diff --git a/packages/core/src/utils/googleQuotaErrors.test.ts b/packages/core/src/utils/googleQuotaErrors.test.ts
index cd09e53511..90769def35 100644
--- a/packages/core/src/utils/googleQuotaErrors.test.ts
+++ b/packages/core/src/utils/googleQuotaErrors.test.ts
@@ -134,21 +134,21 @@ describe('classifyGoogleError', () => {
     expect((result as TerminalQuotaError).cause).toBe(apiError);
   });
 
-  it('should return RetryableQuotaError for long retry delays', () => {
+  it('should return TerminalQuotaError for retry delays over 5 minutes', () => {
     const apiError: GoogleApiError = {
       code: 429,
       message: 'Too many requests',
       details: [
         {
           '@type': 'type.googleapis.com/google.rpc.RetryInfo',
-          retryDelay: '301s', // Any delay is now retryable
+          retryDelay: '301s', // Over 5 min threshold => terminal
         },
       ],
     };
     vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
     const result = classifyGoogleError(new Error());
-    expect(result).toBeInstanceOf(RetryableQuotaError);
-    expect((result as RetryableQuotaError).retryDelayMs).toBe(301000);
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+    expect((result as TerminalQuotaError).retryDelayMs).toBe(301000);
   });
 
   it('should return RetryableQuotaError for short retry delays', () => {
@@ -285,6 +285,34 @@ describe('classifyGoogleError', () => {
     );
   });
 
+  it('should return TerminalQuotaError for Cloud Code RATE_LIMIT_EXCEEDED with retry delay over 5 minutes', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message:
+        'You have exhausted your capacity on this model. Your quota will reset after 10m.',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.ErrorInfo',
+          reason: 'RATE_LIMIT_EXCEEDED',
+          domain: 'cloudcode-pa.googleapis.com',
+          metadata: {
+            uiMessage: 'true',
+            model: 'gemini-2.5-pro',
+          },
+        },
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: '600s',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(new Error());
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+    expect((result as TerminalQuotaError).retryDelayMs).toBe(600000);
+    expect((result as TerminalQuotaError).reason).toBe('RATE_LIMIT_EXCEEDED');
+  });
+
   it('should return TerminalQuotaError for Cloud Code QUOTA_EXHAUSTED', () => {
     const apiError: GoogleApiError = {
       code: 429,
@@ -427,6 +455,40 @@ describe('classifyGoogleError', () => {
     }
   });
 
+  it('should return TerminalQuotaError when fallback "Please retry in" delay exceeds 5 minutes', () => {
+    const errorWithEmptyDetails = {
+      error: {
+        code: 429,
+        message: 'Resource exhausted. Please retry in 400s',
+        details: [],
+      },
+    };
+
+    const result = classifyGoogleError(errorWithEmptyDetails);
+
+    expect(result).toBeInstanceOf(TerminalQuotaError);
+    if (result instanceof TerminalQuotaError) {
+      expect(result.retryDelayMs).toBe(400000);
+    }
+  });
+
+  it('should return RetryableQuotaError when retry delay is exactly 5 minutes', () => {
+    const apiError: GoogleApiError = {
+      code: 429,
+      message: 'Too many requests',
+      details: [
+        {
+          '@type': 'type.googleapis.com/google.rpc.RetryInfo',
+          retryDelay: '300s',
+        },
+      ],
+    };
+    vi.spyOn(errorParser, 'parseGoogleApiError').mockReturnValue(apiError);
+    const result = classifyGoogleError(new Error());
+    expect(result).toBeInstanceOf(RetryableQuotaError);
+    expect((result as RetryableQuotaError).retryDelayMs).toBe(300000);
+  });
+
   it('should return RetryableQuotaError without delay time for generic 429 without specific message', () => {
     const generic429 = {
       status: 429,
diff --git a/packages/core/src/utils/googleQuotaErrors.ts b/packages/core/src/utils/googleQuotaErrors.ts
index fac291f36e..5a0bf48092 100644
--- a/packages/core/src/utils/googleQuotaErrors.ts
+++ b/packages/core/src/utils/googleQuotaErrors.ts
@@ -100,6 +100,13 @@ function parseDurationInSeconds(duration: string): number | null {
   return null;
 }
 
+/**
+ * Maximum retry delay (in seconds) before a retryable error is treated as terminal.
+ * If the server suggests waiting longer than this, the user is effectively locked out,
+ * so we trigger the fallback/credits flow instead of silently waiting.
+ */
+const MAX_RETRYABLE_DELAY_SECONDS = 300; // 5 minutes
+
 /**
  * Valid Cloud Code API domains for VALIDATION_REQUIRED errors.
  */
@@ -248,15 +255,15 @@ export function classifyGoogleError(error: unknown): unknown {
     if (match?.[1]) {
       const retryDelaySeconds = parseDurationInSeconds(match[1]);
       if (retryDelaySeconds !== null) {
-        return new RetryableQuotaError(
-          errorMessage,
-          googleApiError ?? {
-            code: status ?? 429,
-            message: errorMessage,
-            details: [],
-          },
-          retryDelaySeconds,
-        );
+        const cause = googleApiError ?? {
+          code: status ?? 429,
+          message: errorMessage,
+          details: [],
+        };
+        if (retryDelaySeconds > MAX_RETRYABLE_DELAY_SECONDS) {
+          return new TerminalQuotaError(errorMessage, cause, retryDelaySeconds);
+        }
+        return new RetryableQuotaError(errorMessage, cause, retryDelaySeconds);
       }
     } else if (status === 429 || status === 499) {
       // Fallback: If it is a 429 or 499 but doesn't have a specific "retry in" message,
@@ -325,10 +332,19 @@ export function classifyGoogleError(error: unknown): unknown {
     if (errorInfo.domain) {
       if (isCloudCodeDomain(errorInfo.domain)) {
         if (errorInfo.reason === 'RATE_LIMIT_EXCEEDED') {
+          const effectiveDelay = delaySeconds ?? 10;
+          if (effectiveDelay > MAX_RETRYABLE_DELAY_SECONDS) {
+            return new TerminalQuotaError(
+              `${googleApiError.message}`,
+              googleApiError,
+              effectiveDelay,
+              errorInfo.reason,
+            );
+          }
           return new RetryableQuotaError(
             `${googleApiError.message}`,
             googleApiError,
-            delaySeconds ?? 10,
+            effectiveDelay,
           );
         }
         if (errorInfo.reason === 'QUOTA_EXHAUSTED') {
@@ -345,6 +361,13 @@ export function classifyGoogleError(error: unknown): unknown {
 
   // 2. Check for delays in RetryInfo
   if (retryInfo?.retryDelay && delaySeconds) {
+    if (delaySeconds > MAX_RETRYABLE_DELAY_SECONDS) {
+      return new TerminalQuotaError(
+        `${googleApiError.message}\nSuggested retry after ${retryInfo.retryDelay}.`,
+        googleApiError,
+        delaySeconds,
+      );
+    }
     return new RetryableQuotaError(
       `${googleApiError.message}\nSuggested retry after ${retryInfo.retryDelay}.`,
       googleApiError,