if we think of them in generations, it seems free ChatGPT is a generation or two behind. I gave a modified river crossing problem to ChatGPT-3, and it failed in the same way, but paid 5.1 doesn't get caught up. exactly where along the way, I'd have to do some digging, but I feel like it was 4.5. The other problem, of course, is that now you've given that question to free ChatGPT, it'll be used as training data, so the next version won't get tripped up the same way.