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createUIMessageStreamResponse

The createUIMessageStreamResponse function creates a Response object that streams UI messages to the client.

Import

import { createUIMessageStreamResponse } from "ai"

Example

import {
  createUIMessageStream,
  createUIMessageStreamResponse,
  streamText,
  toUIMessageStream,
} from 'ai';

const response = createUIMessageStreamResponse({
  status: 200,
  statusText: 'OK',
  headers: {
    'Custom-Header': 'value',
  },
  stream: createUIMessageStream({
    execute({ writer }) {
      // The outer stream owns the assistant message lifecycle.
      writer.write({ type: 'start' });

      // Write custom data (type must be 'data-<name>')
      writer.write({
        type: 'data-message',
        data: { content: 'Hello' },
      });

      // Write text content using start/delta/end pattern
      writer.write({
        type: 'text-start',
        id: 'greeting-text',
      });
      writer.write({
        type: 'text-delta',
        id: 'greeting-text',
        delta: 'Hello, world!',
      });
      writer.write({
        type: 'text-end',
        id: 'greeting-text',
      });

      // Write source information (flat properties, not nested)
      writer.write({
        type: 'source-url',
        sourceId: 'source-1',
        url: 'https://example.com',
        title: 'Example Source',
      });

      // Merge with LLM stream
      const result = streamText({
        model: 'anthropic/claude-sonnet-5.5',
        prompt: 'Say hello',
      });

      writer.merge(
        toUIMessageStream({ stream: result.stream, sendStart: false }),
      );
    },
  }),
});

API Signature

Parameters

  • stream (ReadableStream<UIMessageChunk>): The UI message stream to send to the client.
  • status? (number): The status code for the response. Defaults to 200.
  • statusText? (string): The status text for the response.
  • headers? (Headers | Record<string, string>): Additional headers for the response.
  • keepAliveMs? (number): Interval in milliseconds for sending SSE keep-alive comments. When set, an opening comment is sent immediately and additional comments are sent after the stream has been idle for the configured interval.
  • consumeSseStream? ((options: { stream: ReadableStream<string> }) => PromiseLike<void> | void): Optional callback to consume the Server-Sent Events stream.

Returns

Response

A Response object that streams UI message chunks with the specified status, headers, and content.

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