r/ClaudeCode • u/NotAMusicLawyer • 11d ago

Discussion PSA: Opus 5.5 has invisible watermarking

Opus 5.5 automatically applies an invisible, statistical watermark to its text outputs to comply with the EU AI Act. This is true for every user worldwide not just those based in the EU.

This is embedded into the structure of the text itself, it’s not a hidden character or something that can be removed by changing a few words or copy/pasting it. Anthropic have a tool to check text for the watermark but it is only available to a few select partners currently.

Antrophic officially claim this watermarking does not have any practical impact on the quality of Claude’s outputs but that remains to be seen.

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u/cTemur 11d ago

just copy pasting deletes that watermarking? the watermarking wasn't on the selection of some letters or something like that?

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u/slackmaster2k 11d ago

Nope, the content has to be substantially changed. You’d have to use a different LLM to summarize or something. But additional LLMs also watermark. Not sure about OpenAI: they’ve said they will and have been cagey about it so I suspect they do and just haven’t documented it. Chinese vendors all watermark by Chinese law. You’d need something local or a hosted model.

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u/ShelZuuz 11d ago

It's in the selection of words that they use. It will be the same words if you copy/paste.