Our Lean 4 + mathlib project used to spend 41 minutes in CI on every single PR. Today, the worst case — rebuilding the heaviest files from scratch — takes 12 minutes, and an ordinary PR finishes in a few minutes on an incremental build. What we fixed Before After Kernel axiom audit 7m 11s 11s A...
Source: [Dev.to](https://dev.to/iroha1203/taming-a-40-minute-lean-ci-three-rounds-three-wrong-suspects-7ke)