();
-    const server = new CodeAssistServer(auth, 'test-project');
+    const client = new OAuth2Client();
+    const server = new CodeAssistServer(client, 'test-project');
     const mockResponse = {
       // TODO: Add mock response
     };
@@ -131,8 +131,8 @@ describe('CodeAssistServer', () => {
   });
 
   it('should return 0 for countTokens', async () => {
-    const auth = new OAuth2Client();
-    const server = new CodeAssistServer(auth, 'test-project');
+    const client = new OAuth2Client();
+    const server = new CodeAssistServer(client, 'test-project');
     const mockResponse = {
       totalTokens: 100,
     };
@@ -146,8 +146,8 @@ describe('CodeAssistServer', () => {
   });
 
   it('should throw an error for embedContent', async () => {
-    const auth = new OAuth2Client();
-    const server = new CodeAssistServer(auth, 'test-project');
+    const client = new OAuth2Client();
+    const server = new CodeAssistServer(client, 'test-project');
     await expect(
       server.embedContent({
         model: 'test-model',
diff --git a/packages/core/src/code_assist/server.ts b/packages/core/src/code_assist/server.ts
index 1eaf9217..8e74c8b2 100644
--- a/packages/core/src/code_assist/server.ts
+++ b/packages/core/src/code_assist/server.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { AuthClient } from 'google-auth-library';
+import { OAuth2Client } from 'google-auth-library';
 import {
   CodeAssistGlobalUserSettingResponse,
   LoadCodeAssistRequest,
@@ -46,7 +46,7 @@ export const CODE_ASSIST_API_VERSION = 'v1internal';
 
 export class CodeAssistServer implements ContentGenerator {
   constructor(
-    readonly auth: AuthClient,
+    readonly client: OAuth2Client,
     readonly projectId?: string,
     readonly httpOptions: HttpOptions = {},
   ) {}
@@ -129,7 +129,7 @@ export class CodeAssistServer implements ContentGenerator {
     req: object,
     signal?: AbortSignal,
   ): Promise<T> {
-    const res = await this.auth.request({
+    const res = await this.client.request({
       url: `${CODE_ASSIST_ENDPOINT}/${CODE_ASSIST_API_VERSION}:${method}`,
       method: 'POST',
       headers: {
@@ -144,7 +144,7 @@ export class CodeAssistServer implements ContentGenerator {
   }
 
   async getEndpoint<T>(method: string, signal?: AbortSignal): Promise<T> {
-    const res = await this.auth.request({
+    const res = await this.client.request({
       url: `${CODE_ASSIST_ENDPOINT}/${CODE_ASSIST_API_VERSION}:${method}`,
       method: 'GET',
       headers: {
@@ -162,7 +162,7 @@ export class CodeAssistServer implements ContentGenerator {
     req: object,
     signal?: AbortSignal,
   ): Promise<AsyncGenerator<T>> {
-    const res = await this.auth.request({
+    const res = await this.client.request({
       url: `${CODE_ASSIST_ENDPOINT}/${CODE_ASSIST_API_VERSION}:${method}`,
       method: 'POST',
       params: {
diff --git a/packages/core/src/code_assist/setup.ts b/packages/core/src/code_assist/setup.ts
index f0ea60b3..7db6bdcd 100644
--- a/packages/core/src/code_assist/setup.ts
+++ b/packages/core/src/code_assist/setup.ts
@@ -27,9 +27,9 @@ export class ProjectIdRequiredError extends Error {
  * @param projectId the user's project id, if any
  * @returns the user's actual project id
  */
-export async function setupUser(authClient: OAuth2Client): Promise<string> {
+export async function setupUser(client: OAuth2Client): Promise<string> {
   let projectId = process.env.GOOGLE_CLOUD_PROJECT;
-  const caServer = new CodeAssistServer(authClient, projectId);
+  const caServer = new CodeAssistServer(client, projectId);
 
   const clientMetadata: ClientMetadata = {
     ideType: 'IDE_UNSPECIFIED',