CPython is the past only if you conveniently ignore the entire Scientific Python community, which is a huge use case for Python and depends heavily on C-extensions. Frankly saying a transition to PyPy is &quot;done&quot; when NumPy support is not complete is laughable. Huge Python shops (we&#x27;re talking NASA, CERN, and other institutions on that scale) depend on a Python stack that&#x27;s heavily reliant on a huge range of things, including the C-API, that aren&#x27;t even close to mature in PyPy.