Is Claude Sonnet 5 watermarked?
Not watermarked
No. Claude Sonnet 5 launched 30 June 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 2026-09-02.
Primary sources: Anthropic marking status · watermark mechanism and limitations
- Launched
- 30 June 2026
- Marking cutoff
- 2 August 2026
- Status
- Outside the cutoff
- Last checked
- 2026-09-02
What this means
This model predates Anthropic’s marking cutoff. Its text can still contain copy-paste HTML, invisible Unicode and stylistic tells, but those artifacts are not Anthropic’s statistical watermark.
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 Fable 5.1 watermarked?Yes
- Is Claude Mythos 5.1 watermarked?Yes
- Is Claude Opus 5 watermarked?No
- Is Claude Fable 5 watermarked?No
- Is Claude Mythos 5 watermarked?No
- Is Claude Opus 4.8 watermarked?No
- Is Claude Haiku 4.5 watermarked?No
