npm install @tanstack/ai @tanstack/ai-react @tanstack/ai-openai

import { chat, toServerSentEventsResponse } from "@tanstack/ai";
import { openaiText } from "@tanstack/ai-openai";

export async function POST(request: Request) {
  const { messages } = await request.json();
  const stream = chat({
    adapter: openaiText("gpt-5.2"),
    messages,
  });
  return toServerSentEventsResponse(stream);
}

import { useState } from "react";
import { useChat, fetchServerSentEvents } from "@tanstack/ai-react";

export function Chat() {
  const [input, setInput] = useState("");
  const { messages, sendMessage, isLoading } = useChat({
    connection: fetchServerSentEvents("/api/chat"),
  });

  return (
    <div>
      {messages.map((message) => (
        <div key={message.id}>
          <strong>{message.role}:</strong>
          {message.parts.map((part, idx) => {
            if (part.type === "text") return <span key={idx}>{part.content}</span>;
            if (part.type === "thinking") return <em key={idx}>{part.content}</em>;
            return null;
          })}
        </div>
      ))}
      <form onSubmit={(e) => { e.preventDefault(); sendMessage(input); setInput(""); }}>
        <input value={input} onChange={(e) => setInput(e.target.value)} disabled={isLoading} />
        <button type="submit" disabled={isLoading}>Send</button>
      </form>
    </div>
  );
}

const {
  messages,          // UIMessage[] — current messages
  sendMessage,       // (content: string | MultimodalContent) => Promise<void>
  append,            // (message: ModelMessage | UIMessage) => Promise<void>
  isLoading,         // boolean
  error,             // Error | undefined
  stop,              // () => void — cancel current stream
  reload,            // () => Promise<void> — regenerate last response
  clear,             // () => void — clear all messages
  setMessages,       // (messages: UIMessage[]) => void
  addToolResult,     // (result: { toolCallId, tool, output, state? }) => Promise<void>
  addToolApprovalResponse, // (response: { id, approved }) => Promise<void>
} = useChat({
  connection: fetchServerSentEvents("/api/chat"),
  tools?,             // client tool implementations
  initialMessages?,   // UIMessage[]
  id?,                // string — unique chat instance id
  body?,              // additional body params sent with every request
  onResponse?,        // (response) => void
  onChunk?,           // (chunk) => void
  onFinish?,          // (message) => void
  onError?,           // (error) => void
});

interface UIMessage {
  id: string;
  role: "user" | "assistant";
  parts: (TextPart | ThinkingPart | ToolCallPart | ToolResultPart)[];
}

import { fetchServerSentEvents, fetchHttpStream, stream } from "@tanstack/ai-react";

// SSE (recommended — auto-reconnection)
fetchServerSentEvents("/api/chat", { headers: { Authorization: "Bearer token" } })

// HTTP stream (NDJSON)
fetchHttpStream("/api/chat")

// Custom
stream(async (messages, data, signal) => { /* return async iterable */ })

import { openaiText } from "@tanstack/ai-openai";       // openaiText('gpt-5.2')
import { anthropicText } from "@tanstack/ai-anthropic";  // anthropicText('claude-sonnet-4-5')
import { geminiText } from "@tanstack/ai-gemini";        // geminiText('gemini-2.5-pro')
import { ollamaText } from "@tanstack/ai-ollama";        // ollamaText('llama3')
import { grokText } from "@tanstack/ai-grok";            // grokText('grok-4')
import { openRouterText } from "@tanstack/ai-openrouter"; // openRouterText('openai/gpt-5')

import { toolDefinition } from "@tanstack/ai";
import { z } from "zod";

const getWeatherDef = toolDefinition({
  name: "get_weather",
  description: "Get current weather for a location",
  inputSchema: z.object({ location: z.string() }),
  outputSchema: z.object({ temperature: z.number(), conditions: z.string() }),
  needsApproval: false, // optional
});

// Server implementation — runs on server with DB/API access
const getWeather = getWeatherDef.server(async ({ location }) => {
  const data = await fetchWeather(location);
  return { temperature: data.temp, conditions: data.conditions };
});

// Client implementation — runs in browser for UI/localStorage
const getWeatherClient = getWeatherDef.client((input) => {
  return { temperature: 72, conditions: "cached" };
});

import { clientTools, createChatClientOptions, type InferChatMessages } from "@tanstack/ai-client";

const tools = clientTools(updateUI, saveToStorage); // no 'as const' needed
const chatOptions = createChatClientOptions({
  connection: fetchServerSentEvents("/api/chat"),
  tools,
});
type ChatMessages = InferChatMessages<typeof chatOptions>;

// In component:
const { messages } = useChat(chatOptions);
// messages typed — part.name is discriminated union, part.input/output typed from Zod schemas

npm install -D @tanstack/react-ai-devtools @tanstack/react-devtools

import { TanStackDevtools } from "@tanstack/react-devtools";
import { aiDevtoolsPlugin } from "@tanstack/react-ai-devtools";

<TanStackDevtools
  plugins={[aiDevtoolsPlugin()]}
  eventBusConfig={{ connectToServerBus: true }}
/>