We have multiple CPython core developers at Facebook, and the Cinder team (among others) are heavily involved in discussions around CPython's direction. There are many pieces of Cinder that would never get accepted upstream, or would take a decade of PEPs and incremental improvements to get there. Cinder is both a proof of concept that these ideas can work in CPython, and something that we can use today, rather than waiting a decade to realize these benefits from a pure open source perspective.