Text from Claude Mythos 5, Opus 4.7 and Sonnet 4.6 now carries Anthropic's watermark; on Sonnet 4.6, non-default sampling settings may drop it
The watermark is live on three models on the listed platforms; requests and responses don't change, but teams that rely on it need to check their sampling parameters.
// Key points
- From November 3, text generated by Claude Mythos 5, Claude Opus 4.7 and Claude Sonnet 4.6 carries Anthropic's text watermark on the platforms listed in Anthropic's help article on how Claude marks AI-generated content
- On Sonnet 4.6, text from a request that sets temperature, top_p or top_k to a non-default value might not carry it; if you rely on the watermark, Anthropic says to omit all three, including values a framework or client library sets for you
- The linked documentation says the watermark adds no tokens or hidden characters, does not change meaning, quality or readability, and carries no information about the user or organization
Builder's takeNo code changes needed, but two checks. If a feature promises to disclose or detect AI-written text, confirm which models and platforms are covered instead of assuming all Claude output is marked. And if you pass sampling parameters to Sonnet 4.6 out of habit, decide whether you actually want them. In something like AI Interview, where people will ask whether an answer was AI-written, a watermark that depends on the model and the settings is a signal, not proof.
// Background · from #Anthropic
Full timeline →- Nov 4 Claude's Messages API adds message threads in beta: later turns send only the new messages, and a thread expires 5 minutes after its last request
- Nov 2 Microsoft dissects the tampered Claude Code extension served by Cursor's marketplace: versions 2.1.312 and 2.1.313 planted an SSH key, a reverse tunnel and persistence
- Nov 1 Claude Code 2.1.316 retires fast mode on Opus 4.8 on November 30, adds pooled group budgets to its gateway and a separate effort setting for subagents