How Claude marks AI-generated content
Primary source: Anthropic Help Center (EU AI Act Article 50(2) Code of Practice).
Policy snapshot
| Topic | Anthropic position |
|---|---|
| New models | Marking for models launched on/after 2026-08-02 |
| Older models | Transition; “in progress” |
| Surfaces | API, Claude, Claude Code, Cowork, Tag |
| Regions | Worldwide |
| Detection | Third-party detection promised; docs forthcoming |
Mechanism 1 — embedded text watermarks
- Applied at the model level into the text itself (not file metadata).
- Imperceptible; survives copy-paste; may survive light editing.
- Weakened by paraphrase, translation, heavy edit, mixing, short text.
Likely technical class (Anthropic has not published the algorithm): statistical token-sampling watermarks (Kirchenbauer / SynthID-style). See vendor-notes.md and mark-classes.md.
Layer A scripts only remove Unicode / homoglyph carriers. Layer B (rewrite) targets statistical marks.
Mechanism 2 — C2PA on files
- Signed Content Credentials on supported types (examples:
.png,.jpg,.svg). - Tamper-evident while present; stripped by re-encode, metadata scrub, or many upload pipelines.
- Inspect with
c2patoolwhen installed; strip viaclean_image.py/clean_file.py/ ExifTool.
Caveats (Anthropic)
- Detected mark ⇒ content may have been processed by Claude — not proof of sole authorship.
- No mark ≠ human-only origin.
- Proofreading / translate / summarize can stamp human material.