Agreed. I had wanted the AST to be part of the PEPs specifically *because* it's a public API, but didn't check until today whether or not the original PEP 634 implementation had been merged as-is, or with a cleaned up AST definition.

https://github.com/ncoghlan/cpython/pull/8/files is the initial implementation with the AST and Grammar file updated.

I'll only create the CPython PR once the tests are passing, but I'll try to give Brandt at least a week to review it (I'll also ping him directly via email).