It was and it wasn't. We don't really want to expose it, but if we don't then Cython and other C extensions will access the internal fields directly, which is worse.

Now that we have an unstable API, it should probably be part of that.
I'd like all code object C APIs to be unstable, but it's probably too late for that.

Maybe rename it to PyUnstableCode_GetFirstFree?

Originally posted by @markshannon in #115654 (comment)

Linked PRs

• gh-115756: make PyCode_GetFirstFree an unstable API #115781