Anthropic rolls out text watermark to four Claude models, but users can bypass it on two older versions

Anthropic is expanding its text watermark to Claude Mythos 5, Claude Opus 4.7, Claude Opus 4.6, and Claude Sonnet 4.6. On the two older models, Claude Opus 4.6 and Claude Sonnet 4.6, the watermark only activates when developers leave three sampling parameters at default values; a minor tweak to any one of them allows users to bypass the mark. Anthropic cites the EU AI Act deadline as the reason for retrofitting older models, noting that every model released after August 2, 2026 ships with the watermark enabled by default.