Yeah it was just a mistake we made in the API design in 2019. You can’t extend a struct and assume embedding people all rebuild. They don’t. Real world embedding uses exist that use an installed Python minor version as a shared library. Update that to use a different sized struct in a public API and someone is going to have a bad time. That’s why I consider the struct frozen at rc1 time, even when only for use in the embedding / writing their own launcher case.