convertToModelMessages()

The convertToModelMessages function is used to transform an array of UI messages from the useChat hook into an array of ModelMessage objects. These ModelMessage objects are compatible with AI core functions like streamText.

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

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

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

  return result.toUIMessageStreamResponse();
}

Import

import { convertToModelMessages } from "ai"

API Signature

Parameters

Returns

An array of ModelMessage objects.

Multi-modal Tool Responses

The convertToModelMessages function supports tools that can return multi-modal content. This is useful when tools need to return non-text content like images.

import { tool } from 'ai';
import { z } from 'zod';

const screenshotTool = tool({
  parameters: z.object({}),
  execute: async () => 'imgbase64',
  toModelOutput: result => [{ type: 'image', data: result }],
});

const result = streamText({
  model: openai('gpt-4'),
  messages: convertToModelMessages(messages, {
    tools: {
      screenshot: screenshotTool,
    },
  }),
});

Tools can implement the optional toModelOutput method to transform their results into multi-modal content. The content is an array of content parts, where each part has a type (e.g., 'text', 'image') and corresponding data.