As a heavy user of the non-limited Python C API, I would like to offer my suggestions for consideration.  (I'm not allowed to post in discourse)

First off, to me, 'unstable' comes off quite negative, i.e. risky or erratic.  Brett's suggestion of 'broad' is, well, seemingly too "broad" :)

In no particular order, some ideas:

- 'extended' or 'extra'; as opposed to limited (from the macro)

- 'volatile'; synonym for 'unstable' but with the benefit of being a C concept.  I like this one as the APIs covered by this include would have access to the "volatile" object details.  Things like borrowed references, direct array access or even the structure fields of the objects themselves.

- 'crunchy'; Monty Python reference, "If we took the bones out, it wouldn't be crunchy, would it?"
  https://en.wikipedia.org/wiki/Crunchy_Frog