diff --git a/extensions/google/cli-backend.ts b/extensions/google/cli-backend.ts
index 9a3249ace39c..41593706147d 100644
--- a/extensions/google/cli-backend.ts
+++ b/extensions/google/cli-backend.ts
@@ -28,6 +28,7 @@ const GEMINI_CLI_API_KEY_AUTH_ENV = [
   "GOOGLE_API_KEY",
   "GOOGLE_CLOUD_PROJECT",
   "GOOGLE_CLOUD_PROJECT_ID",
+  "GOOGLE_CLOUD_QUOTA_PROJECT",
   "GOOGLE_CLOUD_LOCATION",
   "GOOGLE_GEMINI_BASE_URL",
   "GEMINI_CLI_CUSTOM_HEADERS",
@@ -54,6 +55,7 @@ type GeminiAuthProfileCredential = {
   refresh?: string;
   expires?: number;
   idToken?: string;
+  projectId?: string;
 };
 
 type GeminiOAuthCredential = GeminiAuthProfileCredential & {
@@ -118,6 +120,7 @@ function requireGeminiOAuthCredential(
     refresh,
     expires: credential.expires,
     idToken: normalizeString(credential.idToken),
+    projectId: normalizeString(credential.projectId),
   };
 }
 
@@ -197,6 +200,18 @@ async function clearGeminiCliCachedCredentials(geminiDir: string): Promise<void>
   await fs.rm(path.join(geminiDir, GEMINI_CLI_CREDENTIALS_FILENAME), { force: true });
 }
 
+function buildGeminiCliProjectEnv(projectId: string | undefined): Record<string, string> {
+  const normalized = normalizeString(projectId);
+  if (!normalized) {
+    return {};
+  }
+  return {
+    GOOGLE_CLOUD_PROJECT: normalized,
+    GOOGLE_CLOUD_PROJECT_ID: normalized,
+    GOOGLE_CLOUD_QUOTA_PROJECT: normalized,
+  };
+}
+
 async function prepareGeminiCliOAuthHome(
   ctx: GeminiCliAuthHomeContext,
   credential: GeminiAuthProfileCredential | undefined,
@@ -227,6 +242,7 @@ async function prepareGeminiCliOAuthHome(
     env: {
       GEMINI_CLI_HOME: home,
       GEMINI_FORCE_FILE_STORAGE: "true",
+      ...buildGeminiCliProjectEnv(oauth.projectId),
     },
     clearEnv: [...GEMINI_CLI_PROFILE_AUTH_ENV],
   };
diff --git a/extensions/google/setup-api.test.ts b/extensions/google/setup-api.test.ts
index ac99631f63d7..c55b4c696472 100644
--- a/extensions/google/setup-api.test.ts
+++ b/extensions/google/setup-api.test.ts
@@ -17,6 +17,7 @@ type GeminiPrepareContext = Parameters<
     refresh?: string;
     expires?: number;
     idToken?: string;
+    projectId?: string;
     key?: string;
     email?: string;
   };
@@ -38,6 +39,7 @@ function buildGeminiOAuthPrepareContext(workspaceDir: string): GeminiPrepareCont
       refresh: "refresh-token",
       expires: 1_800_000_000_000,
       idToken: "id-token",
+      projectId: "profile-project",
       email: "user@example.test",
     },
   };
@@ -101,6 +103,9 @@ describe("google gemini cli backend auth bridge", () => {
       home = prepared?.env?.GEMINI_CLI_HOME;
       expect(home).toBeTruthy();
       expect(prepared?.env?.GEMINI_FORCE_FILE_STORAGE).toBe("true");
+      expect(prepared?.env?.GOOGLE_CLOUD_PROJECT).toBe("profile-project");
+      expect(prepared?.env?.GOOGLE_CLOUD_PROJECT_ID).toBe("profile-project");
+      expect(prepared?.env?.GOOGLE_CLOUD_QUOTA_PROJECT).toBe("profile-project");
       expect(home).toContain(path.join(context.agentDir, "cli-runtimes", "google-gemini-cli"));
       expect(home).not.toContain("user@example.test");
 
@@ -214,6 +219,7 @@ describe("google gemini cli backend auth bridge", () => {
     const originalForceEncryptedFileStorage = process.env.GEMINI_FORCE_ENCRYPTED_FILE_STORAGE;
     const originalGeminiApiKey = process.env.GEMINI_API_KEY;
     const originalGoogleApiKey = process.env.GOOGLE_API_KEY;
+    const originalQuotaProject = process.env.GOOGLE_CLOUD_QUOTA_PROJECT;
     let prepared:
       | Awaited<ReturnType<NonNullable<typeof backend.prepareExecution>>>
       | null
@@ -224,6 +230,7 @@ describe("google gemini cli backend auth bridge", () => {
     process.env.GEMINI_FORCE_ENCRYPTED_FILE_STORAGE = "true";
     process.env.GEMINI_API_KEY = "ambient-gemini-key";
     process.env.GOOGLE_API_KEY = "ambient-google-key";
+    process.env.GOOGLE_CLOUD_QUOTA_PROJECT = "ambient-project";
 
     try {
       prepared = await backend.prepareExecution?.(buildGeminiOAuthPrepareContext(workspaceDir));
@@ -238,6 +245,7 @@ describe("google gemini cli backend auth bridge", () => {
         "GOOGLE_API_KEY",
         "GOOGLE_CLOUD_PROJECT",
         "GOOGLE_CLOUD_PROJECT_ID",
+        "GOOGLE_CLOUD_QUOTA_PROJECT",
         "GOOGLE_CLOUD_LOCATION",
         "GOOGLE_GEMINI_BASE_URL",
         "GEMINI_CLI_CUSTOM_HEADERS",
@@ -250,6 +258,7 @@ describe("google gemini cli backend auth bridge", () => {
       restoreEnv("GEMINI_FORCE_ENCRYPTED_FILE_STORAGE", originalForceEncryptedFileStorage);
       restoreEnv("GEMINI_API_KEY", originalGeminiApiKey);
       restoreEnv("GOOGLE_API_KEY", originalGoogleApiKey);
+      restoreEnv("GOOGLE_CLOUD_QUOTA_PROJECT", originalQuotaProject);
       await prepared?.cleanup?.();
       await fs.rm(workspaceDir, { recursive: true, force: true });
     }