The Go Scheduler

How does a Go program run 10,000 goroutines on a computer with 16 logical CPUs, while the operating system sees fewer than 20 threads? Every goroutine needs a CPU core at some point. The operating system, however, schedules threads, and it has never been told that a goroutine exists.

The answer is a scheduler inside every Go program. It belongs to the Go runtime, which is the code the compiler links into each program to manage memory, goroutines, and timers