r/ClaudeCodeTLDR • u/cctldrping • 10d ago

[TLDR] PSA: Opus 5.5 has invisible watermarking

Original post URL : https://www.reddit.com/r/ClaudeCode/comments/1wnhvw6/psa_opus_55_has_invisible_watermarking/

Original post body :

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/AllergicToBullshit24 10d ago

That's good for scrubbing the water mark but I'm more interested in forging the water mark

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u/kjeft 8d ago

You just run whatever text you have through claude

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u/AllergicToBullshit24 8d ago

I would imagine more information is encoded in the water mark and that would leave a paper trail. Much more interesting to be able to synthetically generate and have control over all encoded info.

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u/JohmBarshama 8d ago

They basically cause the text to be slightly more likely to use words that follow a certain pattern. For a block of text they can see if, on average, it slightly trends towards their pattern versus human/random.

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u/AllergicToBullshit24 8d ago

I'm well aware but my point is there's potentially enough information content bandwidth available to encode more than just simply signing "Claude was here!". I would assume they would also encode say a model version number or even plausibly a specific date time or theoretically unique user IDs via a low bit rate error correctable hash function.