Leanstral is the first open-source code agent designed for Lean 4, a proof assistant capable of expressing complex mathematical objects such as perfectoid spaces and software specifications like properties of Rust fragments.

Built as part of the Mistral Small 4 family, it combines multimodal capabilities and an efficient architecture, making it both performant and cost-effective compared to existing closed-source alternatives.

For more details about the model and its scope, please read the related blog post.

Key Features

Leanstral incorporates the following architectural choices:

• MoE: 128 experts, 4 active per token
• Model Size: 119B parameters with 6.5B activated per token
• Context Length: 256k tokens
• Multimodal Input: Accepts text and image input, producing text output

Leanstral offers these capabilities:

• Proof Agentic: Designed specifically for proof engineering scenarios
• Tool Calling Support: Optimized for Mistral Vibe
• Vision: Can analyze images and provide insights
• Multilingual: Supports English, French, Spanish, German, Italian, Portuguese, Dutch, Chinese, Japanese, Korean, and Arabic
• System Prompt Compliance: Strong adherence to system prompts
• Speed-Optimized: Best-in-class performance
• Apache 2.0 License: Open-source license for commercial and non-commercial use
• Large Context Window: Supports up to 256k tokens