Would this be unethical if it was a human who heard rumors about a solution then attacked the problem, solved it and published first? Often knowing of the mere existence of a solution carries a lot of information--you would know the problem is accessible, you would expect clues in recent progress (the two Spanish researchers in this case), you would probably have a sense if the solution is a counterexample or positive proof, and so on. I think there are similar examples where we think of them as maybe unsporting but not quite unethical. Does it change if it's openAI and not a human?