diff --git a/.changeset/suppress-telemetry-notice-json.md b/.changeset/suppress-telemetry-notice-json.md
new file mode 100644
index 0000000000..02760341b1
--- /dev/null
+++ b/.changeset/suppress-telemetry-notice-json.md
@@ -0,0 +1,8 @@
+---
+"@fission-ai/openspec": patch
+---
+
+Suppress the first-run telemetry disclosure notice when `--json` is used. On a
+first-ever run the notice was written to stdout and could break `--json`
+consumers; it is now deferred to the first later non-JSON run, keeping `--json`
+output valid while still guaranteeing the disclosure.
diff --git a/openspec/changes/suppress-telemetry-notice-in-json/.openspec.yaml b/openspec/changes/suppress-telemetry-notice-in-json/.openspec.yaml
new file mode 100644
index 0000000000..878dc3156e
--- /dev/null
+++ b/openspec/changes/suppress-telemetry-notice-in-json/.openspec.yaml
@@ -0,0 +1,2 @@
+schema: spec-driven
+created: 2026-08-07
diff --git a/openspec/changes/suppress-telemetry-notice-in-json/proposal.md b/openspec/changes/suppress-telemetry-notice-in-json/proposal.md
new file mode 100644
index 0000000000..579026b05c
--- /dev/null
+++ b/openspec/changes/suppress-telemetry-notice-in-json/proposal.md
@@ -0,0 +1,44 @@
+# Suppress the first-run telemetry notice in --json mode
+
+## Why
+
+`openspec <cmd> --json` is meant to emit exactly one machine-readable JSON
+document on stdout so agents and automation can parse it. Spinner suppression
+and structured JSON errors already ship on main, but one stdout writer remains:
+the first-run telemetry disclosure notice.
+
+On a user's first-ever command, `maybeShowTelemetryNotice()` runs from the
+global `preAction` hook and `console.log`s the disclosure to **stdout** — before
+the command's JSON payload. A `--json` consumer parsing that first run gets
+invalid JSON. It is first-run-only (the notice sets `noticeSeen`), but that is
+exactly the run an automation is most likely to hit on a fresh machine or CI
+image.
+
+## What Changes
+
+- `maybeShowTelemetryNotice()` accepts a `silent` option. When silent, it prints
+  nothing **and** leaves `noticeSeen` unset, so the disclosure is deferred rather
+  than skipped.
+- The `preAction` hook passes `silent: true` when the executing command asked
+  for JSON, decided by `isJsonRun(command)`. `--json` reaches commands three
+  ways, so a single parsed option (`opts().json`) is not enough: on the leaf
+  (`status --json`), on a parent group read via `optsWithGlobals`
+  (`workset --json list`), and as a residual arg on permissive groups that never
+  declare the option (`openspec store --json`). `isJsonRun` checks
+  `optsWithGlobals().json` and `command.args`, covering all three.
+
+Net effect: any `--json` invocation never emits the notice on stdout; the user
+still sees the disclosure on their first later non-JSON run. Suppressing is
+always safe — worst case the disclosure defers one run. Telemetry remains opt-out
+and otherwise unchanged.
+
+Out of scope: a few commands write scriptable output to stdout without a `--json`
+flag (`completion generate`, `config get`, `config path`, the hidden `__complete`).
+Their first-run notice pollution is a separate, pre-existing issue not addressed
+here.
+
+## Impact
+
+- Affected specs: `telemetry` (MODIFIED: First-run telemetry notice)
+- Affected code: `src/telemetry/index.ts`, `src/cli/index.ts`
+- No change to non-JSON behavior; no new events or data collected.
diff --git a/openspec/changes/suppress-telemetry-notice-in-json/specs/telemetry/spec.md b/openspec/changes/suppress-telemetry-notice-in-json/specs/telemetry/spec.md
new file mode 100644
index 0000000000..8e1316eee2
--- /dev/null
+++ b/openspec/changes/suppress-telemetry-notice-in-json/specs/telemetry/spec.md
@@ -0,0 +1,28 @@
+## MODIFIED Requirements
+
+### Requirement: First-run telemetry notice
+The system SHALL display a one-line telemetry disclosure notice on the first command execution, before any telemetry is sent. In `--json` mode the system SHALL NOT display the notice on that run and SHALL leave `noticeSeen` unset, deferring the disclosure to the first later non-JSON run.
+
+#### Scenario: First command execution
+- **WHEN** a user runs their first openspec command without `--json`
+- **AND** telemetry is enabled
+- **THEN** the system displays: "Note: OpenSpec collects anonymous usage stats. Opt out: OPENSPEC_TELEMETRY=0"
+
+#### Scenario: Subsequent command execution
+- **WHEN** a user has already seen the notice (noticeSeen: true in config)
+- **THEN** the system does not display the notice
+
+#### Scenario: Notice before telemetry
+- **WHEN** displaying the first-run notice
+- **THEN** the notice appears before any telemetry event is sent
+
+#### Scenario: First command execution in JSON mode
+- **WHEN** a user's first openspec command passes `--json`
+- **AND** telemetry is enabled
+- **THEN** the system displays no notice on stdout
+- **AND** `noticeSeen` remains unset
+
+#### Scenario: Disclosure deferred, not skipped
+- **WHEN** a user's first run was in `--json` mode and displayed no notice
+- **AND** the user later runs a command without `--json`
+- **THEN** the system displays the disclosure notice on that later run
diff --git a/openspec/changes/suppress-telemetry-notice-in-json/tasks.md b/openspec/changes/suppress-telemetry-notice-in-json/tasks.md
new file mode 100644
index 0000000000..b1af654c0d
--- /dev/null
+++ b/openspec/changes/suppress-telemetry-notice-in-json/tasks.md
@@ -0,0 +1,9 @@
+# Tasks
+
+## 1. Suppress notice in JSON mode
+- [x] 1.1 Add a `silent` option to `maybeShowTelemetryNotice()` that skips the notice and leaves `noticeSeen` unset
+- [x] 1.2 Read `actionCommand.opts().json` in the `preAction` hook and pass `silent` accordingly
+
+## 2. Tests
+- [x] 2.1 Assert a first-run `--json` (silent) call prints nothing and does not mark the notice seen
+- [x] 2.2 Assert the disclosure still appears on the first later non-silent run
diff --git a/src/cli/index.ts b/src/cli/index.ts
index 6772643c68..f932f53dba 100644
--- a/src/cli/index.ts
+++ b/src/cli/index.ts
@@ -115,6 +115,27 @@ export function getCommandPath(command: Command): string {
   return names.join(':') || 'openspec';
 }
 
