diff --git a/packages/core/src/telemetry/sdk.test.ts b/packages/core/src/telemetry/sdk.test.ts
index d25bd688e3d..90b7a98ff37 100644
--- a/packages/core/src/telemetry/sdk.test.ts
+++ b/packages/core/src/telemetry/sdk.test.ts
@@ -24,6 +24,11 @@ import { TelemetryTarget } from './index.js';
 
 import * as os from 'node:os';
 import * as path from 'node:path';
+import { promises as fs } from 'node:fs';
+import {
+  resetDebugLoggingState,
+  setDebugLogSession,
+} from '../utils/debugLogger.js';
 
 vi.mock('@opentelemetry/exporter-trace-otlp-grpc');
 vi.mock('@opentelemetry/exporter-logs-otlp-grpc');
@@ -143,6 +148,77 @@ describe('Telemetry SDK', () => {
     );
   });
 
+  it('should route OpenTelemetry diagnostics to debug log instead of console output', async () => {
+    const consoleErrorSpy = vi
+      .spyOn(console, 'error')
+      .mockImplementation(() => {});
+    const consoleWarnSpy = vi
+      .spyOn(console, 'warn')
+      .mockImplementation(() => {});
+    const mkdirSpy = vi.spyOn(fs, 'mkdir').mockResolvedValue(undefined);
+    const appendFileSpy = vi
+      .spyOn(fs, 'appendFile')
+      .mockResolvedValue(undefined);
+    const unlinkSpy = vi.spyOn(fs, 'unlink').mockResolvedValue(undefined);
+    const symlinkSpy = vi.spyOn(fs, 'symlink').mockResolvedValue(undefined);
+    const previousDebugLogFileEnv = process.env['QWEN_DEBUG_LOG_FILE'];
+    try {
+      process.env['QWEN_DEBUG_LOG_FILE'] = '1';
+      setDebugLogSession({ getSessionId: () => 'otel-diag-test-session' });
+
+      diag.error(
+        JSON.stringify({
+          message:
+            'Error: PeriodicExportingMetricReader: metrics export failed (error Error: connect ECONNREFUSED)',
+        }),
+      );
+
+      diag.error('A different OpenTelemetry diagnostic');
+      diag.warn('An OpenTelemetry warning');
+
+      await vi.waitFor(() => {
+        expect(appendFileSpy).toHaveBeenCalledTimes(3);
+      });
+
+      expect(consoleErrorSpy).not.toHaveBeenCalled();
+      expect(consoleWarnSpy).not.toHaveBeenCalled();
+      expect(mkdirSpy).toHaveBeenCalled();
+      expect(appendFileSpy).toHaveBeenCalledWith(
+        expect.stringContaining('otel-diag-test-session'),
+        expect.stringContaining(
+          '[ERROR] [OTEL] {"message":"Error: PeriodicExportingMetricReader: metrics export failed (error Error: connect ECONNREFUSED)"}',
+        ),
+        'utf8',
+      );
+      expect(appendFileSpy).toHaveBeenCalledWith(
+        expect.stringContaining('otel-diag-test-session'),
+        expect.stringContaining(
+          '[ERROR] [OTEL] A different OpenTelemetry diagnostic',
+        ),
+        'utf8',
+      );
+      expect(appendFileSpy).toHaveBeenCalledWith(
+        expect.stringContaining('otel-diag-test-session'),
+        expect.stringContaining('[WARN] [OTEL] An OpenTelemetry warning'),
+        'utf8',
+      );
+    } finally {
+      consoleErrorSpy.mockRestore();
+      consoleWarnSpy.mockRestore();
+      mkdirSpy.mockRestore();
+      appendFileSpy.mockRestore();
+      unlinkSpy.mockRestore();
+      symlinkSpy.mockRestore();
+      setDebugLogSession(null);
+      resetDebugLoggingState();
+      if (previousDebugLogFileEnv === undefined) {
+        delete process.env['QWEN_DEBUG_LOG_FILE'];
+      } else {
+        process.env['QWEN_DEBUG_LOG_FILE'] = previousDebugLogFileEnv;
+      }
+    }
+  });
+
   it('should use HTTP exporters with signal-specific paths when protocol is http', () => {
     vi.spyOn(mockConfig, 'getTelemetryEnabled').mockReturnValue(true);
     vi.spyOn(mockConfig, 'getTelemetryOtlpProtocol').mockReturnValue('http');
diff --git a/packages/core/src/telemetry/sdk.ts b/packages/core/src/telemetry/sdk.ts
index 74c26b31754..4c47a02f2c0 100644
--- a/packages/core/src/telemetry/sdk.ts
+++ b/packages/core/src/telemetry/sdk.ts
@@ -4,7 +4,8 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { DiagConsoleLogger, DiagLogLevel, diag } from '@opentelemetry/api';
+import { DiagLogLevel, diag } from '@opentelemetry/api';
+import type { DiagLogger } from '@opentelemetry/api';
 import { OTLPTraceExporter } from '@opentelemetry/exporter-trace-otlp-grpc';
 import { OTLPLogExporter } from '@opentelemetry/exporter-logs-otlp-grpc';
 import { OTLPMetricExporter } from '@opentelemetry/exporter-metrics-otlp-grpc';
@@ -30,8 +31,21 @@ import {
 import { createDebugLogger } from '../utils/debugLogger.js';
 import { LogToSpanProcessor } from './log-to-span-processor.js';
 
-// For troubleshooting, set the log level to DiagLogLevel.DEBUG
-diag.setLogger(new DiagConsoleLogger(), DiagLogLevel.WARN);
+function createTelemetryDiagLogger(): DiagLogger {
+  const debugLogger = createDebugLogger('OTEL');
+  return {
+    error: (message, ...args) => debugLogger.error(message, ...args),
+    warn: (message, ...args) => debugLogger.warn(message, ...args),
+    info: (message, ...args) => debugLogger.info(message, ...args),
+    debug: (message, ...args) => debugLogger.debug(message, ...args),
+    verbose: (message, ...args) => debugLogger.debug(message, ...args),
+  };
+}
+
+// For troubleshooting, set the log level to DiagLogLevel.DEBUG.
+// OTel SDK diagnostics must not write to console because console output can be
+// surfaced in user-visible UI. Keep diagnostics in the debug log instead.
+diag.setLogger(createTelemetryDiagLogger(), DiagLogLevel.WARN);
 
 /**
  * Standard OTLP HTTP signal-specific paths per the OpenTelemetry specification.