diff --git a/.changeset/cli-spec-version-advisory.md b/.changeset/cli-spec-version-advisory.md
new file mode 100644
index 0000000000..46d24abfa3
--- /dev/null
+++ b/.changeset/cli-spec-version-advisory.md
@@ -0,0 +1,19 @@
+---
+'@objectstack/cli': minor
+---
+
+feat(cli): surface the migration guide when an app's specVersion trails the installed platform
+
+`os validate`, `os build`/`os compile`, and `os doctor` now emit a non-blocking
+advisory when the app's authored `manifest.specVersion` declares an OLDER major
+than the `@objectstack/spec` actually installed in its `node_modules` — pointing
+at the curated per-major migration guide (`https://docs.objectstack.ai/docs/releases/v<major>`,
+guaranteed to exist by `scripts/check-release-notes.mjs`).
+
+This closes a discoverability gap for downstream/third-party apps: on a platform
+upgrade the release notes were only reachable by reverse-engineering per-package
+`CHANGELOG.md` files. The advisory now surfaces the guide at the exact moment the
+upgrade is exercised. It never fails a build/validate and is not gated by
+`--strict`; it also appears in the `--json` output as `specVersionGap`. Logic
+lives in a new shared `checkSpecVersionGap()` util (unit-tested; installed
+version injectable for tests).
diff --git a/packages/cli/src/commands/compile.ts b/packages/cli/src/commands/compile.ts
index 24336c66c8..2888043c84 100644
--- a/packages/cli/src/commands/compile.ts
+++ b/packages/cli/src/commands/compile.ts
@@ -31,6 +31,7 @@ import {
   collectMetadataStats,
   printMetadataStats,
 } from '../utils/format.js';
+import { checkSpecVersionGap } from '../utils/spec-version.js';
 
 export default class Compile extends Command {
   static override description = 'Compile ObjectStack configuration to JSON artifact';
@@ -523,6 +524,10 @@ export default class Compile extends Command {
       const sizeKB = (jsonContent.length / 1024).toFixed(1);
       const stats = collectMetadataStats(config);
 
+      // Spec-version drift advisory (non-blocking): installed platform newer
+      // than the app declares → point at the migration guide.
+      const specGap = checkSpecVersionGap((config as { manifest?: { specVersion?: unknown } }).manifest);
+
       if (flags.json) {
         console.log(JSON.stringify({
           success: true,
@@ -532,6 +537,7 @@ export default class Compile extends Command {
           runtimeModule: runtimeBundle?.outputFileName ?? null,
           runtimeModuleSize: runtimeBundle?.size ?? 0,
           warnings: widgetWarnings,
+          specVersionGap: specGap,
           stats,
           duration: timer.elapsed(),
         }));
@@ -555,6 +561,11 @@ export default class Compile extends Command {
           `${path.join(path.dirname(output), runtimeBundle.outputFileName)} ${chalk.dim(`(${runtimeKB} KB, ${lowering.count} handler${lowering.count === 1 ? '' : 's'})`)}`,
         );
       }
+      if (specGap) {
+        console.log('');
+        console.log(chalk.yellow(`  ⚠ ${specGap.message}`));
+        console.log(chalk.dim(`      → ${specGap.hint}`));
+      }
       console.log('');
 
     } catch (error: any) {
diff --git a/packages/cli/src/commands/doctor.ts b/packages/cli/src/commands/doctor.ts
index 9daf391662..68f8b3a56f 100644
--- a/packages/cli/src/commands/doctor.ts
+++ b/packages/cli/src/commands/doctor.ts
@@ -8,6 +8,7 @@ import path from 'path';
 import { normalizeStackInput } from '@objectstack/spec';
 import { printHeader, printSuccess, printWarning, printError, printStep, printInfo } from '../utils/format.js';
 import { loadConfig, configExists } from '../utils/config.js';
+import { checkSpecVersionGap } from '../utils/spec-version.js';
 import { validateWidgetBindings } from '@objectstack/lint';
 
 interface HealthCheckResult {
@@ -487,6 +488,17 @@ export default class Doctor extends Command {
         const { config: rawConfig } = await loadConfig();
         const config: any = normalizeStackInput(rawConfig as Record<string, unknown>);
 
