It's always good to hedge your bets. The two represent the common dichotomy between a reimplementation that potentially reach much higher performance, but will

It's always good to hedge your bets. The two represent the common dichotomy between a reimplementation that potentially reach much higher performance, but will continuously have to battle for compatibility, and an in-tree development that will be limited by backward compatibility etc, but that if merged would be guaranteed to stay up to date. Maxime explains this well in her YJIT talk [0], and it's the same with other languages such as Python, where PyPy is in most cases much faster, but tend to lag a version or two behind. [0] https://www.youtube.com/watch?v=vucLAqv7qpc https://www.youtube.com/watch?v=vucLAqv7qpc