I usually just say that Go implements "userspace threading", since that's really what it is. Some early, pre-pthreads, implementations of Linux threads worked the same way as Go does and they usually called such implementations "M:N", to indicate M userspace threads mapped onto N kernel threads, so "M:N" is a good descriptor too.

but that's not really accurate. It uses system threads. Userspace threading doesn't make a transition to kernel (IIUC).

Go doesn't need to transition to the kernel to switch threads, does it? It just saves and loads the register state in userland.

IIUC it can, sometimes, avoid a kernel transition when it knows it can schedule the recipient of a message, but I believe that golang creates a threadpool for running goroutines on platforms that use thread primitives.

From https://github.com/golang/go/blob/c7d6c6000a84b61ac8bb2e38e8... I believe "worker threads" are OS threads.