Mistral AI Updates: July 1, 2026

1. Mistral releases Leanstral 1.5 for Lean 4 formal proof engineering

Mistral. Mistral released Leanstral 1.5, an updated Lean 4 model optimized for automated theorem proving and autoformalization. The changelog credits the update with enhanced SFT mixture quality and extended long-context reasoning, and the model card lists 119B total parameters with 6.5B active, a 256k context window, and free access. The release carries a retirement date of September 30, 2026. Source