How does Rust integrate with the operating system scheduler at runtime level?

Rust itself does not manage scheduling; it relies on OS threads and async runtimes that interface with the OS scheduler.

Rust programs execute on OS threads scheduled by the kernel (Linux CFS, Windows scheduler, etc.). Async runtimes like Tokio multiplex many tasks over a small thread pool. The OS schedules threads preemptively, while Rust async tasks are cooperatively scheduled within those threads. This separation allows Rust to achieve high concurrency without controlling kernel scheduling directly.