[zurn]

I have to confess to not actually being a Rust user. But, isn't for example std::io used by most Rust programs?

[Rusky]

std::io doesn't use a runtime, it just makes system calls directly.

(It used to use a runtime because it had optional M:N threading, but that was removed when it turned out not to be any faster than 1:1 threading, caused all sorts of problems with stack switching, and of course pulled in a problematic runtime.)