> I've seen it correctly detect AI writing even when people use those "humanizer" rewriting skills

Those skills are meant for humans, not for models. Pangram said in their recent model update that they now also detect the humanizers.

All it requires on their end is running each of their AI outputs through each humanizer and including it in their corpus as ai-humanized.

It's essentially impossible now to prompt your way to non AI detectable text. Even if you do today, it'll be picked up by the next model update.

This is why in academic environments its probably worth re-testing old exams or papers periodically - same way blood and urine samples from athletes are preserved to take advantage of better future testing.

Consider that they are in effect detecting whether text has been generated by one of a few dozen entities that has produced more text for them to analyze than any given human author.

Now imagine if they put the same effort into detecting if a given text was produced by one of a few dozen super-prolific human writers. I'd imagine they'd get pretty good at that too.

The main limitation of those "humanizer" rewriters is that most of them focus on making the next less detectable to humans, by making them read better. There's likely to be plenty of signal left that isn't affected by trying to make the text read better the same way human writers have plenty of idiosyncrasies despite being human.

I agree. I ran it on a small sample last night, basically three paragraphs of AI text that I thought read 100% human, except for em dashes, which I use in writing anyway. It flagged the first and last paras as "high" AI and the middle para as "high" human. I have no idea what it is seeing that sets it off.