diff --git a/package.json b/package.json
index 2d54ffa..6833517 100644
--- a/package.json
+++ b/package.json
@@ -63,7 +63,7 @@
   "scripts": {
     "build": "node -e \"require('node:fs').rmSync('dist', { recursive: true, force: true })\" && tsc -p tsconfig.json && tsc -p tsconfig.cjs.json && node scripts/finalize-build.mjs",
     "typecheck": "tsc -p tsconfig.json --noEmit && tsc -p tsconfig.cjs.json --noEmit",
-    "test": "node --test tests/feedback-*.test.mjs",
+    "test": "node --test tests/feedback-*.test.mjs tests/update.test.mjs",
     "ci:generate": "hollywood generate 'ci/**/*.ts' --source-root ci --output .",
     "test:package": "node scripts/verify-staging-package.mjs"
   },
diff --git a/scripts/verify-staging-package.mjs b/scripts/verify-staging-package.mjs
index 697b6bd..ef22409 100644
--- a/scripts/verify-staging-package.mjs
+++ b/scripts/verify-staging-package.mjs
@@ -43,11 +43,11 @@ try {
     [
       '--test',
       ...readdirSync('tests')
-        .filter((name) => /^feedback-.*\.test\.mjs$/.test(name))
+        .filter((name) => /^feedback-.*\.test\.mjs$/.test(name) || name === 'update.test.mjs')
         .map((name) => join('tests', name)),
     ],
     {
-      env: { ...process.env, FEEDBACK_PACKAGE_ROOT: installed },
+      env: { ...process.env, FEEDBACK_PACKAGE_ROOT: installed, UPDATE_PACKAGE_ROOT: installed },
       stdio: 'inherit',
     },
   );
diff --git a/src/custom/README.md b/src/custom/README.md
index de39bee..09d1446 100644
--- a/src/custom/README.md
+++ b/src/custom/README.md
@@ -22,3 +22,20 @@ node --test tests/machine-aliases.test.mjs
 node --test tests/ssh-paths.test.mjs
 python3 tests/ssh-picker-pty.py
 ```
+
+# Update command
+
+`dedalus update --check` reports the current and latest stable GitHub release
+without probing or modifying the installation. `dedalus update` upgrades a
+verified global npm installation to that exact version, or upgrades a verified
+Homebrew formula after checking that Homebrew publishes the same version.
+A GitHub release that has not reached the package manager does not authorize
+an upgrade. Equal or older releases never trigger an installation.
+
+Standalone downloads, Homebrew casks, local npm installs, Windows installs and
+unrecognized layouts receive manual update instructions. No removed installer
+scripts are invoked, and the Node executable is never replaced. Startup update
+prompts are not included. Development and prerelease versions require an
+explicit update through the original package manager.
+
+Run `npm run build && node --test tests/update.test.mjs` to check this contract.
diff --git a/src/custom/machines.ts b/src/custom/machines.ts
index 8341b8d..481beb2 100644
--- a/src/custom/machines.ts
+++ b/src/custom/machines.ts
@@ -1,6 +1,7 @@
 /** SSH selection that shares the CLI's authentication and error settings. */
 
 import { Command, Option } from 'commander'
+import { registerUpdateCommand } from './update.js'
 import SDK from '../sdk/index.js'
 import type { CliAuthDefinition } from '../cli/login.js'
 import {
@@ -62,7 +63,7 @@ export const addMachineAliases = (
       }, options.auth)
     })
   program.addCommand(ssh)
-  return program
+  return registerUpdateCommand(program)
 }
 
 const aliasCommand = (program: Command, name: string): Command => {
diff --git a/src/custom/update.ts b/src/custom/update.ts
new file mode 100644
index 0000000..c56621d
--- /dev/null
+++ b/src/custom/update.ts
@@ -0,0 +1,119 @@
+/** Updates only installations whose package manager ownership can be proved. */
+import { execFileSync, spawnSync } from 'node:child_process'
+import { realpathSync } from 'node:fs'
+import { join, relative, isAbsolute } from 'node:path'
+import { Command } from 'commander'
+
+const latestURL = 'https://api.github.com/repos/dedalus-labs/dedalus-cli/releases/latest'
+
+type Effects = {
+  current: string
+  entry: string
+  executable: string
+  platform: string
+  latest: () => Promise<string>
+  realpath: (path: string) => string
+  output: (name: string, args: string[]) => string
+  run: (name: string, args: string[]) => void
+  print: (message: string) => void
+}
+
+// Only stable release numbers authorize an installation change. Development and
+// prerelease builds need an explicit package-manager command from their owner.
+export const newerStable = (candidate: string, current: string): boolean => {
+  const parse = (value: string) => {
+    if (!/^v?(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)$/u.test(value)) return undefined
+    return value.replace(/^v/u, '').split('.').map(BigInt)
+  }
+  const next = parse(candidate)
+  const previous = parse(current)
+  if (!next || !previous) throw new Error('Cannot safely compare release versions; update with your original package manager.')
