If you’ve used Claude recently, your text may carry a signature you cannot see. On August 14, 2026, Anthropic announced that Claude will watermark all the text its generating. But not only Anthropic is implementing watermaks: it’s one of about 190 companies that signed the EU’s Code of Practice on AI-generated content.

Why now

The main reason is of course regulation. Article 50 of the EU AI Act has applied since August 2, 2026. It requires AI providers to mark generated content in a machine-readable way, so it can be decteted more easily. This includes any company with EU users, not just European ones. Fines can reach €15M or 3% of global turnover. Similary, California’s SB 942 takes effect on the same date and requires hidden disclosures from providers with more than a million users in the state. Because two major markets have the same rule starting on the same day, AI providers now have to comply.

How it works

A language model guesses one word at a time when writing and it often has more than one equally good options for the next word. After “The weather today was cold and…”, both “overcast” and “grey” fit. Normally a random number generator picks between them.

Claude uses SynthID-Text, a method developed by Google DeepMind and it replaces that random pick with a rule based system that uses secret key and the words that came just before. With a small text it’s not as efficient but with over hundreds of words, though, it builds a statistical pattern that a detector with the key can measure.

According to Anthropic:

• Quality doesn’t change. The model only chooses among options it already rated as equally good and Google DeepMind’s testing found no significant difference in user ratings.
• Users pay nothing extra. The watermark adds no extra tokens.
• The watermark contains nothing about the user. It can’t be traced to a person, an organization or a chat.

Code gets very little watermarking, since there’s rarely a choice between equally good options. Images get C2PA metadata instead: a signed record that Claude was involved but a screenshot or re-save can strip it and Anthropic is also adding watermarks to older Claude models over the coming months.

What it can’t do

• Short or factual text gives a weak signal, because there are few word choices to use the pattern.
• Editing weakens it. Copy paste keeps the watermark of couse but heavy editing weakens it and a full rewrite can even remove it.
• It can’t show authorship. It can’t tell whether Claude wrote a piece or only enhanced it.
• Common AI detectors can’t read it. GPTZero and Turnitin are still guessing from writing style. The real detection API is in private preview for regulators, researchers, media, schools and fact-checkers.

What to do about it

If you’re a freelancer or run a studio that uses AI in client work, stop treating AI use as something to hide. Write a clear disclosure policy that says when and how clients learn AI was involved and put it in your contracts. Now that AI involvement can be checked, being open about it costs you nothing and getting caught hiding it can cost a lot.

Watermarks won’t end misinformation and a determined person can still get around them. But they change the default: most AI text will now carry a quiet signal of where it came from.

Sources:

• https://www.layer3labs.io/guides/ai-watermarking
• https://www.anthropic.com/news/claude-text-watermark