Leanstral 1.5: Mistral AI's New Math Code Model Explained

Mistral AI has released Leanstral 1.5, a new model for writing and checking Lean 4 math code. This model is open under the Apache 2.0 license, allowing developers to use it with fewer limits. On the PutnamBench test, Leanstral 1.5 solved 587 out of 672 problems, achieving an 87.4% solve rate. This model writes formal proofs, which are step-by-step math arguments a computer can test. Computers can check each step, making the results more reliable than a normal text answer. Formal proof tools can help verify hard logic in areas like chips, software, and security. This release puts a new focus on open math AI tools.