> I guess if patch-level Python releases break ABI, that's an upstream bug
It's not about breaking the ABI so much as about bugs getting fixed in CPython point releases, for example. Cython generated C code will typically stop working around them if you build on a later version, so that the work-around will be gone if you then try to run the binary module on an older point version that has the bug. It's this kind of subtle issues that I'd hate to push users into (and thus myself, because if they come complaining, then it takes time on both sides to debug it).
> I guess if patch-level Python releases break ABI, that's an upstream bug
It's not about breaking the ABI so much as about bugs getting fixed in CPython point releases, for example. Cython generated C code will typically stop working around them if you build on a later version, so that the work-around will be gone if you then try to run the binary module on an older point version that has the bug. It's this kind of subtle issues that I'd hate to push users into (and thus myself, because if they come complaining, then it takes time on both sides to debug it).