diff --git a/src/cli/index.ts b/src/cli/index.ts
index c51e490a8d..1143866882 100644
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -154,8 +154,9 @@ program.hook('preAction', async (thisCommand, actionCommand) => {
     process.env.NO_COLOR = '1';
   }
 
-  // Show first-run telemetry notice (if not seen). Suppress it whenever the run
-  // asked for JSON so stdout stays a single valid JSON document (see isJsonRun).
+  // Show first-run telemetry notice (if not seen). It's written to stderr, so it
+  // never pollutes stdout — but --json runs still defer it (see isJsonRun) so the
+  // very first invocation stays free of any incidental output on either stream.
   await maybeShowTelemetryNotice({ silent: isJsonRun(actionCommand) });
 
   // Track command execution (use actionCommand to get the actual subcommand)
diff --git a/src/telemetry/index.ts b/src/telemetry/index.ts
index 3eb1978e3f..0e4d6290eb 100644
--- a/src/telemetry/index.ts
+++ b/src/telemetry/index.ts
@@ -197,8 +197,9 @@ export async function maybeShowTelemetryNotice(
       return;
     }
 
-    // Display notice
-    console.log(
+    // Display notice on stderr, not stdout: stdout is reserved for command
+    // output (raw passthrough text, JSON, etc.) and must stay parser/pipe-safe.
+    console.error(
       'Note: OpenSpec collects anonymous usage stats. Opt out: OPENSPEC_TELEMETRY=0 or openspec config set telemetry.enabled false'
     );
 
diff --git a/test/telemetry/index.test.ts b/test/telemetry/index.test.ts
index 3d2afe9151..7db56ddeed 100644
--- a/test/telemetry/index.test.ts
+++ b/test/telemetry/index.test.ts
@@ -9,7 +9,7 @@ import { getTelemetryConfig } from '../../src/telemetry/config.js';
 describe('telemetry/index', () => {
   let tempDir: string;
   let originalEnv: NodeJS.ProcessEnv;
-  let consoleLogSpy: ReturnType<typeof vi.spyOn>;
+  let consoleErrorSpy: ReturnType<typeof vi.spyOn>;
   let fetchSpy: ReturnType<typeof vi.spyOn<typeof globalThis, 'fetch'>>;
 
   beforeEach(() => {
@@ -28,8 +28,8 @@ describe('telemetry/index', () => {
     // Clear all mocks
     vi.clearAllMocks();
 
-    // Spy on console.log for notice tests
-    consoleLogSpy = vi.spyOn(console, 'log').mockImplementation(() => {});
+    // Notice is written to stderr so it never pollutes stdout (raw/JSON output)
+    consoleErrorSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
     // Telemetry must never reach the real network in tests
     fetchSpy = vi
       .spyOn(globalThis, 'fetch')
@@ -167,7 +167,7 @@ describe('telemetry/index', () => {
 
       await maybeShowTelemetryNotice();
 
-      expect(consoleLogSpy).not.toHaveBeenCalled();
+      expect(consoleErrorSpy).not.toHaveBeenCalled();
     });
 
     it('should not show notice when telemetry.enabled is false', async () => {
@@ -176,21 +176,21 @@ describe('telemetry/index', () => {
 
       await maybeShowTelemetryNotice();
 
-      expect(consoleLogSpy).not.toHaveBeenCalled();
+      expect(consoleErrorSpy).not.toHaveBeenCalled();
     });
 
     it('should show notice on the first non-silent run, then never repeat it', async () => {
       enableTelemetry();
 
       await maybeShowTelemetryNotice();
-      expect(consoleLogSpy).toHaveBeenCalledTimes(1);
-      expect(consoleLogSpy).toHaveBeenCalledWith(
+      expect(consoleErrorSpy).toHaveBeenCalledTimes(1);
+      expect(consoleErrorSpy).toHaveBeenCalledWith(
         expect.stringContaining('OpenSpec collects anonymous usage stats')
       );
 
       // noticeSeen is now persisted: a second run stays quiet.
       await maybeShowTelemetryNotice();
-      expect(consoleLogSpy).toHaveBeenCalledTimes(1);
+      expect(consoleErrorSpy).toHaveBeenCalledTimes(1);
     });
 
     it('should suppress the notice in silent (--json) mode and defer the disclosure', async () => {
@@ -198,15 +198,15 @@ describe('telemetry/index', () => {
 
       // A first-ever run in --json mode must not pollute stdout.
       await maybeShowTelemetryNotice({ silent: true });
-      expect(consoleLogSpy).not.toHaveBeenCalled();
+      expect(consoleErrorSpy).not.toHaveBeenCalled();
 
       // The disclosure must be deferred, not consumed: noticeSeen stays unset.
       expect((await getTelemetryConfig()).noticeSeen).toBeFalsy();
 
       // Disclosure is only deferred, not skipped: the next non-JSON run shows it.
       await maybeShowTelemetryNotice();
-      expect(consoleLogSpy).toHaveBeenCalledTimes(1);
-      expect(consoleLogSpy).toHaveBeenCalledWith(
+      expect(consoleErrorSpy).toHaveBeenCalledTimes(1);
+      expect(consoleErrorSpy).toHaveBeenCalledWith(
         expect.stringContaining('OpenSpec collects anonymous usage stats')
       );
     });