Python threads are built on top of "real" preemptive OS threads. The presence of the GIL does not change that. GIL can be released and it is released e.g., for

Python threads are built on top of "real" preemptive OS threads. The presence of the GIL does not change that. GIL can be released and it is released e.g., for IO, during heavy computations in C extensions--Python program can utilize multiple CPU cores.