Cython isn't a separate implementation: it's merely a language that compiles down to CPython API calls. Therefore, it's bound by the GIL insofar as CPython exte

Cython isn't a separate implementation: it's merely a language that compiles down to CPython API calls. Therefore, it's bound by the GIL insofar as CPython extensions are. PyPy does really have a GIL, it's only the experimental PyPy-STM which doesn't.