Leanstral 1.5: Proof Abundance for All

What this post added

This post introduces Leanstral 1.5, a new formal verification model. It details the three-stage training process (mid-training, supervised fine-tuning, reinforcement learning with CISPO) and the two RL environments used: a multiturn environment for theorem proving and a code agent environment for real-world code verification. The post also presents evaluation results on miniF2F, PutnamBench, FATE-H, FATE-X, and FLTEval, highlighting performance improvements and cost efficiency. Case studies on AVL tree time complexity verification and bug discovery in open-source repositories are included. Instructions for getting started with Leanstral 1.5 via Hugging Face, a free API, and Mistral Vibe are provided.