+        // Spec-version drift: installed platform newer than the app declares.
+        printStep('Checking platform spec version...');
+        const specGap = checkSpecVersionGap(config.manifest);
+        if (specGap) {
+          hasWarnings = true;
+          printWarning(`Platform spec         ${specGap.message}`);
+          console.log(chalk.dim(`      → ${specGap.hint}`));
+        } else {
+          printSuccess('Platform spec         Declared specVersion is current with the installed platform');
+        }
+
         // Circular dependency detection
         if (Array.isArray(config.objects) && config.objects.length > 0) {
           printStep('Checking for circular dependencies...');
diff --git a/packages/cli/src/commands/validate.ts b/packages/cli/src/commands/validate.ts
index d00db4495d..d7ebf63686 100644
--- a/packages/cli/src/commands/validate.ts
+++ b/packages/cli/src/commands/validate.ts
@@ -27,6 +27,7 @@ import {
   collectMetadataStats,
   printMetadataStats,
 } from '../utils/format.js';
+import { checkSpecVersionGap } from '../utils/spec-version.js';
 
 export default class Validate extends Command {
   static override description =
@@ -378,6 +379,10 @@ export default class Validate extends Command {
       // 4. Collect and display stats
       const stats = collectMetadataStats(config);
 
+      // Spec-version drift advisory (non-blocking): if the installed platform
+      // is a newer major than the app declares, point at the migration guide.
+      const specGap = checkSpecVersionGap(config.manifest);
+
       if (flags.json) {
         console.log(JSON.stringify({
           valid: true,
@@ -385,6 +390,7 @@ export default class Validate extends Command {
           stats,
           warnings: [...exprWarnings, ...widgetWarnings, ...styleWarnings, ...jsxWarnings, ...capWarnings, ...securityAdvisories],
           conversions: conversionNotices,
+          specVersionGap: specGap,
           duration: timer.elapsed(),
         }, null, 2));
         return;
@@ -460,6 +466,13 @@ export default class Validate extends Command {
         }
       }
 
