Stream Text with Chat Prompt

Chat completion can sometimes take a long time to finish, especially when the response is big. In such cases, it is useful to stream the chat completion to the client in real-time. This allows the client to display the new message as it is being generated by the model, rather than have users wait for it to finish.

http://localhost:3000

User: How is it going?

Assistant: All good, how may I help you?

Why is the sky blue?

Send Message

Client

Let's create a React component that imports the useChat hook from the ai/react module. The useChat hook will call the /api/chat endpoint when the user sends a message. The endpoint will generate the assistant's response based on the conversation history and stream it to the client.

app/page.tsx

'use client';

import { useChat } from 'ai/react';

export default function Page() {
  const { messages, input, setInput, append } = useChat();

  return (
    <div>
      <input
        value={input}
        onChange={event => {
          setInput(event.target.value);
        }}
        onKeyDown={async event => {
          if (event.key === 'Enter') {
            append({ content: input, role: 'user' });
          }
        }}
      />

      {messages.map((message, index) => (
        <div key={index}>{message.content}</div>
      ))}
    </div>
  );
}

Server

Next, let's create the /api/chat endpoint that generates the assistant's response based on the conversation history.

app/api/chat/route.ts

import { CoreMessage, streamText } from 'ai';
import { openai } from '@ai-sdk/openai';

export async function POST(req: Request) {
  const { messages }: { messages: CoreMessage[] } = await req.json();

  const result = streamText({
    model: openai('gpt-4'),
    system: 'You are a helpful assistant.',
    messages,
  });

  return result.toDataStreamResponse();
}

View Example on GitHub