Mistral's Leanstral 1.5 proves math theorems and finds real bugs in open source code

Formal verification has stayed a niche discipline because writing proofs by hand is brutally slow, so a model that talks directly to the Lean compiler and iterates until a proof checks out could pull rigorous verification into mainstream software engineering. The fact that it found a real bug while just doing math is the detail worth sitting with, since it hints these systems could eventually audit critical code the way they now audit essays. Open weights also mean nobody has to trust the benchmark claims blindly, they can run it themselves.