What version of Bun is running?

1.3.11-canary.1+9e93bfa1b

What platform is your computer?

Linux 5.10.0-12-amd64 x86_64 x86_64

What steps can reproduce the bug?

Hi

I would like to report a behavior in Bun that can be reproduced using the below Snippet:

import { ReadableStreamBYOBReader } from "node:stream/web";
console.log("ReadableStreamBYOBReader:", ReadableStreamBYOBReader);

What is the expected behavior?

root@KContainer:~/17752# node repro.mjs
ReadableStreamBYOBReader: [class ReadableStreamBYOBReader]

What do you see instead?

In Node.js and Deno, ReadableStreamBYOBReader from node:stream/web is a native class.
In Bun, it is exposed as a plain Function, breaking class identity and stream compatibility checks.

root@KContainer:~/git/run/cerebras/deno/OPENAI/gpt5.1/filter/batch_2/cross_runtime/temp_node/17752# bun run repro.mjs
ReadableStreamBYOBReader: [class Function]

If a library does:
if (value instanceof ReadableStreamBYOBReader)
It will fail in Bun.

Additional information

No response