+/**
+ * True when the executing command asked for JSON output — used to suppress the
+ * first-run telemetry notice so stdout stays a single valid JSON document.
+ *
+ * `--json` reaches commands three ways, so a single parsed option is not enough:
+ * - declared on the leaf (`openspec status --json`) → `opts().json`
+ * - declared on a parent group and read via globals (`openspec workset --json list`)
+ *   → `optsWithGlobals().json`
+ * - a residual arg on a permissive group that never declares the option
+ *   (`openspec store --json`, which detects it from `command.args`) → `args`
+ *
+ * Suppressing is always safe: the disclosure is only deferred to the next
+ * non-JSON run, never lost, whereas printing it on a JSON run corrupts stdout.
+ */
+export function isJsonRun(command: Command): boolean {
+  return (
+    command.optsWithGlobals().json === true ||
+    command.args.includes('--json')
+  );
+}
+
 program
   .name('openspec')
   .description('AI-native system for spec-driven development')
@@ -133,8 +154,9 @@ program.hook('preAction', async (thisCommand, actionCommand) => {
     process.env.NO_COLOR = '1';
   }
 
-  // Show first-run telemetry notice (if not seen)
-  await maybeShowTelemetryNotice();
+  // 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).
+  await maybeShowTelemetryNotice({ silent: isJsonRun(actionCommand) });
 
   // Track command execution (use actionCommand to get the actual subcommand)
   const commandPath = getCommandPath(actionCommand);
diff --git a/src/telemetry/index.ts b/src/telemetry/index.ts
index fce6a67534..3eb1978e3f 100644
--- a/src/telemetry/index.ts
+++ b/src/telemetry/index.ts
@@ -177,7 +177,9 @@ export async function trackCommand(commandName: string, version: string): Promis
 /**
  * Show first-run telemetry notice if not already seen.
  */
-export async function maybeShowTelemetryNotice(): Promise<void> {
+export async function maybeShowTelemetryNotice(
+  options: { silent?: boolean } = {}
+): Promise<void> {
   if (!isTelemetryEnabled()) {
     return;
   }
@@ -188,6 +190,13 @@ export async function maybeShowTelemetryNotice(): Promise<void> {
       return;
     }
 
