What is the real execution model of Kotlin coroutines inside JVM threads?

Coroutines are state machines executed on JVM threads managed by dispatchers.

Kotlin coroutines are compiled into continuation-passing state machines. Each suspend function is transformed into a state machine that stores execution state. When suspension occurs, the function returns control to the dispatcher, freeing the thread. On resumption, execution continues from the saved state. This makes coroutines extremely lightweight compared to threads, enabling millions of concurrent tasks.