3Blue1Brown walks through the IMO problem AI models did not solve

Sources: watch, referenced guest post by Grant Sanderson on Terence Tao's blog
Channel: 3Blue1Brown (2026-09-18, 1,018,777 views, 5.0 over 15,507 ratings)
Summary: The video builds the optimal construction, proves that it is optimal, and reaches the Erdos-Szekeres theorem, then closes on what model performance in mathematics does and does not demonstrate. The video description points to a companion post published the same day on Terence Tao's blog, bylined as a guest post by the channel's own creator Grant Sanderson, which reached the Hacker News front page separately.
Why it matters: The worked proof and the closing section give a concrete reference point for claims about model performance on olympiad mathematics.