assistant-ui--assistant-ui/examples/with-cloud-standalone/app/api/chat/route.ts

import { openai } from "@ai-sdk/openai";
import { streamText, convertToModelMessages } from "ai";
import type { UIMessage } from "ai";

export const maxDuration = 30;

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

  const result = streamText({
    model: openai("gpt-5.4-nano"),
    messages: await convertToModelMessages(messages),
  });

  return result.toUIMessageStreamResponse({
    messageMetadata: ({ part }) => {
      if (part.type === "finish") {
        return {
          usage: part.totalUsage,
        };
      }
      if (part.type === "finish-step") {
        return {
          modelId: part.response.modelId,
        };
      }
      return undefined;
    },
  });
}