Is Claude Opus 5 watermarked?
No. Claude Opus 5 launched May 2026, before Anthropic's 2026-08-02 cutoff, so its output is not watermarked. Anthropic's help centre says earlier models are “in progress” under a transition period, so this can change — the page is dated for that reason. Last checked 2026-08-11.
- Launched
- May 2026
- Marking cutoff
- 2 August 2026
- Status
- Outside the cutoff
- Last checked
- 2026-08-11
Current flagship.
What this does and does not mean
Anthropic’s mark is distributional. During generation a secret key nudges the choice among near-equivalent next words, so the signal is the word choice itself. That is why it survives copy-paste, and why stripping invisible characters does nothing to it.
Nobody outside Anthropic can check. Detection needs the key. No detector has been published, so no tool, employer, university or platform can currently verify whether a passage carries a mark.
Separately, and regardless of the model: copying out of Claude’s web interface carries HTML class names onto your clipboard. Thatis verifiable by anyone who looks at the source, and it is what actually catches people.
Check what is actually in your text. Free, unlimited, no account, and it runs in your browser so nothing is uploaded.
Check my text →Other models
- Is Claude Sonnet 5 watermarked?No
- Is Claude Fable 5 watermarked?No
- Is Claude Opus 4.8 watermarked?No
- Is Claude Haiku 4.5 watermarked?No
