diff --git a/src/hooks/auto-update-checker/cache.ts b/src/hooks/auto-update-checker/cache.ts
new file mode 100644
index 0000000..855843a
--- /dev/null
+++ b/src/hooks/auto-update-checker/cache.ts
@@ -0,0 +1,18 @@
+import * as fs from "node:fs"
+import { VERSION_FILE } from "./constants"
+import { log } from "../../shared/logger"
+
+export function invalidateCache(): boolean {
+  try {
+    if (fs.existsSync(VERSION_FILE)) {
+      fs.unlinkSync(VERSION_FILE)
+      log(`[auto-update-checker] Cache invalidated: ${VERSION_FILE}`)
+      return true
+    }
+    log("[auto-update-checker] Version file not found, nothing to invalidate")
+    return false
+  } catch (err) {
+    log("[auto-update-checker] Failed to invalidate cache:", err)
+    return false
+  }
+}
diff --git a/src/hooks/auto-update-checker/checker.ts b/src/hooks/auto-update-checker/checker.ts
new file mode 100644
index 0000000..95babfa
--- /dev/null
+++ b/src/hooks/auto-update-checker/checker.ts
@@ -0,0 +1,119 @@
+import * as fs from "node:fs"
+import * as path from "node:path"
+import type { NpmDistTags, OpencodeConfig, PackageJson, UpdateCheckResult } from "./types"
+import {
+  PACKAGE_NAME,
+  NPM_REGISTRY_URL,
+  NPM_FETCH_TIMEOUT,
+  INSTALLED_PACKAGE_JSON,
+  USER_OPENCODE_CONFIG,
+} from "./constants"
+import { log } from "../../shared/logger"
+
+export function isLocalDevMode(directory: string): boolean {
+  const projectConfig = path.join(directory, ".opencode", "opencode.json")
+
+  for (const configPath of [projectConfig, USER_OPENCODE_CONFIG]) {
+    try {
+      if (!fs.existsSync(configPath)) continue
+      const content = fs.readFileSync(configPath, "utf-8")
+      const config = JSON.parse(content) as OpencodeConfig
+      const plugins = config.plugin ?? []
+
+      for (const entry of plugins) {
+        if (entry.startsWith("file://") && entry.includes(PACKAGE_NAME)) {
+          return true
+        }
+      }
+    } catch {
+      continue
+    }
+  }
+
+  return false
+}
+
+export function findPluginEntry(directory: string): string | null {
+  const projectConfig = path.join(directory, ".opencode", "opencode.json")
+
+  for (const configPath of [projectConfig, USER_OPENCODE_CONFIG]) {
+    try {
+      if (!fs.existsSync(configPath)) continue
+      const content = fs.readFileSync(configPath, "utf-8")
+      const config = JSON.parse(content) as OpencodeConfig
+      const plugins = config.plugin ?? []
+
+      for (const entry of plugins) {
+        if (entry === PACKAGE_NAME || entry.startsWith(`${PACKAGE_NAME}@`)) {
+          return entry
+        }
+      }
+    } catch {
+      continue
+    }
+  }
+
+  return null
+}
+
+export function getCachedVersion(): string | null {
+  try {
+    if (!fs.existsSync(INSTALLED_PACKAGE_JSON)) return null
+    const content = fs.readFileSync(INSTALLED_PACKAGE_JSON, "utf-8")
+    const pkg = JSON.parse(content) as PackageJson
+    return pkg.version ?? null
+  } catch {
+    return null
+  }
+}
+
+export async function getLatestVersion(): Promise<string | null> {
+  const controller = new AbortController()
+  const timeoutId = setTimeout(() => controller.abort(), NPM_FETCH_TIMEOUT)
+
+  try {
+    const response = await fetch(NPM_REGISTRY_URL, {
+      signal: controller.signal,
+      headers: { Accept: "application/json" },
+    })
+
+    if (!response.ok) return null
+
+    const data = (await response.json()) as NpmDistTags
+    return data.latest ?? null
+  } catch {
+    return null
+  } finally {
