Umm, yes it does? For the longest time, Guido’s defense for the GIL was that all previous efforts resulted in an unacceptable hit to single threaded performance.
From when I was reading the proposal, the idea is that until a C extension is loaded, you can assume that there are no other threads. Then when a module is loaded, by default you assume that it uses threads but modules that are thread free can indicate that using a flag, so if a module indicates it's thread free then you continue running without the thread safety features.
