Mistral Small 4 (119B-2603) + Leanstral: First Code Agent Designed for Lean 4 Formal Proofs

Mistral AI·medium signal

Mistral AI released Mistral Small 4, a 119B-parameter MoE model with an NVFP4 quantized variant co-developed with NVIDIA. In the same drop, Mistral released Leanstral-2603 — the first open-source code agent designed specifically for Lean 4, the formal proof assistant used to express mathematical structures like perfectoid spaces. Leanstral extends the code agent paradigm into formal verification, a domain where LLM hallucinations have historically been disqualifying.