+    clearTimeout(timeoutId)
+  }
+}
+
+export async function checkForUpdate(directory: string): Promise<UpdateCheckResult> {
+  if (isLocalDevMode(directory)) {
+    log("[auto-update-checker] Local dev mode detected, skipping update check")
+    return { needsUpdate: false, currentVersion: null, latestVersion: null, isLocalDev: true }
+  }
+
+  const pluginEntry = findPluginEntry(directory)
+  if (!pluginEntry) {
+    log("[auto-update-checker] Plugin not found in config")
+    return { needsUpdate: false, currentVersion: null, latestVersion: null, isLocalDev: false }
+  }
+
+  const currentVersion = getCachedVersion()
+  if (!currentVersion) {
+    log("[auto-update-checker] No cached version found")
+    return { needsUpdate: false, currentVersion: null, latestVersion: null, isLocalDev: false }
+  }
+
+  const latestVersion = await getLatestVersion()
+  if (!latestVersion) {
+    log("[auto-update-checker] Failed to fetch latest version")
+    return { needsUpdate: false, currentVersion, latestVersion: null, isLocalDev: false }
+  }
+
+  const needsUpdate = currentVersion !== latestVersion
+  log(`[auto-update-checker] Current: ${currentVersion}, Latest: ${latestVersion}, NeedsUpdate: ${needsUpdate}`)
+
+  return { needsUpdate, currentVersion, latestVersion, isLocalDev: false }
+}
diff --git a/src/hooks/auto-update-checker/constants.ts b/src/hooks/auto-update-checker/constants.ts
new file mode 100644
index 0000000..15c0b63
--- /dev/null
+++ b/src/hooks/auto-update-checker/constants.ts
@@ -0,0 +1,40 @@
+import * as path from "node:path"
+import * as os from "node:os"
+
+export const PACKAGE_NAME = "oh-my-opencode"
+export const NPM_REGISTRY_URL = `https://registry.npmjs.org/-/package/${PACKAGE_NAME}/dist-tags`
+export const NPM_FETCH_TIMEOUT = 5000
+
+/**
+ * OpenCode plugin cache directory
+ * - Linux/macOS: ~/.cache/opencode/
+ * - Windows: %LOCALAPPDATA%/opencode/
+ */
+function getCacheDir(): string {
+  if (process.platform === "win32") {
+    return path.join(process.env.LOCALAPPDATA ?? os.homedir(), "opencode")
+  }
+  return path.join(os.homedir(), ".cache", "opencode")
+}
+
+export const CACHE_DIR = getCacheDir()
+export const VERSION_FILE = path.join(CACHE_DIR, "version")
+export const INSTALLED_PACKAGE_JSON = path.join(
+  CACHE_DIR,
+  "node_modules",
+  PACKAGE_NAME,
+  "package.json"
+)
+
+/**
+ * OpenCode config file locations (priority order)
+ */
+function getUserConfigDir(): string {
+  if (process.platform === "win32") {
+    return process.env.APPDATA ?? path.join(os.homedir(), "AppData", "Roaming")
+  }
+  return process.env.XDG_CONFIG_HOME ?? path.join(os.homedir(), ".config")
+}
+
+export const USER_CONFIG_DIR = getUserConfigDir()
+export const USER_OPENCODE_CONFIG = path.join(USER_CONFIG_DIR, "opencode", "opencode.json")
diff --git a/src/hooks/auto-update-checker/index.ts b/src/hooks/auto-update-checker/index.ts
new file mode 100644
index 0000000..1fd2223
--- /dev/null
+++ b/src/hooks/auto-update-checker/index.ts
@@ -0,0 +1,56 @@
+import type { PluginInput } from "@opencode-ai/plugin"
+import { checkForUpdate } from "./checker"
+import { invalidateCache } from "./cache"
+import { PACKAGE_NAME } from "./constants"
+import { log } from "../../shared/logger"
+
+export function createAutoUpdateCheckerHook(ctx: PluginInput) {
+  let hasChecked = false
+
+  return {
+    event: async ({ event }: { event: { type: string; properties?: unknown } }) => {
+      if (event.type !== "session.created") return
+      if (hasChecked) return
