To gauge how well the models "think" and what amount of slop they generate.

Keeping it secret because I don't want my answers trained into a model.

Think of it this way, FizzBuzz used to be a good test to weed out bad actors. It's simple enough that any first year programmer can do it and do it quickly. But now everybody knows to prep for FizzBuzz so you can't be sure if your candidate knows basic programming or just memorized a solution without understanding what it does.