It will be tough to draw the line, as the meat brains trying to prove it were also using AI.
I assume that the mathematicians outside Anthropic were hoping to publish an actual human-understandable paper. That could be one way to draw line: you can use AI, but you must also have an intelligible explanation at the end.
Yes, but it took far less than using your meat brain to prove the Navier-Stokes Clay problem.