proof-assistant

Mistral AI has released Leanstral, a sparse 120B model with 6B active parameters designed specifically for the Lean 4 proof assistant. The model is available under Apache 2.0 license with free API access and achieves a 26.3 FLTEval score at pass@2, outperforming Claude Sonnet 4.6 while costing $36 versus $549.

Mistral AI released Leanstral, the first open-source code agent designed specifically for Lean 4 formal proof verification. The model uses 6B active parameters in a sparse 120B architecture and is available under Apache 2.0 license with free API access.