useChat No Response | AI SDK 日本語

Issue

I am using useChat. When I log the incoming messages on the server, I can see the tool call and the tool result, but the model does not respond with anything.

Solution

To resolve this issue, convert the incoming messages to the ModelMessage format using the convertToModelMessages function.

import { openai } from '@ai-sdk/openai';
import {
  convertToModelMessages,
  createUIMessageStreamResponse,
  streamText,
  toUIMessageStream,
} from 'ai';

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

  const result = streamText({
    model: 'anthropic/claude-sonnet-5.5',
    messages: await convertToModelMessages(messages),
  });

  return createUIMessageStreamResponse({
    stream: toUIMessageStream({ stream: result.stream }),
  });
}