Models New
Anthropic extends its text watermark to four older Claude models, but on two of them it applies only at default sampling settings
Published:
In an email to API customers reported by The Decoder, Anthropic says it will watermark the text output of Claude Mythos 5, Claude Opus 4.7, Claude Opus 4.6 and Claude Sonnet 4.6. Newer models such as Claude Opus 5.5 already carry the mark, and the rollout on Amazon Bedrock may take a few extra days.
On Opus 4.6 and Sonnet 4.6, the email says, the watermark applies only when the three sampling parameters stay at their default values, so changing any one of them avoids it. The Decoder quotes the email: "If you rely on the watermark for your own compliance, keep these settings at their defaults."
Anthropic's help page says it has signed the EU AI Act's Article 50(2) Code of Practice on transparency of AI-generated content, that models launched in the EU on or after 2 August 2026 mark their output at launch, and that watermark detection is in private preview for eligible organisations such as regulators, researchers and the media.
Caveat. The email was not seen directly. The Decoder infers, because the email does not say otherwise, that Mythos 5 and Opus 4.7 are watermarked whatever the settings; that is not confirmed.
Sources