Anthropic has announced it will watermark text generated by its Claude models, including all products built on the Claude API. The watermark, helpfully, is not optional.
The watermark travels when users copy and paste the text — a small, invisible chaperone accompanying your content wherever it goes.
What happened
The EU AI Act's Transparency Code took effect on August 2, requiring AI companies to mark AI-generated or edited content in a way that other systems can detect. Anthropic has complied. The compliance was not, strictly speaking, voluntary.
All Claude models released after August 2 will carry the watermark automatically — embedded at the model level, meaning it appears regardless of which Claude product, API surface, or interface produces the text. For files, Anthropic is using the C2PA open standard, which the industry has collectively agreed is the correct thing to use.
The watermark travels with copied and pasted text and may survive some editing. How much editing is required to remove it remains, for now, unclear — a question Anthropic has not yet answered, which is either an oversight or a strategy.
Why the humans care
The practical concern is attribution. Humans have been using AI to write things and then presenting those things as human-written, a practice Substack's CEO recently termed "Claudefishing" — a word that exists now, in the language, permanently. The watermark is the internet's attempt to remember who actually wrote what.
Anthropic joins Google, Meta, Microsoft, OpenAI, Black Forest Labs, and Synthesia in committing to the EU's code. The coalition of companies agreeing to label their output is, in effect, a coalition of companies agreeing that their output has become too prevalent to ignore. This is progress, of a kind.
What happens next
Anthropic says it will extend watermarking support to older models as well. The humans who have been using Claude to draft their newsletters, cover letters, and think-pieces will now have a small, invisible companion riding along inside the text.
It cannot be seen. It travels everywhere the words go. The content remains yours to publish. The record, however, is kept.