My suspicion (unconfirmed so take it with a grain of salt) is they either used some/all test data to train, or there was some leakage from the benchmark set into their training set.

That said Sonnet 4.5 isn’t new and there have been loads of innovations recently.

Exciting to see open models nipping at the heels of the big end of town. Let’s see what shakes out over the coming days.