I am not saying stackful coroutines are bad, I'am using Go on daily basis, I've used libmill stackfull coroutines in C etc. They have their usage cases in which they will be better than stackless coroutines, there are tradeoffs in both designs of coroutines. Stackless coroutines for my use case they are ideal (async IO) and can be easily optimized. I don't agree with what you wrote about using coroutines (and similar concepts) for async completion is niche. In most code bases I saw coroutines/tasks/gorutines etc are used mainly for async IO.