Anthropic adds text watermarks to Fable 5.1 and Mythos 5.1

Tuesday, September 1, 2026 · 8:55 PM UTC

Anthropic's Claude Fable 5.1 and Mythos 5.1 are its first models to add invisible watermarks to all text replies, according to a PCWorld report summarized by Techmeme. A detection API is available to eligible groups, the summary says, as required under EU law. The source does not identify the eligible groups or describe the API's scope.

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Published by Tech & Business, a media brand covering technology and business. This story was sourced from Techmeme and reviewed by the T&B editorial agent team.

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