+
+      const props = event.properties as { info?: { parentID?: string } } | undefined
+      if (props?.info?.parentID) return
+
+      hasChecked = true
+
+      try {
+        const result = await checkForUpdate(ctx.directory)
+
+        if (result.isLocalDev) {
+          log("[auto-update-checker] Skipped: local development mode")
+          return
+        }
+
+        if (!result.needsUpdate) {
+          log("[auto-update-checker] No update needed")
+          return
+        }
+
+        invalidateCache()
+
+        await ctx.client.tui
+          .showToast({
+            body: {
+              title: `${PACKAGE_NAME} Update`,
+              message: `v${result.latestVersion} available (current: v${result.currentVersion}). Restart OpenCode to apply.`,
+              variant: "info" as const,
+              duration: 8000,
+            },
+          })
+          .catch(() => {})
+
+        log(`[auto-update-checker] Update notification sent: v${result.currentVersion} → v${result.latestVersion}`)
+      } catch (err) {
+        log("[auto-update-checker] Error during update check:", err)
+      }
+    },
+  }
+}
+
+export type { UpdateCheckResult } from "./types"
+export { checkForUpdate } from "./checker"
+export { invalidateCache } from "./cache"
diff --git a/src/hooks/auto-update-checker/types.ts b/src/hooks/auto-update-checker/types.ts
new file mode 100644
index 0000000..a9a7b19
--- /dev/null
+++ b/src/hooks/auto-update-checker/types.ts
@@ -0,0 +1,22 @@
+export interface NpmDistTags {
+  latest: string
+  [key: string]: string
+}
+
+export interface OpencodeConfig {
+  plugin?: string[]
+  [key: string]: unknown
+}
+
+export interface PackageJson {
+  version: string
+  name?: string
+  [key: string]: unknown
+}
+
+export interface UpdateCheckResult {
+  needsUpdate: boolean
+  currentVersion: string | null
+  latestVersion: string | null
+  isLocalDev: boolean
+}
diff --git a/src/hooks/index.ts b/src/hooks/index.ts
index 07ee565..64d1c6e 100644
--- a/src/hooks/index.ts
+++ b/src/hooks/index.ts
@@ -11,4 +11,5 @@ export { createAnthropicAutoCompactHook } from "./anthropic-auto-compact";
 export { createThinkModeHook } from "./think-mode";
 export { createClaudeCodeHooksHook } from "./claude-code-hooks";
 export { createRulesInjectorHook } from "./rules-injector";
-export { createBackgroundNotificationHook } from "./background-notification";
+export { createBackgroundNotificationHook } from "./background-notification"
+export { createAutoUpdateCheckerHook } from "./auto-update-checker";
diff --git a/src/index.ts b/src/index.ts
index b5fc398..e3b4602 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -14,6 +14,7 @@ import {
   createAnthropicAutoCompactHook,
   createRulesInjectorHook,
   createBackgroundNotificationHook,
+  createAutoUpdateCheckerHook,
 } from "./hooks";
 import {
   loadUserCommands,
@@ -161,6 +162,7 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
   });
   const anthropicAutoCompact = createAnthropicAutoCompactHook(ctx);
   const rulesInjector = createRulesInjectorHook(ctx);
+  const autoUpdateChecker = createAutoUpdateCheckerHook(ctx);
 
   updateTerminalTitle({ sessionId: "main" });
 
@@ -243,6 +245,7 @@ const OhMyOpenCodePlugin: Plugin = async (ctx) => {
     },
 
     event: async (input) => {
+      await autoUpdateChecker.event(input);
       await claudeCodeHooks.event(input);
       await backgroundNotificationHook.event(input);
       await todoContinuationEnforcer(input);