Streaming in Next.js (Pages) API routes not working

[giuseppeg]

Summary

Update: Vercel confirmed that the docs were wrong and streaming is not supported in the Next.js pages.

I have a Next.js (pages) API route (Node.js handler) and want to stream some data but streaming doesn't work.

According to https://vercel.com/docs/functions/streaming#streaming-functions it should just work.

I am setting the route config supportsResponseStreaming flag to true but streaming doesn't work on Vercel. It however seems to be working locally (npm run dev or vercel dev).

Additional information

On Vercel the API route buffers the response and flushes only at the end when the connection is closed with res.end().

Example

Source: https://gist.github.com/giuseppeg/ae8150a53c5caea8b88f8283ea63b6d3
Deployment: https://test-node-streaming-seven.vercel.app

[SalmenBejaoui]

The streaming works only with the App Router.

[giuseppeg]

Yes that seems the case but this is a pages router app and issue and I would like to figure out why streaming doesn't work there.

The docs suggest that the Node js handler in pages router should work when the supportsResponseStreaming is true https://vercel.com/docs/functions/streaming#streaming-functions

and there is a discrepancy between development and production (Vercel). It'd be great if someone from the team could clarify as I am trying to avoid a refactoring if possible.

Perhaps it indeed works only with App Router but the docs are wrong or out to date?

[giuseppeg]

Thanks @SLMNBJ. Vercel confirmed that the docs were wrong and streaming is not supported in the Next.js pages.