tech
Leanstral 1.5: Proof Abundance for All
Leanstral 1.5, a free Apache-2.0 licensed model with 6B active parameters, delivers a major performance upgrade in formal verification, saturating miniF2F, solving 587/672 PutnamBench problems, and achieving state-of-the-art results on FATE-H (87%) and FATE-X (34%). Trained through mid-training, supervised fine-tuning, and reinforcement learning with CISPO, it excels in agentic proof engineering and real-world code verification, uncovering 5 previously unknown bugs across 57 repositories tested. Fully open-sourced and available via Hugging Face and a free API, Leanstral 1.5 is now accessible for practical proof engineering in Lean 4.
TL;DR
- Leanstral 1.5 is a free, Apache-2.0 licensed model with 6B active parameters.
- It achieves major performance upgrades in formal verification, saturating miniF2F and solving a high percentage of PutnamBench problems.
- The model demonstrates state-of-the-art results on FATE-H (87%) and FATE-X (34%).
- Training involved mid-training, supervised fine-tuning, and reinforcement learning with CISPO.
- It excels in agentic proof engineering and real-world code verification, discovering 5 unknown bugs in 57 repositories.
- Leanstral 1.5 is fully open-sourced and available via Hugging Face and a free API for use in Lean 4.
- The model is now accessible for practical proof engineering.