Leanstral: Open-source agent for trustworthy coding and formal proof engineering

Lean 4 paper (2021): https://dl.acm.org/doi/10.1007/978-3-030-79876-5_37

https://mistral.ai/news/leanstral

Curious if anyone else had the same reaction as me

This model is specifically trained on this task and significantly[1] underperforms opus.

Opus costs about 6x more.

Which seems... totally worth it based on the task at hand.

[1]: based on the total spread of tested models

Agreed. The idea is nice and honorable. At the same time, if AI has been proving one thing, it's that quality usually reigns over control and trust (except for some sensitive sectors and applications). Of course it's less capital-intense, so makes sense for a comparably little EU startup to focus on that niche. Likely won't spin the top line needle much, though, for the reasons stated.
Treating "quality" as something you can reliably measure in AI proof tools sounds nice until you try auditing model drift after the 14th update and realize the "trust" angle stops being a niche preference and starts looking like the whole product. Brand is not a proof. Plenty of orgs will trade peak output for auditability, even if the market is bigger for YOLO feature churn.