+      // Non-blocking upgrade advisory — never gated by --strict.
+      if (specGap) {
+        console.log('');
+        console.log(chalk.yellow(`  ⚠ ${specGap.message}`));
+        console.log(chalk.dim(`      → ${specGap.hint}`));
+      }
+
       console.log('');
     } catch (error: any) {
       if (flags.json) {
diff --git a/packages/cli/src/utils/spec-version.test.ts b/packages/cli/src/utils/spec-version.test.ts
new file mode 100644
index 0000000000..4045d9b76f
--- /dev/null
+++ b/packages/cli/src/utils/spec-version.test.ts
@@ -0,0 +1,52 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { describe, it, expect } from 'vitest';
+import { checkSpecVersionGap } from './spec-version.js';
+
+describe('checkSpecVersionGap', () => {
+  it('flags an app declaring an older major than the installed platform', () => {
+    const gap = checkSpecVersionGap({ specVersion: '^12.0.0' }, '14.7.0');
+    expect(gap).not.toBeNull();
+    expect(gap!.declaredMajor).toBe(12);
+    expect(gap!.installedMajor).toBe(14);
+    expect(gap!.installedVersion).toBe('14.7.0');
+    expect(gap!.url).toBe('https://docs.objectstack.ai/docs/releases/v14');
+    expect(gap!.hint).toContain('https://docs.objectstack.ai/docs/releases/v14');
+  });
+
+  it('points at the guide for the INSTALLED major, not the declared one', () => {
+    // Two-major jump (12 → 14): the guide must be v14, the version on disk.
+    const gap = checkSpecVersionGap({ specVersion: '^12.0.0' }, '14.0.0');
+    expect(gap!.url).toBe('https://docs.objectstack.ai/docs/releases/v14');
+  });
+
+  it('is silent when declared major matches the installed platform', () => {
+    expect(checkSpecVersionGap({ specVersion: '^14.0.0' }, '14.7.0')).toBeNull();
+  });
+
+  it('is silent when the app declares a NEWER major (stale install, out of scope)', () => {
+    expect(checkSpecVersionGap({ specVersion: '^15.0.0' }, '14.7.0')).toBeNull();
+  });
+
+  it('is silent when no specVersion is declared', () => {
+    expect(checkSpecVersionGap({}, '14.7.0')).toBeNull();
+    expect(checkSpecVersionGap(undefined, '14.7.0')).toBeNull();
+    expect(checkSpecVersionGap(null, '14.7.0')).toBeNull();
+  });
+
+  it('is silent when the installed version cannot be resolved', () => {
+    expect(checkSpecVersionGap({ specVersion: '^12.0.0' }, null)).toBeNull();
+  });
+
+  it('parses the major out of assorted range spellings', () => {
+    for (const range of ['^12.0.0', '>=12', '12.x', '~12.3.0', '12 || 13']) {
+      const gap = checkSpecVersionGap({ specVersion: range }, '14.0.0');
+      expect(gap, range).not.toBeNull();
+      expect(gap!.declaredMajor, range).toBe(12);
+    }
+  });
+
+  it('ignores a non-string specVersion', () => {
+    expect(checkSpecVersionGap({ specVersion: 12 as unknown as string }, '14.0.0')).toBeNull();
+  });
+});
diff --git a/packages/cli/src/utils/spec-version.ts b/packages/cli/src/utils/spec-version.ts
new file mode 100644
index 0000000000..9ea8a6aa80
--- /dev/null
+++ b/packages/cli/src/utils/spec-version.ts
@@ -0,0 +1,101 @@
+// Copyright (c) 2025 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { createRequire } from 'module';
+
+/**
+ * Spec-version drift advisory.
+ *
+ * Surfaces the one thing an AI agent (or human) upgrading a third-party app
+ * almost never finds on its own: the curated per-major migration guide. When
+ * an app's authored `manifest.specVersion` declares an OLDER major than the
+ * `@objectstack/spec` actually installed in its `node_modules`, the platform
+ * moved ahead of the app and there is breaking-change guidance the author
+ * should read before proceeding. Every major from v12 on is guaranteed a
+ * `content/docs/releases/v<major>.mdx` page (enforced by
+ * `scripts/check-release-notes.mjs`), so the URL below never 404s.
+ *
+ * The check is advisory-only — it never fails a build/validate. It exists so
+ * the release notes are discoverable at the exact moment of the upgrade,
+ * instead of being reverse-engineered from per-package `CHANGELOG.md` files.
+ */
+
+const RELEASES_BASE = 'https://docs.objectstack.ai/docs/releases';
+
+export interface SpecVersionGap {
+  /** Major of the `@objectstack/spec` resolved from the app's node_modules. */
+  installedMajor: number;
+  /** Major declared by the app's `manifest.specVersion` range. */
+  declaredMajor: number;
+  /** Full installed spec version (e.g. `14.7.0`). */
+  installedVersion: string;
+  /** Canonical migration guide for the installed major. */
+  url: string;
+  /** Ready-to-print one-line advisory. */
+  message: string;
+  /** Ready-to-print follow-up pointing at the guide. */
+  hint: string;
+}
+
+/** Parse the leading major integer out of a semver range like `^12.0.0`, `>=13`, `14.x`. */
+function parseMajor(range: unknown): number | null {
+  if (typeof range !== 'string') return null;
+  const m = range.match(/\d+/);
+  if (!m) return null;
+  const major = Number.parseInt(m[0], 10);
+  return Number.isFinite(major) ? major : null;
+}
+
+/** Resolve the installed `@objectstack/spec` version from the app being operated on. */
+function resolveInstalledSpecVersion(): string | null {
+  try {
+    // Resolve relative to the CWD (the app), not the CLI install, so a globally
+    // linked CLI still reports the app's locked spec version. Fall back to the
+    // CLI's own resolution if the app doesn't hoist spec to its root.
+    const requireFromApp = createRequire(`${process.cwd()}/package.json`);
+    const pkg = requireFromApp('@objectstack/spec/package.json') as { version?: string };
+    if (typeof pkg.version === 'string') return pkg.version;
+  } catch {
+    // ignore — try the CLI-relative resolution below
+  }
+  try {
+    const requireFromCli = createRequire(import.meta.url);
+    const pkg = requireFromCli('@objectstack/spec/package.json') as { version?: string };
+    if (typeof pkg.version === 'string') return pkg.version;
+  } catch {
+    // ignore — spec not resolvable, no advisory
+  }
+  return null;
+}
+
+/**
+ * Compute a spec-version drift advisory for the given app manifest, or `null`
+ * when there is nothing to say (spec unresolvable, no `specVersion` declared,
+ * or the declared major already matches / leads the installed platform).
+ */
+export function checkSpecVersionGap(
+  manifest: { specVersion?: unknown } | undefined | null,
+  /** Injectable for tests; defaults to the spec resolved from the app on disk. */
+  installedVersion: string | null = resolveInstalledSpecVersion(),
+): SpecVersionGap | null {
+  const declaredMajor = parseMajor(manifest?.specVersion);
+  if (declaredMajor == null) return null;
+
+  if (!installedVersion) return null;
+  const installedMajor = parseMajor(installedVersion);
+  if (installedMajor == null) return null;
+
+  // Only the upgrade case: the platform on disk is newer than what the app
+  // declares. (declaredMajor > installedMajor is a stale/mismatched install —
+  // a different problem, out of scope for release-note discoverability.)
+  if (declaredMajor >= installedMajor) return null;
+
+  const url = `${RELEASES_BASE}/v${installedMajor}`;
+  return {
+    installedMajor,
+    declaredMajor,
+    installedVersion,
+    url,
+    message: `Installed @objectstack/spec is v${installedVersion} but this app declares specVersion for v${declaredMajor}.`,
+    hint: `Review the v${installedMajor} migration guide before bumping specVersion: ${url}`,
+  };
+}