Leanstral 1.5 Open-Sourced for Lean 4
sophiamyang · x · 2026-07-04
Sophia Yang releases Leanstral 1.5, a 119B (6B activation) open-source model designed for Lean 4 formal theorem proving. It achieves SOTA on miniF2F with 100%, PutnamBench with 587/672 (approx. $4/problem), FATE-H with 87%, and FATE-X with 34%, while discovering 5 previously unknown bugs in real open-source projects. It is licensed under Apache-2.0, with weights hosted on HuggingFace and a free API provided.
Related event: Mistral Releases Open-Source Lean 4 Proving Agent Leanstral 1.5(5 posts)→
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