(1) Just look at the examples of other builtin types with a similar structure but no free_list.

(2) I guess the intention is for classes that subclass int to also override tp_alloc.

Note that much of this code is written pretty much assuming that subclasses are created using class statements (in a regular Python module, not Cython) which take care of all these details. That doesn't mean Cython is wrong to try this, but it does mean there isn't a lot of documentation, and it also means I don't think the thing you reported qualifies as a bug in CPython.