lean4

OpenAI claims an internal version of its next major model, Astra, produced solutions to ten mathematical and theoretical computer science problems that had seen no progress in at least a decade. The company says each solution cost less than $2,000 in GPT-5.6 Sol token pricing, and published Lean 4 formalizations along with a paper describing the results.

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.