In https://docs.python.org/3/c-api/typeobj.html#static-types, it says that PyTypeObject isn't part of the stable ABI. Yet, in https://docs.python.org/3/c-api/type.html#c.PyTypeObject, it says that PyTypeObject IS part of the stable ABI. Which is true?

Thanks for the report! You're right that this is misleading. I'll clarify the docs for this and other structs.

- struct PyTypeObject is part if the limited API.
- its fields and size are not part of the API or stable ABI.

So. According to PEP 384 (which added all structs in the stable ABI, except Py_buffer), some structs are opaque and others have a few members exposed:
https://peps.python.org/pep-0384/#structures

I will split the latter into 1) structs that have a few fields exposed mainly for backwards compatibility (which, of course, is very important here). Best practice is to treat them as opaque (use getters/setters):

- PyObject (ob_refcnt, ob_type)
- PyVarObject (ob_base, ob_size)

... and 2) structs for which all fields are part of the ABI (and the struct's size as well: for most of these as users are expected to provide arrays):

- PyMethodDef
- PyMemberDef
- PyGetSetDef
- PyModuleDefBase
- PyModuleDef
- PyStructSequence_Field
- PyStructSequence_Desc
- PyType_Slot
- PyType_Spec
- Py_buffer (new in 3.11)

The opaque structs continue to be:

- PyThreadState
- PyInterpreterState
- PyFrameObject
- symtable
- PyWeakReference
- PyLongObject
- PyTypeObject

New changeset d79f118d044e9b4244b5dfda35448d39202d7f56 by Petr Viktorin in branch 'main':
bpo-47115: Document which parts of structs are in limited API/stable ABI (GH-32196)
https://github.com/python/cpython/commit/d79f118d044e9b4244b5dfda35448d39202d7f56