Later in the same blog post, the author says:

> We can also consider the IMO 2025 problems individually. In the Epoch AI newsletter, Greg Burnham combines a subjective analysis with Evan Chen’s MOHS ratings to argue that the first five problems at IMO 2025 were unusually easy and the sixth was unusually hard, so it’s not surprising that the first five problems were exactly the ones solved by these AIs. Though I’m not sure the MOHS scale is rigorous enough to make sense as the x-axis of a bar chart it’s easy to corroborate the high-level story with the official IMO statistics. Based on average scores, this year’s Problem 6 was the fourth hardest and its Problem 3 was by far the easiest of all Problem 3s and 6s since 2000.

In the linked MaxProof paper, in the section "6.3.1. Per-Problem Analysis" it shows the same behavior: 7/7 in the first 5 problems, 0/7 in the last problem.