diff --git a/packages/core/src/utils/errorParsing.test.ts b/packages/core/src/utils/errorParsing.test.ts
index 291145d2e8b..b84259e8e45 100644
--- a/packages/core/src/utils/errorParsing.test.ts
+++ b/packages/core/src/utils/errorParsing.test.ts
@@ -114,4 +114,20 @@ describe('parseAndFormatApiError', () => {
     const expected = '[API Error: An unknown error occurred.]';
     expect(parseAndFormatApiError(error)).toBe(expected);
   });
+
+  it('should decode and format a byte-array encoded error message', () => {
+    const json = JSON.stringify({
+      error: {
+        code: 429,
+        message: 'No capacity available',
+        status: 'RESOURCE_EXHAUSTED',
+      },
+    });
+    const byteString = Array.from(json)
+      .map((c) => c.charCodeAt(0))
+      .join(',');
+    const result = parseAndFormatApiError(byteString);
+    expect(result).toContain('[API Error: No capacity available');
+    expect(result).toContain('RESOURCE_EXHAUSTED');
+  });
 });
diff --git a/packages/core/src/utils/errorParsing.ts b/packages/core/src/utils/errorParsing.ts
index bad61ea9e24..64c7c6c285f 100644
--- a/packages/core/src/utils/errorParsing.ts
+++ b/packages/core/src/utils/errorParsing.ts
@@ -9,6 +9,18 @@ import { DEFAULT_GEMINI_FLASH_MODEL } from '../config/models.js';
 import type { UserTierId } from '../code_assist/types.js';
 import { AuthType } from '../core/contentGenerator.js';
 
+function tryDecodeByteArray(s: string): string | null {
+  if (!/^\d+(,\d+)+$/.test(s)) {
+    return null;
+  }
+  try {
+    const bytes = new Uint8Array(s.split(',').map(Number));
+    return new TextDecoder().decode(bytes);
+  } catch {
+    return null;
+  }
+}
+
 const RATE_LIMIT_ERROR_MESSAGE_USE_GEMINI =
   '\nPlease wait and try again later. To increase your limits, request a quota increase through AI Studio, or switch to another /auth method';
 const RATE_LIMIT_ERROR_MESSAGE_VERTEX =
@@ -40,6 +52,16 @@ export function parseAndFormatApiError(
   fallbackModel?: string,
 ): string {
   if (isStructuredError(error)) {
+    const decoded = tryDecodeByteArray(error.message);
+    if (decoded) {
+      return parseAndFormatApiError(
+        decoded,
+        authType,
+        userTier,
+        currentModel,
+        fallbackModel,
+      );
+    }
     let text = `[API Error: ${error.message}]`;
     if (error.status === 429) {
       text += getRateLimitMessage(authType, fallbackModel);
@@ -49,9 +71,19 @@ export function parseAndFormatApiError(
 
   // The error message might be a string containing a JSON object.
   if (typeof error === 'string') {
+    const decoded = tryDecodeByteArray(error);
+    if (decoded) {
+      return parseAndFormatApiError(
+        decoded,
+        authType,
+        userTier,
+        currentModel,
+        fallbackModel,
+      );
+    }
     const jsonStart = error.indexOf('{');
     if (jsonStart === -1) {
-      return `[API Error: ${error}]`; // Not a JSON error, return as is.
+      return `[API Error: ${error}]`;
     }
 
     const jsonString = error.substring(jsonStart);