A watermark in plain text sounds impossible. Text has no pixels to hide data in, and no metadata survives copy-and-paste; every character is right there in front of you. Where could a mark possibly go?
And yet the marks are real. Google has watermarked text from the Gemini app and web experience since 2024 (its API is, at the time of writing, a documented exception), and as of August 2026, new Claude models mark text at the model level, with earlier models to follow. They're invisible, they survive copying, and they work because they don't live in the characters at all. They live in the choices between words.
The one idea in this step: a model writes by rolling weighted dice between several words that would each be fine.
When a model is mid-sentence, it doesn't know "the next word." It has a shortlist, like autocomplete, with preferences. Here's a real kind of moment, one word from the end of a sentence:
