Claude Opus 5.5 carries the text watermark, Anthropic's table shows

Published 26 September 2026

Anthropic's help article now lists Claude Opus 5.5 as carrying all three of its marks: the text watermark on Anthropic's own surfaces, the text watermark through AWS, Google Cloud and Microsoft Foundry, and C2PA Content Credentials on files. That makes four models with the text watermark: Claude Fable 5.1, Mythos 5.1, Opus 5.5 and Opus 5[1].

What changed

The table headed "Which Claude models support watermarking" gained one row. The archived copy of the article from 21 September 2026 does not have it; the page as read on 26 September 2026 does. Nothing else in the article body changed. Opus 5.5 carries no footnote, where Opus 5 still has one saying its cloud-partner rollout began on 14 September 2026 and would be complete within a week[1]. The table now lists fourteen models for Content Credentials, and the other ten remain listed for files only[1]. Anthropic's developer documentation also added Opus 5.5 to the models that support the code execution tool, which is where the API signs generated files[13].

What it means

Text from Opus 5.5 is listed as marked both on Anthropic's own surfaces and through the cloud partners, and marking applies wherever Claude is offered, worldwide[1]. An unmarked response still says little on its own: it may come from a model listed for files only, and Anthropic says models released before 2 August 2026 will all be covered by 2 December 2026[1]. What Anthropic marks, and how.

What is still not known

The article does not say when the row was added, and Anthropic has not published detection accuracy for any model. The detector is still in private preview for organisations obliged to check under EU law[1]. What to do if a detector flags your text.

Last verified against primary sources: 2026-09-26