Both major labs switched on text watermarking within 48 hours at the turn of August. My first thought was that this is very hard to do in a way that actually holds text has no pixel layer to hide anything in. So I read Anthropic's own documentation on how it works.
It does work. It also breaks in a lot of ordinary situations, and they say so themselves: short text leaves too little signal, heavy editing or translation thins it out, screenshots and format conversion strip it entirely.