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ease
features
design
support

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Description

Leanstral is an open-source AI code agent created by Mistral AI to support formal software verification and mathematical proof development using Lean 4. The system is designed to generate code while simultaneously validating its correctness through formal proof mechanisms. Unlike many AI coding assistants that rely on general-purpose language models, Leanstral is specifically optimized for proof engineering tasks within structured repositories. The model operates using a sparse architecture with efficient active parameters, allowing it to deliver strong performance without requiring extremely large computational resources. Leanstral integrates closely with the Lean proof assistant, which acts as a strict verifier for mathematical reasoning and software specifications. Developers and researchers can use the model to build verified implementations, reducing the need for time-consuming manual debugging and validation. The project is released under the Apache 2.0 open-source license, ensuring accessibility and flexibility for customization. Leanstral also supports integration with model communication protocols, enabling compatibility with development tools and extensions. Benchmarks show that the system can compete with larger closed-source coding agents while maintaining significantly lower operational costs. By combining automated reasoning, code generation, and formal proof verification, Leanstral introduces a new approach to building trustworthy AI-assisted software systems.

Description

Leanstral 1.5 is a model licensed under Apache-2.0, designed for effective proof engineering in Lean 4, aimed at enhancing the capabilities and accessibility of formal verification. It boasts a total of 119 billion parameters, with 6 billion of them being active, marking a significant improvement in performance for tasks such as theorem proving, agent-based proof engineering, and the verification of practical code. The development of Leanstral 1.5 involved a comprehensive three-stage training process, which included mid-training, supervised fine-tuning, and reinforcement learning utilizing CISPO. In a multiturn environment, the model is tasked with receiving a theorem statement, submitting a proof, and refining its approach based on feedback from the Lean compiler until the proof is either successfully compiled or the available resources are depleted. In the code agent setting, Leanstral functions similarly to a developer navigating a raw filesystem, allowing it to edit files, execute bash commands, and interact with the Lean language server to monitor goals, errors, and type information in real time. This innovative approach not only streamlines the proof engineering process but also significantly enhances the user experience in formal verification tasks.

API Access

Has API No 

API Access

Has API Yes 

Screenshots View All

Screenshots View All

Integrations

Mistral AI Yes 
Mistral AI Studio Yes 
Mistral Vibe Yes 

Integrations

Mistral AI No 
Mistral AI Studio No 
Mistral Vibe No 

Pricing Details

Free
Open source
Free Trial No 
Free Version Yes 

Pricing Details

Free
Free Trial No 
Free Version Yes 

Deployment

Web-Based No 
On-Premises Yes 
iPhone App No 
iPad App No 
Android App No 
Windows Yes 
Mac Yes 
Linux Yes 
Chromebook No 

Deployment

Web-Based Yes 
On-Premises No 
iPhone App No 
iPad App No 
Android App No 
Windows No 
Mac No 
Linux No 
Chromebook No 

Customer Support

Business Hours No 
Live Rep (24/7) No 
Online Support No 

Customer Support

Business Hours No 
Live Rep (24/7) No 
Online Support Yes 

Types of Training

Training Docs Yes 
Webinars No 
Live Training (Online) No 
In Person No 

Types of Training

Training Docs Yes 
Webinars No 
Live Training (Online) No 
In Person No 

Vendor Details

Company Name

Mistral AI

Founded

2023

Country

France

Website

mistral.ai

Vendor Details

Company Name

Mistral AI

Founded

2023

Country

France

Website

mistral.ai/news/leanstral-1-5/

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