Leanstral

Name: Leanstral
Author: Mistral AI

Mistral AI🇫🇷 France

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Version History

120B-A6BmajorMay 28, 2026

First release of Leanstral, an open-source code agent specialized for Lean 4 formal verification with 120B total parameters and 6B active parameters.

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model releaseMistral AI

Mistral releases Leanstral, 6B-parameter open-source model for Lean 4 formal proof verification

Mistral AI released Leanstral, the first open-source code agent designed specifically for Lean 4 formal proof verification. The model uses 6B active parameters in a sparse 120B architecture and is available under Apache 2.0 license with free API access.

May 28, 2026 · 10:06 AM3 min read

mistral-ai leanstral formal-verification

analysis

Mistral's Leanstral code verification agent outperforms Claude Sonnet at 15% of the cost

Mistral has released Leanstral, a 120B-parameter code verification agent built with the Lean programming language, claiming it outperforms larger open-source models and offers significant cost advantages over Anthropic's Claude suite. The model achieves a pass@2 score of 26.3—beating Claude Sonnet by 2.6 points—while costing $36 to run compared to Sonnet's $549.

March 17, 2026 · 7:05 PM2 min read

mistral-ai code-generation formal-verification