Why doesn’t OpenAIStream stream responses with Next.js Assistant Threads?

The short answer is that OpenAIStream isn’t designed to work directly with the beta threads API. OpenAIStream is built to handle real‑time, partial responses from streaming endpoints like the Chat Completions API. Threads, on the other hand, currently work by polling or otherwise retrieving complete responses once the run is finished.

Explanation

• OpenAIStream's purpose:
  OpenAIStream is meant for endpoints that support streaming server-sent events. For example, in a Chat Completions request you can set stream: true to receive chunks of data as they’re generated. OpenAIStream then helps parse and forward those chunks to the client in real time.

• Threads API behavior:
  The threads endpoints work a bit differently. In your code, you’re polling using a loop until the run is complete and then retrieving the messages. This flow means that the entire response is available only once the thread run is finished. Since the threads API doesn’t produce streaming responses the same way, there isn’t any server-sent events stream for OpenAIStream to wrap.

What Can You Do Instead?

If you need real‑time UI updates, you have two options:

1. Keep Polling and Use a Custom Stream:
   You can convert your polling mechanism into a custom ReadableStream on the server. Each time you retrieve new messages from the threads endpoint, you can enqueue those into your stream. For example:

   TYPESCRIPTCopied
   export async function POST(request: Request, response: Response) {
     // Create the thread
     const thread = await openai.beta.threads.create({
       messages: [
         {
           role: "user",
           content: "What are the best Software engineering patterns to use today?",
         },
       ],
     });
     
     // Create the run
     const run = await openai.beta.threads.runs.create(thread.id, {
       assistant_id: config.openAIAssistantId,
     });
     
     // Poll for run completion
     let runStatus = "in_progress";
     while (runStatus === "in_progress") {
       await new Promise((resolve) => setTimeout(resolve, 1000));
       const run_response = await openai.beta.threads.runs.retrieve(thread.id, run.id);
       runStatus = run_response.status;
       // Optionally, enqueue partial messages from a poll if available.
     }
     
     // Retrieve the final messages
     const messages = await openai.beta.threads.messages.list(thread.id);
     
     // Create a custom ReadableStream
     const encoder = new TextEncoder();
     const stream = new ReadableStream({
       start(controller) {
         // Here, you could split messages into chunks for streaming.
         // For simplicity, this example sends the full messages.
         controller.enqueue(encoder.encode(JSON.stringify(messages)));
         controller.close();
       },
     });
     
     return new Response(stream, {
       headers: { "Content-Type": "text/event-stream" },
     });
   }

2. Use an Endpoint with Native Streaming:
   If streaming is crucial, consider using endpoints that support streaming directly (like Chat Completions with stream: true).

Conclusion

To summarize:

• OpenAIStream is not directly usable with threads because the threads API does not natively stream responses.
• If you need streaming-like behavior, you’ll have to implement a custom mechanism (e.g., polling with a ReadableStream) or use a streaming-capable endpoint.

Feel free to ask further questions about setting up custom streams or how to integrate with Next.js!