Anthropic is extending its text watermark to four more Claude models: 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. According to an email Anthropic sent to API customers, the rollout on Amazon Bedrock may take a few extra days.
Anthropic describes the watermark as an "imperceptible pattern in word choice" that does not change meaning, quality, or readability. The company says it adds no extra characters or tokens, does not 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 conversations with Claude."
On Claude Opus 4.6 and Claude Sonnet 4.6, the email says the watermark applies only when developers leave the three sampling parameters at their default values. Those parameters are temperature, top_p, and top_k, which control how much randomness the model uses when choosing words. According to the email, a minor change to any one of them is enough to avoid the watermark. Anthropic warns: "If you rely on the watermark for your own compliance, keep these settings at their defaults." The email