Open, the site's label. The exact maximum $t(N)$ is not known for general $N$. The refereed bounds are recorded as accepted partial claims on the claim pages of Simonovits and Sós and Szabó, and Yang's reported exact values for $3\leq N\leq12$ as a claimed partial claim on his. Szabó's linear-error question, whether $t(N)=N^2/2+O(N)$ (the second of the two questions in Section 6 of his 1999 paper), has an affirmative Lean proof that the bounty site Conjectures.io verified on 9 September 2026 and approved; that settles a variant, not the catalog question, and is recorded as an accepted partial claim on its claim page (JenW1N, 2026) (see Current assessment).