onEnd not called when stream is aborted

Issue

When using toUIMessageStream with an onEnd callback, the callback may not execute when the stream is aborted. This happens because the abort handler immediately terminates the response, preventing the onEnd callback from being triggered.

// Server-side code where onEnd isn't called on abort
export async function POST(req: Request) {
  const { messages } = await req.json();


  const result = streamText({
    model: "xai/grok-4.6",
    messages: await convertToModelMessages(messages),
    abortSignal: req.signal,
  });


  return createUIMessageStreamResponse({
    stream: toUIMessageStream({
      stream: result.stream,
      onEnd: async ({ isAborted }) => {
        // This isn't called when the stream is aborted!
        if (isAborted) {
          console.log('Stream was aborted');
          // Handle abort-specific cleanup
        } else {
          console.log('Stream completed normally');
          // Handle normal completion
        }
      },
    }),
  });
}

Background

When a stream is aborted, the response is immediately terminated. Without proper handling, the onEnd callback has no chance to execute, preventing important cleanup operations like saving partial results or logging abort events.

Solution

Add consumeSseStream: consumeStream to the createUIMessageStreamResponse configuration. This ensures that abort events are properly captured and forwarded to the onEnd callback, allowing it to execute even when the stream is aborted.

// other imports...
import {
  consumeStream,
  createUIMessageStreamResponse,
  toUIMessageStream,
} from 'ai';


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


  const result = streamText({
    model: "xai/grok-4.6",
    messages: await convertToModelMessages(messages),
    abortSignal: req.signal,
  });


  return createUIMessageStreamResponse({
    stream: toUIMessageStream({
      stream: result.stream,
      onEnd: async ({ isAborted }) => {
        // Now this WILL be called even when aborted!
        if (isAborted) {
          console.log('Stream was aborted');
          // Handle abort-specific cleanup
        } else {
          console.log('Stream completed normally');
          // Handle normal completion
        }
      },
    }),
    consumeSseStream: consumeStream, // This enables onEnd to be called on abort
  });
}