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Anthropic has begun embedding invisible, machine-readable watermarks into text generated by its Claude AI models, in a move driven by EU AI Act transparency rules that the company has chosen to apply globally.
The watermarking began on August 2, 2026, responding to transparency requirements under Article 50 of the EU AI Act. Anthropic says those markings will apply worldwide, not only to users in Europe.
Because the watermark is part of the text, it will travel with the text when it is copied and pasted elsewhere, and may persist through some editing. Watermarking is applied at the model level, meaning it is present no matter which Claude product or surface the text comes from.
Claude markings cover output from supported models everywhere Claude is used, including Claude Platform (API), Claude Code, Claude Cowork, and Claude Tag. Embedded watermarks will also apply when supported Claude models are accessed through AWS, Google Cloud and Microsoft Foundry, although signed provenance metadata may not be available on every platform.
For image and file outputs, the approach differs. When Claude generates a supported file type, such as a .svg, .png, or .jpg, it will attach signed provenance metadata following the Coalition for Content Provenance and Authenticity (C2PA) open standard. If a signed metadata label is present, it signals that a file was processed by Claude and lets users detect whether the file has been tampered with.
The system carries a critical limitation for anyone relying on it to prove authorship. The mark signals that Claude processed the text, not that Claude authored it. A person who asks Claude to proofread, translate or reformat their work will receive back a Claude-marked document. The mark does not distinguish between Claude having generated the content and Claude having lightly corrected punctuation.
Conversely, the absence of a watermark does not prove that content was written without AI. Marks may not be detectable if content was generated by an older model, heavily edited, paraphrased, translated or mixed with other writing. Very short passages may also not contain enough text for a reliable signal.
Legacy Claude models released before August 2, 2026, are covered by a transition period, with Anthropic working to add watermarking support to pre-August models before December 2, 2026. Anthropic said it is working on tools that will allow users and third parties to detect Claude's embedded watermarks and provenance metadata.