+  for (let i = 0; i < 3; i++) {
+    if (next[i]! !== previous[i]!) return next[i]! > previous[i]!
+  }
+  return false
+}
+
+const within = (path: string, directory: string): boolean => {
+  const child = relative(directory, path)
+  return child !== '' && child !== '..' && !child.startsWith('../') && !child.startsWith('..\\') && !isAbsolute(child)
+}
+
+export const updateCLI = async (check: boolean, effects: Effects): Promise<void> => {
+  const latest = await effects.latest()
+  effects.print(`Current version: ${effects.current}\nLatest version:  ${latest}`)
+  const newer = newerStable(latest, effects.current)
+  if (!newer) {
+    effects.print('The installed version is current or newer than the latest stable release.')
+    return
+  }
+  if (check) return
+  const version = latest.replace(/^v/u, '')
+  const query = (name: string, args: string[]): string | undefined => {
+    try { return effects.output(name, args).trim() || undefined } catch { return undefined }
+  }
+  const resolve = (path: string): string | undefined => {
+    try { return effects.realpath(path) } catch { return undefined }
+  }
+  const executable = resolve(effects.executable)
+  const entry = resolve(effects.entry)
+
+  // A Node launch updates the package, never process.execPath (the Node runtime).
+  if (entry && effects.platform !== 'win32') {
+    const root = query('npm', ['root', '--global'])
+    const installedEntry = root && resolve(join(root, 'dedalus-cli', 'dist', 'esm', 'bin.js'))
+    if (installedEntry === entry) {
+      const published = query('npm', ['view', `dedalus-cli@${version}`, 'version'])
+      if (published !== version) throw new Error(`Release ${version} is not available from npm yet; no changes made.`)
+      effects.print(`Running: npm install --global dedalus-cli@${version}`)
+      effects.run('npm', ['install', '--global', `dedalus-cli@${version}`])
+      return
+    }
+  }
+  if (executable && effects.platform !== 'win32') {
+    const formula = query('brew', ['--prefix', 'dedalus'])
+    const prefix = formula && resolve(formula)
+    if (prefix && within(executable, prefix)) {
+      effects.run('brew', ['update'])
+      const info = query('brew', ['info', '--json=v2', '--formula', 'dedalus'])
+      const available: unknown = info ? JSON.parse(info) : undefined
+      const formulaVersion = (available as { formulae?: { versions?: { stable?: string } }[] } | undefined)?.formulae?.[0]?.versions?.stable
+      if (formulaVersion !== version) throw new Error(`Homebrew has not published ${version}; no package upgrade performed.`)
+      effects.print('Running: brew upgrade --formula dedalus')
+      effects.run('brew', ['upgrade', '--formula', 'dedalus'])
+      return
+    }
+  }
+  effects.print('Automatic update is unavailable for this installation. Update with the package manager you originally used. For standalone binaries, download the matching release at https://github.com/dedalus-labs/dedalus-cli/releases/latest and replace the CLI after it exits.')
+}
+
+export const registerUpdateCommand = (program: Command): Command => {
+  program.command('update').description('Update the CLI using its owning package manager')
+    .option('--check', 'Check for a newer stable release without installing')
+    .action(async (flags: { check?: boolean }, command: Command) => {
+      try {
+        await updateCLI(Boolean(flags.check), {
+          current: program.version() ?? '', entry: process.argv[1] ?? '',
+          executable: process.execPath, platform: process.platform,
+          latest: async () => {
+            const response = await fetch(latestURL, { signal: AbortSignal.timeout(10_000), headers: { Accept: 'application/vnd.github+json' } })
+            if (!response.ok) throw new Error(`Release check failed: HTTP ${response.status}`)
+            const release: unknown = await response.json()
+            if (typeof release !== 'object' || release === null || !('tag_name' in release) || typeof release.tag_name !== 'string') throw new Error('Release response is missing tag_name')
+            return release.tag_name
+          },
+          realpath: realpathSync,
+          output: (name, args) => execFileSync(name, args, { encoding: 'utf8', timeout: 30_000, stdio: ['ignore', 'pipe', 'ignore'] }),
+          run: (name, args) => {
+            const result = spawnSync(name, args, { stdio: 'inherit' })
+            if (result.error) throw result.error
+            if (result.status !== 0) throw new Error(`${name} failed${result.signal ? ` (${result.signal})` : ` (exit ${result.status})`}`)
+          },
+          print: (message) => console.log(message),
+        })
+      } catch (error) {
+        command.error(error instanceof Error ? error.message : String(error), { exitCode: 1 })
+      }
+    })
+  return program
+}
diff --git a/tests/update.test.mjs b/tests/update.test.mjs
new file mode 100644
index 0000000..55be87f
--- /dev/null
+++ b/tests/update.test.mjs
@@ -0,0 +1,98 @@
+import { test } from 'node:test'
+import assert from 'node:assert/strict'
+import { resolve } from 'node:path'
+import { pathToFileURL } from 'node:url'
+
+const packageRoot = process.env.UPDATE_PACKAGE_ROOT ?? '.'