+    // In --json mode the notice would pollute stdout and break parsers, so
+    // defer it: skip the notice AND leave noticeSeen unset so the disclosure
+    // still appears on the user's first later non-JSON run.
+    if (options.silent) {
+      return;
+    }
+
     // Display notice
     console.log(
       'Note: OpenSpec collects anonymous usage stats. Opt out: OPENSPEC_TELEMETRY=0 or openspec config set telemetry.enabled false'
diff --git a/test/core/cli-is-json-run.test.ts b/test/core/cli-is-json-run.test.ts
new file mode 100644
index 0000000000..fa4110a0be
--- /dev/null
+++ b/test/core/cli-is-json-run.test.ts
@@ -0,0 +1,79 @@
+import { describe, it, expect } from 'vitest';
+import { Command, Option } from 'commander';
+
+import { isJsonRun } from '../../src/cli/index.js';
+
+/**
+ * Reproduce the three ways `--json` reaches a command in the real CLI, so a
+ * future refactor of the telemetry-notice guard can't silently reintroduce
+ * first-run stdout pollution for `store --json` / `workset --json <sub>`.
+ */
+function buildProgram(capture: (command: Command) => void): Command {
+  const program = new Command();
+  program.name('openspec').exitOverride();
+  program.configureOutput({ writeOut: () => {}, writeErr: () => {} });
+  program.option('--no-color', 'Disable color output');
+  program.hook('preAction', (_thisCommand, actionCommand) => {
+    capture(actionCommand);
+  });
+
+  // 1. Leaf declares --json (e.g. `openspec status --json`).
+  program
+    .command('status')
+    .option('--json', 'Output as JSON')
+    .action(() => {});
+
+  // 2. Permissive bare group that never declares --json and detects it from
+  //    residual args (e.g. `openspec store --json`).
+  const store = program.command('store');
+  store.allowExcessArguments(true);
+  store.allowUnknownOption(true);
+  store.action(() => {});
+
+  // 3. Parent group declares --json (read via optsWithGlobals) with its own
+  //    subcommands (e.g. `openspec workset --json list`).
+  const workset = program.command('workset');
+  workset.addOption(new Option('--json', 'Output as JSON').hideHelp());
+  workset
+    .command('list')
+    .option('--json', 'Output as JSON')
+    .action(() => {});
+
+  return program;
+}
+
+describe('isJsonRun', () => {
+  async function actionCommandFor(argv: string[]): Promise<Command> {
+    let captured: Command | undefined;
+    const program = buildProgram((command) => {
+      captured = command;
+    });
+    await program.parseAsync(['node', 'openspec', ...argv]);
+    if (!captured) throw new Error(`no action command captured for: ${argv.join(' ')}`);
+    return captured;
+  }
+
+  it('detects --json declared on the leaf command', async () => {
+    expect(isJsonRun(await actionCommandFor(['status', '--json']))).toBe(true);
+  });
+
+  it('detects --json as a residual arg on a permissive bare group', async () => {
+    expect(isJsonRun(await actionCommandFor(['store', '--json']))).toBe(true);
+  });
+
+  it('detects --json on a parent group placed before the subcommand', async () => {
+    expect(isJsonRun(await actionCommandFor(['workset', '--json', 'list']))).toBe(true);
+  });
+
+  it('detects --json declared on the subcommand leaf', async () => {
+    expect(isJsonRun(await actionCommandFor(['workset', 'list', '--json']))).toBe(true);
+  });
+
+  it('is false when no --json is present', async () => {
+    expect(isJsonRun(await actionCommandFor(['status']))).toBe(false);
+  });
+
+  it('is false for a bare group with unrelated residual args', async () => {
+    expect(isJsonRun(await actionCommandFor(['store', 'bogus']))).toBe(false);
+  });
+});
diff --git a/test/telemetry/index.test.ts b/test/telemetry/index.test.ts
index b3b21f7aa9..3d2afe9151 100644
--- a/test/telemetry/index.test.ts
+++ b/test/telemetry/index.test.ts
@@ -4,6 +4,7 @@ import * as path from 'node:path';
 import * as os from 'node:os';
 
 import { isTelemetryEnabled, maybeShowTelemetryNotice, shutdown, trackCommand } from '../../src/telemetry/index.js';
+import { getTelemetryConfig } from '../../src/telemetry/config.js';
 
 describe('telemetry/index', () => {
   let tempDir: string;
@@ -177,6 +178,38 @@ describe('telemetry/index', () => {
 
       expect(consoleLogSpy).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.stringContaining('OpenSpec collects anonymous usage stats')
+      );
+
+      // noticeSeen is now persisted: a second run stays quiet.
+      await maybeShowTelemetryNotice();
+      expect(consoleLogSpy).toHaveBeenCalledTimes(1);
+    });
+
+    it('should suppress the notice in silent (--json) mode and defer the disclosure', async () => {
+      enableTelemetry();
+
+      // A first-ever run in --json mode must not pollute stdout.
+      await maybeShowTelemetryNotice({ silent: true });
+      expect(consoleLogSpy).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.stringContaining('OpenSpec collects anonymous usage stats')
+      );
+    });
   });
 
   describe('trackCommand', () => {