Responses stream progressively to the UI

Without progressive streaming, users stare at a frozen interface for the entire generation window, which routinely runs ten to forty seconds on long-context prompts. Abandonment rates on non-streaming chat interfaces regularly exceed fifty percent after ten seconds of dead air. Streaming is the single largest perceived-performance lever in any AI chat product and directly maps to user-experience outcomes; a non-streaming interface feels broken even when the underlying model latency is identical to a streaming competitor.

Return a streaming response from the API route and render it incrementally on the client. With the Vercel AI SDK in app/api/chat/route.ts, call streamText(...) and return result.toDataStreamResponse(); pair it with the useChat hook on the frontend so tokens render as they arrive.

import { streamText } from 'ai';
export async function POST(req: Request) {
  const { messages } = await req.json();
  const result = streamText({ model: openai('gpt-4'), messages });
  return result.toDataStreamResponse();
}