Leanstral 1.5: Proof Abundance for All
Summary
Mistral AI has released Leanstral 1.5, an open source AI model that significantly improves formal verification and agent-based proof engineering performance in Lean 4 environments.
Key Points
- It is a free and open source model under the Apache-2.0 license with 6B active parameters out of a total of 119B parameters.
- It underwent mid-training, supervised fine-tuning (SFT), and CISPO reinforcement learning, and was trained in a multi-turn environment with Lean compiler feedback and a code agent environment handling the file system and bash commands.
- By testing 57 actual open source repositories, we found 5 errors that had not been found before, proving our ability to use it in practice.
Notable Quotes & Details
Notable Data / Quotes
- 6B active parameters
- 587/672 PutnamBench
- 87% on FATE-H
- 34% on FATE-X
- 5 previously unknown bugs across 57 repositories tested
- 119B total parameters
Intended Audience
Mathematics researchers, formal validation experts, software agent developers, and Lean 4 users.