22 days ago
- Leanstral 1.5 is a free Apache-2.0 licensed model with 6B active parameters, offering a significant performance upgrade in formal verification.
- It achieves state-of-the-art results on benchmarks: 100% on miniF2F, 587/672 on PutnamBench, 87% on FATE-H, and 34% on FATE-X.
- The model undergoes a three-stage training process: mid-training, supervised fine-tuning, and reinforcement learning with CISPO, using multiturn and code agent environments.
- It demonstrates strong test-time scaling on PutnamBench, solving more problems as token budget increases, from 44 at 50k tokens to 587 at 4M tokens.
- Leanstral 1.5 excels in code verification, proving time complexity for AVL trees and uncovering 5 previously unknown bugs across 57 repositories tested.
- The model is fully open-sourced and available via Hugging Face and a free API, with recommendations for setup using Mistral Vibe and Lean LSP MCP.