Sure, but that overhead is also not essential, but a feature of Go's particular implementation. Fibers aren't one thing and there are many, many ways of implementing them. As I said before, implementing them for Rust well would have likely required changes to LLVM and Web Assembly, and even then it would be harder than async/await, perhaps to the point of being too hard to be worth it and probably against aspects of Rust's philosophy (I would say that that is the main difference between the two: achieving similar performance is much easier for the language implementors with async/await). But it's just not true that there is something essential about them that makes them slower. After all, you're running all of your code inside a particular implementation of threads.