Streaming Not Working When Deploying on Vercel (Next.js Pages Router)

Issue

I'm using the Next.js Pages Router. Streaming with the AI SDK works in my local development environment. However, when deploying to Vercel, streaming does not work in the deployed app. Instead of streaming, only the full response is returned after a while.

Cause

The Next.js Pages Router currently does not support streaming with its own routes.

Solution

With Next.js 13+, you can mix and match App Router and Pages Router routes in the same project. You need to use App Router routes for streaming with the AI SDK.

Example App Router route:

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

// Force the route to be dynamic and allow streaming responses up to 30 seconds
export const dynamic = 'force-dynamic';
export const maxDuration = 30;

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

  const result = streamText({
    model: openai('gpt-4-turbo'),
    messages,
  });

  return result.toDataStreamResponse();
}