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MODEL · ENTITY #2582

Leanstral

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2

MODELS · 1 SOURCE · Mistral AI

Leanstral 1.5: open-source 6B-active-parameter model advances formal verification

Leanstral 1.5 is an Apache-2.0 open-source model (119B total, 6B active parameters) released for Lean 4 proof engineering; it uses mid-training, supervised fine-tuning, and reinforcement learning with CISPO and is available via Hugging Face and a free API. The model saturates miniF2F, solves 587/672 PutnamBench problems, achieves 87% on FATE-H and 34% on FATE-X, scales strongly with token budget, improves FLTEval pass rates, and found 5 previously unknown bugs across 57 tested repositories.

8.0

MODELS · 1 SOURCE · Mistral AI

Leanstral: open-source Lean 4 proof-engineering agent (Leanstral-120B-A6B) released under Apache 2.0

Leanstral, an open-source code agent trained for Lean 4 proof engineering and shipped as Leanstral-120B-A6B, is released with Apache 2.0 weights, an agent mode for Mistral vibe, a free API endpoint, a forthcoming tech report, and a new evaluation suite called FLTEval. The model uses a highly sparse architecture (6B active parameters), supports MCPs via vibe (optimized for lean-lsp-mcp), and is benchmarked on realistic repository tasks where it shows cost and efficiency advantages versus several closed- and open-source competitors.

8.0