Mistral Leanstral 1.5: an open proof model that solved 587 Putnam problems
AnalysisFormal proof engineering, the slow work of getting a computer to verify that a piece of math or code is provably correct, just got a capable free tool. Mistral released Leanstral 1.5 on July 2 under an Apache-2.0 license (free to use, modify, and sell), built for Lean 4, a language for writing machine-checkable proofs. It solved 587 of 672 problems from the Putnam undergraduate math competition and scored 100% on the miniF2F benchmark. Pointed at real repositories, it surfaced five previously unknown bugs. The model carries 119 billion parameters but fires only 6 billion per query, which keeps it cheap to run.