LLMs & Models5 min read
Lean 4
The $4 theorem prover that embarrasses $300 competitors and found bugs the tests missed
Leanstral 1.5, a 6B active-parameter model, saturates miniF2F, solves 587 PutnamBench problems, and uncovers 5 previously unreported bugs in open-source repositories. At roughly $4 per problem, it undercuts Seed-Prover by 75x and Aleph Prover by 15x, challenging the assumption that formal verification requires massive compute budgets.
2026-07-12