Cython does work with pypy, but via the cpyext emulation of the CPython C API. See this answer from one of the pypy devs when I asked about this about a year ag

Cython does work with pypy, but via the cpyext emulation of the CPython C API. See this answer from one of the pypy devs when I asked about this about a year ago: https://news.ycombinator.com/item?id=10195892 https://news.ycombinator.com/item?id=10195892 Maybe cpyext has gotten faster since then, but I think that's the state of things still.