Registering that I don't expect GPT-5 to be "the biggest model release of the year," for various reasons. I would guess (based on the cost and speed) that the model is GPT-4.1-sized. Conditional on this, the total training compute is likely to be below the state of the art.

For what it's worth, the model showcased in December (then called o3) seems to be completely different from the model that METR benchmarked (now called o3).