C++20 coroutines are not async in the standard. They are just coroutines. Actually they have no implementation. The user has to write classes to implement the promise type and the awaitable type. You could just as easily write a coroutine library wrapping epoll as you could io_uring. The only thing it does behind your back (other than compile to stackless coroutines) is allocate memory, which also goes for a lot of other things.