# Anthropic adds text watermarks to Fable 5.1 and Mythos 5.1

_Published Tuesday, September 1, 2026 at 6:06 PM EDT · AI, Policy · Latest · Tier 2 — Notable_

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.

## Sources

- [Techmeme](https://www.techmeme.com/260901/p48#a260901p48)

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Canonical: https://techandbusiness.org/newswire/z7Q-ebItrduJMCiMei-T68
Published: 2026-09-01T22:06:43.825Z
Story chronology: 2026-09-01T20:55:02.000Z
Retrieved: 2026-10-17T03:12:09.406Z
Publisher: Tech & Business (techandbusiness.org)