Mistral AI Releases Leanstral 1.5 for Formal Proof Generation

Jul 10, 2026

Mistral AI has released Leanstral 1.5, a model fine-tuned from Mistral Large 3.1 to generate formal proofs in the Lean theorem prover. The model achieves a 40% pass rate on the Lean 4 version of the ProofNet benchmark, surpassing GPT-4o and Claude 3.5 Sonnet. Leanstral 1.5 is available under the Mistral Research License for non-commercial use.

Why it matters: This release advances AI-assisted formal verification, which is critical for ensuring correctness in mathematics and software.

Full story at: Mistral AI News ↗