diff --git a/packages/app/src/main.ts b/packages/app/src/main.ts
index 469165ee..fbd921aa 100644
--- a/packages/app/src/main.ts
+++ b/packages/app/src/main.ts
@@ -3,6 +3,7 @@ import { createPinia } from 'pinia'
 import { createRouter, createWebHistory } from 'vue-router'
 import App from './App.vue'
 import './styles/main.css'
+import { initializePlugins } from './plugins'
 
 const router = createRouter({
   history: createWebHistory(),
@@ -23,4 +24,9 @@ const router = createRouter({
 const app = createApp(App)
 app.use(createPinia())
 app.use(router)
+
+initializePlugins().catch((err) => {
+  console.error('[AIUI] Failed to initialize plugins:', err)
+})
+
 app.mount('#app')
diff --git a/packages/app/src/plugins/claude-provider.ts b/packages/app/src/plugins/claude-provider.ts
new file mode 100644
index 00000000..7a627403
--- /dev/null
+++ b/packages/app/src/plugins/claude-provider.ts
@@ -0,0 +1,161 @@
+import type {
+  AIProviderAdapter,
+  AIModel,
+  ChatMessage,
+  ChatOptions,
+  ChatChunk,
+  PluginContext,
+} from '@aiui/core'
+
+const CLAUDE_PATH = '/api/claude/v1/messages'
+
+async function* streamChat(
+  messages: ChatMessage[],
+  options: ChatOptions,
+  systemPrompt?: string,
+): AsyncGenerator<ChatChunk> {
+  const body: Record<string, unknown> = {
+    model: options.model,
+    messages: messages.filter(m => m.role !== 'system').map(m => ({
+      role: m.role,
+      content: typeof m.content === 'string' ? m.content : m.content.map(p => p.text ?? '').join(''),
+    })),
+    stream: options.stream ?? true,
+  }
+
+  // Extract system message from messages or use provided systemPrompt
+  const systemMsg = messages.find(m => m.role === 'system')
+  if (systemPrompt) {
+    body.system = systemPrompt
+  } else if (systemMsg) {
+    body.system = typeof systemMsg.content === 'string'
+      ? systemMsg.content
+      : systemMsg.content.map(p => p.text ?? '').join('')
+  }
+
+  if (options.maxTokens) body.max_tokens = options.maxTokens
+  if (options.temperature !== undefined) body.temperature = options.temperature
+
+  const res = await fetch(CLAUDE_PATH, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(body),
+  })
+
+  if (!res.ok) {
+    const errBody = await res.text().catch(() => 'Could not read error body')
+    yield { type: 'error', error: `Claude proxy error ${res.status}: ${errBody}` }
+    return
+  }
+
+  const reader = res.body?.getReader()
+  if (!reader) {
+    yield { type: 'error', error: 'No response body' }
+    return
+  }
+
+  const decoder = new TextDecoder()
+  let buffer = ''
+
+  try {
+    while (true) {
+      const { done, value } = await reader.read()
+      if (done) break
+
+      buffer += decoder.decode(value, { stream: true })
+      const lines = buffer.split('\n')
+      buffer = lines.pop() ?? ''
+
+      for (const line of lines) {
+        const trimmed = line.trim()
+        if (!trimmed || !trimmed.startsWith('data: ')) continue
+        const payload = trimmed.slice(6)
+        if (payload === '[DONE]') {
+          yield { type: 'done' }
+          return
+        }
+        try {
+          const parsed = JSON.parse(payload)
+          if (parsed.type === 'content_block_delta' && parsed.delta?.text) {
+            yield { type: 'text', text: parsed.delta.text }
+          } else if (parsed.type === 'message_stop') {
+            yield { type: 'done', usage: parsed.usage ? {
+              promptTokens: parsed.usage.input_tokens ?? 0,
+              completionTokens: parsed.usage.output_tokens ?? 0,
+            } : undefined }
+          } else if (parsed.type === 'error') {
+            yield { type: 'error', error: parsed.error?.message ?? 'Claude stream error' }
+          }
+        } catch {
+          // skip malformed chunks
+        }
+      }
+    }
+  } finally {
+    reader.cancel().catch(() => {})
+  }
+
+  yield { type: 'done' }
+}
+
+export const claudeProvider: AIProviderAdapter = {
+  id: 'claude',
+  name: 'Claude (Anthropic)',
+  version: '1.0.0',
+  type: 'ai-provider',
+  description: 'Anthropic Claude AI via proxy server',
+
+  supportsStreaming: true,
+  supportsVision: true,
+  supportsTools: true,
+
+  async init(_context: PluginContext): Promise<void> {
+    // No initialization needed — uses proxy
+  },
+
+  async destroy(): Promise<void> {
+    // No cleanup needed
+  },
+
+  async isAvailable(): Promise<boolean> {
+    try {
+      const res = await fetch(CLAUDE_PATH, { method: 'OPTIONS' })
+      return res.ok || res.status === 405 // OPTIONS may not be supported but proxy is up
+    } catch {
+      return false
+    }
+  },
+
+  chat(messages: ChatMessage[], options: ChatOptions): AsyncIterable<ChatChunk> {
+    return streamChat(messages, options)
+  },
+
+  async models(): Promise<AIModel[]> {
+    return [
+      {
+        id: 'claude-haiku-4.5',
+        name: 'Claude 4.5 Haiku',
+        provider: 'claude',
+        supportsVision: true,
+        supportsTools: true,
+        contextWindow: 200000,
+      },
+      {
+        id: 'claude-sonnet-4',
+        name: 'Claude Sonnet 4',
+        provider: 'claude',
+        supportsVision: true,
+        supportsTools: true,
+        contextWindow: 200000,
+      },
+      {
+        id: 'claude-opus-4',
+        name: 'Claude Opus 4',
+        provider: 'claude',
+        supportsVision: true,
+        supportsTools: true,
+        contextWindow: 200000,
+      },
+    ]
+  },
+}
diff --git a/packages/app/src/plugins/index.ts b/packages/app/src/plugins/index.ts
new file mode 100644
index 00000000..c73669c2
--- /dev/null
+++ b/packages/app/src/plugins/index.ts
@@ -0,0 +1,26 @@
+import { registerPlugin } from '@aiui/core'
+
+export async function initializePlugins(): Promise<void> {
+  // Register built-in AI provider
+  const { claudeProvider } = await import('./claude-provider')
+  registerPlugin(claudeProvider)
+  await claudeProvider.init({
+    settings: {
+      get: () => undefined,
+      set: () => {},
+    },
+    events: {
+      emit: () => {},
+      on: () => () => {},
+    },
+    logger: {
+      info: console.info.bind(console, '[AIUI plugin]'),
+      warn: console.warn.bind(console, '[AIUI plugin]'),
+      error: console.error.bind(console, '[AIUI plugin]'),
+    },
+  })
+
+  if (import.meta.env.DEV) {
+    console.log('[AIUI] Plugins initialized:', claudeProvider.id)
+  }
+}