Anthropic's text watermark is easy to bypass on several older Claude models - The Decoder
By Google News AI ·
Anthropic emailed API customers again about a second round of watermark retrofits. Starting November 16, 2026, Claude Opus 4.6, Claude Opus 4.5, Claude Sonnet 4.5, and Claude Haiku 4.5 will all get text watermarking. On Amazon Bedrock, the rollout may take a few extra days.
Claude Opus 4.6 was originally part of the first wave and should have gotten the watermark on November 3. Anthropic explicitly confirms the delay to November 16 but gives no reason. The other three first-wave models, Claude Mythos 5, Claude Opus 4.7, and Claude Sonnet 4.6, don't show up in the new email so their rollout likely went ahead on November 3 as planned.
Claude Opus 4.5, Claude Sonnet 4.5, and Claude Haiku 4.5 are three models that weren't part of the previous announcement. All four models in this wave share the same sampling restriction: the watermark only applies when temperature, top_p, and top_k are set to their defaults. In the first wave, that limit only hit two of four models (Opus 4.6 and Sonnet 4.6).
Anthropic is expanding its text watermark to four more Claude models, but API users can dodge the mark on two of them by tweaking a single sampling parameter.
In an email to API customers, Anthropic said it will watermark Claude Mythos 5, Claude Opus 4.7, Claude Opus 4.6, and Claude Sonnet 4.6. Newer models like Claude Opus 5.5 already carry the mark, and the rollout on Amazon Bedrock may take a few extra days.
Anthropic calls the watermark an "imperceptible pattern in word choice" that doesn't change meaning, quality, or readability. The company says it adds no extra characters or tokens, doesn't affect pricing or request and response formats, and barely slows output speed. Anthropic also says the watermark "contains no information about the user, their organization, or their…
Originally published by Google News AI
