It seems like they threw it a decently large battery of open math problems and probably limited it to something like $200-500 per problem:

https://x.com/polynoamial/status/2083478171975082334

As a complete guess, it seems like they tested hundreds to thousands of problems with a relatively low per-problem budget

--

The linked tweet from Noam Brown at OpenAI reads:

> And yes we did try other major problems without success. Sadly no Millennium Prize problems (yet).

> But also, we didn’t spend a lot on each problem. It’s possible to push test-time compute much further.