> how are they going to do this while making sure programs are still correct? So much existing multithreaded Python code is written in an unsafe manner.

a) How is it the python maintainers job to make sure unsafe code runs correctly?

b) The GIL doesn't prevent data races. Simple as that. It keeps the internal running of the interpreter sane, that's it's only job. There is a reason the threading library has a plethora of lock-classes