We didn't want to read colocalsplus directly because we were worried about the stability of that approach and the code complexity / readability. Also, I wasn't aware that colocalsplus would work or if that was lazily populated as well. 

The functions used in CPython to extract the args from colocalsplus do not seem to be public and would need to be reimplemented by PyBind11, right? That seems very brittle as try to support future Python versions and may break in the future.

Having a somewhat stable C-API to query this information seems like it would be the best solution, but I am open to suggestions on how to best proceed. How would you all recommend PyBind11 proceed with supporting 3.11 if not a C-API addition? The PyBind11 authors want to resolve this before the API becomes too locked down for 3.11.