I believe them. I had Gemini-3.1 Pro do essentially this seven months ago - specifically a loop of writing "Bye! Done!" repeatedly until manually stopped. Presumably some sort of pathological behaviour where it wasn't ranking the stop token highly when it should have been... but damned if I know why... it was an innocent prompt (and it had done the thing I asked it to before failing to stop).

huh fair. Still very surprising. I have a _very_ unfavourable view of Google models, so I can kinda believe 3.1 pro could loop.

Still would never have predicted this. Even 2.5-flash was pretty good. Never saw anything like this happen.