Leanstral 1.5
#61 in Open-Source-SpraakmodelleMistral AI · v1.5 · 8× · tolest 12. Juli 2026
Leanstral 1.5 is an Open Source language model (Mixture-of-Experts, 119 billion total parameters, approximately 6-6.5 billion active parameters per Token) released by Mistral AI, specifically developed for formal proof verification and code verification in Lean 4. It serves automated theorem proving, autoformalization, and code property verification, and was released under Apache-2.0 license as weights on Hugging Face as well as via a free API. The model achieves state-of-the-art results on Benchmarks such as miniF2F (100%), PutnamBench (587 out of 672), FATE-H (87%), and FATE-X (34%), and was trained through Mid-Training, Supervised Fine-Tuning, and Reinforcement Learning using the CISPO method.
Features
| Key Benchmark (%) | 100% on miniF2F; 87.4% (587/672) on PutnamBench; 87% FATE-H / 34% FATE-X |
| Context Window (Tokens) | 256,000 tokens |
| License | Apache 2.0 |
| Multimodality | Text and image input, text output |
| Platform | Hugging Face (weights), Mistral Labs API, Mistral Vibe, local via vLLM |
| Price per 1M Tokens | $0 (free in Labs tier) |
| Release Date | July 2, 2026 |