It really isn't and it's sad seeing so many people say it so confidently on this site. It only detects plain / basic prompted stuff. "write me an essay on x", sure. The moment you prompt it differently, it stops working. Add "output should be STE100 compliant" or something to your prompts and detection goes away. Fine-tune any local llm on real human prose, and detection goes away. Edit 2-3 characters (emdashes, lists, etc) and detection goes away.

And that's for just basic detection. There have been plenty of examples of 100% human written content (either old, or unpublished) that gets falsely flagged as AI.

And these are just technical aspects. The main issue is that pangram and other solutions are being used to summarily judge students work, and that is orders of magnitude more fucked up. Accusing someone of cheating can have devastating effects on their education/career/etc. and they're doing it with snake-oil closed boxes, at scale. We really really shouldn't support this, especially here on a technical site.