[pkulak]

Java 21, and I assume like every scripting language (Ruby, Python, etc). Though I guess with scripting you can't use more than one OS thread (not totally sure). Rust started off with it, and C# tried it too, but there are huge downsides to the model, so it's not like it's perfection incarnate and every other language just can't pull it off.

[smw]

Does 21 actually automatically schedule fibers? to open cores?

[pkulak]

Yup. It's all 100% automatic. Just use a different name for the thread pool and you're done, I believe.