Is Claude Mythos 5 watermarked?
Not watermarked
No. Claude Mythos 5 launched 9 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
- 9 June 2026
- Marking cutoff
- 2 August 2026
- Status
- Outside the cutoff
- Last checked
- 2026-09-02
Limited availability through Project Glasswing. No self-serve access.
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 Sonnet 5 watermarked?No
- Is Claude Fable 5 watermarked?No
- Is Claude Opus 4.8 watermarked?No
- Is Claude Haiku 4.5 watermarked?No
