Leanstral — Mistral's Open-Source Code Agent for Lean 4 Formal Verification
Mistral has released Leanstral, the first open-source code agent designed specifically for Lean 4, the proof assistant used for formal mathematical and software verification. Released under Apache 2.0, Leanstral uses a sparse 6B active parameter architecture — significantly smaller than competing models — yet outperforms Claude Sonnet on the FLTEval benchmark (26.3 vs 23.7 at pass@2) at a fraction of the cost ($36 vs $549).
Leanstral supports Model Context Protocol (MCP) extensions via lean-lsp-mcp, making it directly operable by AI agents in verification workflows. The model is available through three channels: zero-setup integration via Mistral Vibe with the /leanstral command, a free API endpoint (labs-leanstral-2603), and self-hosted weights for download.
The release also includes FLTEval, a new evaluation suite that goes beyond isolated math problems to tackle realistic formal repository tasks. This positions Leanstral as a key tool in the emerging intersection of agentic AI and formal verification — where agents don't just write code, but prove it correct.
Official announcement: https://mistral.ai/news/leanstral
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Leanstral supports Model Context Protocol (MCP) extensions via lean-lsp-mcp, making it directly operable by AI agents in verification workflows. The model is available through three channels: zero-setup integration via Mistral Vibe with the /leanstral command, a free API endpoint (labs-leanstral-2603), and self-hosted weights for download.
The release also includes FLTEval, a new evaluation suite that goes beyond isolated math problems to tackle realistic formal repository tasks. This positions Leanstral as a key tool in the emerging intersection of agentic AI and formal verification — where agents don't just write code, but prove it correct.
Official announcement: https://mistral.ai/news/leanstral