How do you imagine async works otherwise? Also, in case you misunderstand how polling works in practice in rust, it's not polling in the traditional web development sense where it polls every 5 ms to check if a future is completed (although you can do this if you want to for some reason). There are typically "wakers" that are "awoken" by the os when data is ready and when they are "awoken" then they poll. And since they are only awoken by the OS when the information is ready it really never has to poll more than once unless there are multiple bundled futures.

I don't want to "well actually" the "well actually", but I think you missed the word syntactically.

> C#'s Task/Task<T> are based on background execution. Once something is awaited, control is returned to the caller.

Async/await in any language happens in the background.

What happens during a Task.Yield() (C#)? The task is yielded to the another awaiting task in the work queue. Same as Rust.

> OTOH, Rust's Future<T> is, by default, based on polling/stepping,

The await syntax abstracts over Future/Stream polling. The real difference is that Rust introduced the Future type/concept of polling at all (which is a result of not having a standard async runtime). There is a concept of "is this task available to proceed on" in C# too, it's just not exposed to the user and handled by the CLR.