> People follow it closely, because these speedups might be a fluke, and as the compiler becomes more compliant, they may disappear (that happened in past with some JITs).

They're not. YJIT is really 100% compatible with regular interpreter MRI and already run a small % of production traffic at Shopify as well as fully pass the gigantic test suite of Shopify's 10+ years old monolith as well as GitHub's test suite.

This is not a fluke, that's what you get by building a JIT directly inside MRI rather than starting from scratch. It's harder and slower, but you get full compatibility from day 1.