New models suddenly doing much better isn't really surprising, especially for this sort of test: going from 98% accuracy to 99% accuracy can easily be the difference between having 1 fatal reasoning error and having 0 fatal reasoning errors on a problem with 50 reasoning steps, and a proof with 0 fatal reasoning errors gets ~full credit whereas a proof with 1 fatal reasoning error gets ~no credit.

And to be clear, that's pretty much all this was: there's six problems, it got almost-full credit on one and half credit on another and bombed the rest, whereas all the other models bombed all the problems.