Next.js App Router: stream OpenAI Responses output from a route handler

TL;DR

Route handlers return Response objects. To stream, build a ReadableStream and pump SSE frames into it.

Steps

1. - fetch() the route and read the reader: first frame should arrive in seconds.

• View page source / bundle: the API key must not appear in any client chunk.

When to use

You are seeing this: Route handlers return Response objects. Use this skill when you run into "Next.js App Router: stream OpenAI Responses output from a route handler".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

OpenAI's streaming guide documents the responses.create stream true async-iterator pattern and typed events. Next.js route handlers return Response objects and support ReadableStream bodies; the nodejs runtime export pins server execution for SDK streaming.