Audience
Engineers and researchers who need an open model for theorem proving, proof debugging, and real-world code verification
About Leanstral 1.5
Leanstral 1.5 is an Apache-2.0 licensed model for practical proof engineering in Lean 4, built to make formal verification more powerful and accessible. With 119B total parameters and only 6B active parameters, it delivers a major performance upgrade for theorem proving, agentic proof engineering, and real-world code verification. Leanstral 1.5 was trained through a three-stage process: mid-training, supervised fine-tuning, and reinforcement learning with CISPO. In the multiturn environment, the model receives a theorem statement, submits a proof, gets Lean compiler feedback, and refines its approach until the proof compiles or the budget is exhausted. In the code agent environment, Leanstral works like a developer in a raw filesystem: it edits files, runs bash commands, and uses the Lean language server to inspect goals, errors, and type information in real time.
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Pricing
Starting Price:
Free
Free Version:
Free Version available.
Integrations
API:
Yes, Leanstral 1.5 offers API access
No integrations listed.
Company Information
Mistral AI
Founded: 2023
France
mistral.ai/news/leanstral-1-5/
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Product Details
Platforms Supported
Cloud
Training
Documentation
Videos
Support
Online
Leanstral 1.5 Frequently Asked Questions
Q: What kinds of users and organization types does Leanstral 1.5 work with?
Leanstral 1.5 works with these users and organization types: Mid Size Business, Small Business, Enterprise, Freelance, Nonprofit, Government, and Startup.
Q: What languages does Leanstral 1.5 support in their product?
Leanstral 1.5 supports these languages: English.
Q: What kind of support options does Leanstral 1.5 offer?
Leanstral 1.5 offers support via online.
Q: Does Leanstral 1.5 have an API?
Yes, Leanstral 1.5 has an API.
Q: What type of training does Leanstral 1.5 provide?
Leanstral 1.5 provides training in the form of documentation and videos.
Q: How much does Leanstral 1.5 cost?
Pricing for Leanstral 1.5 starts at Free.
