Cinder is Meta’s internal high-performance fork built on CPython 3.10.

Cinder has many optimizations for performance, including JIT, lazy loaded modules, precompiled static modules, bytecode inline caching, just-in-time evaluation of coroutines, and an experimental bytecode compiler that uses type annotations to generate Type-specific bytecodes with better performance in the JIT.

Cinder provides backend support for Instagram and is used in a growing number of Python applications in Meta.