Leanstral 1.5 AI Model

Mistral has released Leanstral-1.5-119B-A6B, a free Apache-2.0 licensed model with 6B active parameters, showing significant performance upgrades in formal verification. It achieves state-of-the-art results on several benchmarks, including FATE-H and FATE-X.

One continuously updated timeline instead of dozens of separate articles. New developments are appended as the story evolves.

1. ReleaseJul 3, 2026, 02:44 PM 73%

   Mistral Releases Leanstral-1.5-119B-A6B with Significant Performance Upgrades

   Mistral has released Leanstral-1.5-119B-A6B, a free Apache-2.0 licensed model with 6B active parameters, showing significant performance upgrades in formal verification. It achieves state-of-the-art results on several benchmarks, including FATE-H and FATE-X.

   Read the full story →
2. 16 hours later
   ReleaseJul 4, 2026, 07:12 AM 78%

   Mistral AI releases Leanstral 1.5, an open-source model for formal verification in Lean 4

   Mistral AI's Leanstral 1.5, an open-source model, has achieved high scores in formal math benchmarks and identified five unknown bugs in open-source code. The model is designed for formal verification in Lean 4.

   Read the full story →