Which Claude models are watermarked? (live list)
By Claude Watermark Research · Updated
No Claude model you can currently select carries Anthropic's text watermark. The policy applies to models launched on or after 2 August 2026, and every shipped model — Opus 5, Sonnet 5, Fable 5, Opus 4.8 and Haiku 4.5 — launched before that date. The announcement is real and the cutoff is real; the marked models have simply not arrived yet.
The rule is a launch date, not a model family
Anthropic's condition is about when a model launched, not what it is called or how capable it is. Any model that launches on or after 2 August 2026 is in scope. Anything that shipped before is not, unless Anthropic retrofits it — which it has said it is working towards but has not done.
This is why the question “is Opus watermarked?” has no stable answer. It depends entirely on which Opus, and on a date. A future Opus release would be marked; the one you are using today is not.
Why people believe their text is already marked
The announcement was widely covered, and coverage rarely mentioned the cutoff. If you read only the headline, the reasonable conclusion is that Claude output became watermarked in August 2026. It did not — the policy did.
The confusion is compounded by a real artifact that does exist today: copying from the Claude web interface carries HTML class names such as `font-claude-response-body` into whatever you paste into. That is genuinely detectable, it is what the AO3 skin catches, and it has nothing to do with the statistical watermark.
What changes when a marked model ships
The mark is distributional: a secret key biases the choice among near-equivalent next tokens, leaving a statistical signature spread across the passage. It survives copy-paste because the signal is the word choice itself.
Detection requires the key, so only Anthropic can check. There is no published detector, which means nobody outside Anthropic can confirm a passage is marked — and by the same token, nobody can confirm a removal worked. Any tool claiming to verify either is claiming something it cannot do.
Questions
- Is Claude Opus 5 watermarked?
- No. Opus 5 launched before 2 August 2026, so it falls outside the policy. The same applies to Sonnet 5, Fable 5, Opus 4.8 and Haiku 4.5.
- Will older models be watermarked retroactively?
- Anthropic has said it is working to extend marking to earlier models. Until that ships, output from those models carries no statistical mark.
- Does the API differ from claude.ai?
- No. The policy is model-based and applies across claude.ai, the API, Claude Code and the other surfaces. There is no paid tier that disables it.
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