Leanstral 1.5 hits 100% on miniF2F — and catches real bugs
mistral released leanstral 1.5, a lean 4 model that scores 100% on minif2f and catches real rust bugs, signaling that formal verification is now viable for open-source code security.
mistral ai released leanstral 1.5, a free open-source model fine-tuned for the lean 4 language to formalize mathematical proofs and software verification. the model achieves 100% accuracy on the minif2f benchmark and solves 587 problems on putnambench, outperforming all open-source competitors and trailing only aleph prover. in practical tests, it scanned 57 open-source repositories and identified five previously unknown bugs, including a critical overflow in a rust library. this release signals that open-source models are now capable of handling complex formal verification tasks previously reserved for closed systems. available via hugging face and free api, leanstral 1.5 represents a shift toward verifiable, math-grade ai.