diff --git a/packages/core/src/core/loggingContentGenerator.test.ts b/packages/core/src/core/loggingContentGenerator.test.ts
index dd354fa16f..45e5028553 100644
--- a/packages/core/src/core/loggingContentGenerator.test.ts
+++ b/packages/core/src/core/loggingContentGenerator.test.ts
@@ -32,6 +32,7 @@ import { LoggingContentGenerator } from './loggingContentGenerator.js';
 import type { Config } from '../config/config.js';
 import { UserTierId } from '../code_assist/types.js';
 import { ApiRequestEvent, LlmRole } from '../telemetry/types.js';
+import { FatalAuthenticationError } from '../utils/errors.js';
 
 describe('LoggingContentGenerator', () => {
   let wrapped: ContentGenerator;
@@ -137,6 +138,19 @@ describe('LoggingContentGenerator', () => {
       const errorEvent = vi.mocked(logApiError).mock.calls[0][1];
       expect(errorEvent.duration_ms).toBe(1000);
     });
+
+    describe('error type extraction', () => {
+      it('should extract error type correctly', async () => {
+        const req = { contents: [], model: 'm' };
+        const error = new FatalAuthenticationError('test');
+        vi.mocked(wrapped.generateContent).mockRejectedValue(error);
+        await expect(
+          loggingContentGenerator.generateContent(req, 'id', LlmRole.MAIN),
+        ).rejects.toThrow();
+        const errorEvent = vi.mocked(logApiError).mock.calls[0][1];
+        expect(errorEvent.error_type).toBe('FatalAuthenticationError');
+      });
+    });
   });
 
   describe('generateContentStream', () => {
diff --git a/packages/core/src/core/loggingContentGenerator.ts b/packages/core/src/core/loggingContentGenerator.ts
index 12a1722475..1544087ae0 100644
--- a/packages/core/src/core/loggingContentGenerator.ts
+++ b/packages/core/src/core/loggingContentGenerator.ts
@@ -36,6 +36,7 @@ import { toContents } from '../code_assist/converter.js';
 import { isStructuredError } from '../utils/quotaErrorDetection.js';
 import { runInDevTraceSpan, type SpanMetadata } from '../telemetry/trace.js';
 import { debugLogger } from '../utils/debugLogger.js';
+import { getErrorType } from '../utils/errors.js';
 
 interface StructuredError {
   status: number;
@@ -167,7 +168,7 @@ export class LoggingContentGenerator implements ContentGenerator {
     serverDetails?: ServerDetails,
   ): void {
     const errorMessage = error instanceof Error ? error.message : String(error);
-    const errorType = error instanceof Error ? error.name : 'unknown';
+    const errorType = getErrorType(error);
 
     logApiError(
       this.config,
diff --git a/packages/core/src/utils/errors.test.ts b/packages/core/src/utils/errors.test.ts
index 58c7004190..b3df89ef93 100644
--- a/packages/core/src/utils/errors.test.ts
+++ b/packages/core/src/utils/errors.test.ts
@@ -12,6 +12,14 @@ import {
   BadRequestError,
   ForbiddenError,
   getErrorMessage,
+  getErrorType,
+  FatalAuthenticationError,
+  FatalCancellationError,
+  FatalInputError,
+  FatalSandboxError,
+  FatalConfigError,
+  FatalTurnLimitedError,
+  FatalToolExecutionError,
 } from './errors.js';
 
 describe('getErrorMessage', () => {
@@ -201,3 +209,44 @@ describe('toFriendlyError', () => {
     expect(toFriendlyError(error)).toBe(error);
   });
 });
+
+describe('getErrorType', () => {
+  it('should return error name for standard errors', () => {
+    expect(getErrorType(new Error('test'))).toBe('Error');
+    expect(getErrorType(new TypeError('test'))).toBe('TypeError');
+    expect(getErrorType(new SyntaxError('test'))).toBe('SyntaxError');
+  });
+
+  it('should return constructor name for custom errors', () => {
+    expect(getErrorType(new FatalAuthenticationError('test'))).toBe(
+      'FatalAuthenticationError',
+    );
+    expect(getErrorType(new FatalInputError('test'))).toBe('FatalInputError');
+    expect(getErrorType(new FatalSandboxError('test'))).toBe(
+      'FatalSandboxError',
+    );
+    expect(getErrorType(new FatalConfigError('test'))).toBe('FatalConfigError');
+    expect(getErrorType(new FatalTurnLimitedError('test'))).toBe(
+      'FatalTurnLimitedError',
+    );
+    expect(getErrorType(new FatalToolExecutionError('test'))).toBe(
+      'FatalToolExecutionError',
+    );
+    expect(getErrorType(new FatalCancellationError('test'))).toBe(
+      'FatalCancellationError',
+    );
+    expect(getErrorType(new ForbiddenError('test'))).toBe('ForbiddenError');
+    expect(getErrorType(new UnauthorizedError('test'))).toBe(
+      'UnauthorizedError',
+    );
+    expect(getErrorType(new BadRequestError('test'))).toBe('BadRequestError');
+  });
+
+  it('should return "unknown" for non-Error objects', () => {
+    expect(getErrorType('string error')).toBe('unknown');
+    expect(getErrorType(123)).toBe('unknown');
+    expect(getErrorType({})).toBe('unknown');
+    expect(getErrorType(null)).toBe('unknown');
+    expect(getErrorType(undefined)).toBe('unknown');
+  });
+});
diff --git a/packages/core/src/utils/errors.ts b/packages/core/src/utils/errors.ts
index 2bba4f8abe..dc7d5b33c5 100644
--- a/packages/core/src/utils/errors.ts
+++ b/packages/core/src/utils/errors.ts
@@ -26,6 +26,15 @@ export function getErrorMessage(error: unknown): string {
   }
 }
 
+export function getErrorType(error: unknown): string {
+  if (!(error instanceof Error)) return 'unknown';
+
+  // Return constructor name if the generic 'Error' name is used (for custom errors)
+  return error.name === 'Error'
+    ? (error.constructor?.name ?? 'Error')
+    : error.name;
+}
+
 export class FatalError extends Error {
   constructor(
     message: string,