+const { newerStable, updateCLI } = await import(pathToFileURL(resolve(packageRoot, 'dist/esm/custom/update.js')).href)
+const { getProgram } = await import(pathToFileURL(resolve(packageRoot, 'dist/esm/index.js')).href)
+
+const fixture = (overrides = {}) => {
+  const runs = []
+  const queries = []
+  const effects = {
+    current: '0.7.0', entry: '/global/dedalus-cli/dist/esm/bin.js', executable: '/usr/bin/node', platform: 'linux',
+    latest: async () => 'v0.8.0', realpath: (path) => path,
+    output: (name, args) => {
+      queries.push([name, args])
+      if (name === 'npm' && args[0] === 'root') return '/global'
+      if (name === 'npm' && args[0] === 'view') return '0.8.0'
+      throw new Error('not installed')
+    },
+    run: (name, args) => runs.push([name, args]), print: () => {}, ...overrides,
+  }
+  return { effects, runs, queries }
+}
+
+test('invariant check mode never probes or mutates an installation', async () => {
+  const { effects, runs, queries } = fixture({ realpath: () => { throw new Error('must not resolve') } })
+  await updateCLI(true, effects)
+  assert.deepEqual(runs, [])
+  assert.deepEqual(queries, [])
+})
+
+test('invariant equal or older releases never install', async () => {
+  for (const current of ['0.8.0', '0.9.0', '1.0.0']) {
+    const { effects, runs, queries } = fixture({ current })
+    await updateCLI(false, effects)
+    assert.deepEqual(runs, [])
+    assert.deepEqual(queries, [])
+  }
+})
+
+test('invariant global npm updates pin the release and never replace Node', async () => {
+  const { effects, runs } = fixture()
+  await updateCLI(false, effects)
+  assert.deepEqual(runs, [['npm', ['install', '--global', 'dedalus-cli@0.8.0']]])
+})
+
+test('invariant missing npm publication leaves the installation unchanged', async () => {
+  const { effects, runs } = fixture({ output: (_name, args) => args[0] === 'root' ? '/global' : '0.6.0' })
+  await assert.rejects(updateCLI(false, effects), /not available from npm/)
+  assert.deepEqual(runs, [])
+})
+
+test('invariant local, unknown and Windows installations are never mutated', async () => {
+  for (const overrides of [{ entry: '/project/node_modules/dedalus-cli/dist/esm/bin.js' }, { entry: '/standalone/dedalus', executable: '/standalone/dedalus' }, { platform: 'win32' }]) {
+    const { effects, runs } = fixture(overrides)
+    await updateCLI(false, effects)
+    assert.deepEqual(runs, [])
+  }
+})
+
+test('invariant Homebrew ownership and publication must both match before upgrade', async () => {
+  for (const [executable, published, upgrade] of [['/brew/Cellar/dedalus/0.7.0/bin/dedalus', '0.8.0', true], ['/brew/Cellar/dedalus-other/bin/dedalus', '0.8.0', false], ['/brew/Cellar/dedalus/0.7.0/bin/dedalus', '0.6.0', false]]) {
+    const { effects, runs } = fixture({ entry: '/standalone/dedalus', executable,
+      output: (name, args) => {
+        if (name !== 'brew') throw new Error('unavailable')
+        return args[0] === '--prefix' ? '/brew/Cellar/dedalus/0.7.0' : JSON.stringify({ formulae: [{ versions: { stable: published } }] })
+      },
+    })
+    if (published === '0.6.0') await assert.rejects(updateCLI(false, effects), /has not published/)
+    else await updateCLI(false, effects)
+    assert.equal(runs.some(([, args]) => args[0] === 'upgrade'), upgrade)
+  }
+})
+
+test('invariant unrecognized versions cannot authorize installation', () => {
+  for (const value of ['dev', '0.8.0-rc.1', '0.8', '0.8.0; echo unsafe']) assert.throws(() => newerStable(value, '0.7.0'))
+  assert.equal(newerStable('0.10.0', '0.9.0'), true)
+})
+
+test('design update is registered with a read-only check option', () => {
+  const update = getProgram().commands.find((command) => command.name() === 'update')
+  assert.ok(update)
+  assert.ok(update.options.some((option) => option.long === '--check'))
+})
+
+test('invariant release lookup failure never touches an installation', async () => {
+  const { effects, queries, runs } = fixture({ latest: async () => { throw new Error('offline') } })
+  await assert.rejects(updateCLI(false, effects), /offline/)
+  assert.deepEqual(queries, [])
+  assert.deepEqual(runs, [])
+})
+
+test('invariant installer failure propagates to the caller', async () => {
+  const { effects } = fixture({ run: () => { throw new Error('permission denied') } })
+  await assert.rejects(updateCLI(false, effects), /permission denied/)
+})