Claude Introduces Invisible Watermarks: The End of AI Copy-Paste Cheating?

Anthropic now hides a watermark in every text that Claude writes. Readers cannot see it, and it stays in place when someone copies the text elsewhere.

New models carry the mark worldwide. Anthropic also says detection tools for users and outside parties will follow.

How the Claude Watermark Works

Anthropic applies the mark at the model level. Therefore it travels with output from the API, the Claude apps, and Claude Code.

Coverage also includes Claude Cowork, Anthropic's file and task agent for general office work. Claude Tag, which puts the model inside Slack, carries the mark too.

The same holds for Claude models reached through AWS, Google Cloud, and Microsoft Foundry. Region makes no difference either. Anthropic has not published its method. Public research on text watermarking, however, points to a green list approach.

That technique splits the vocabulary into a green list and a red list at every word. The previous word seeds the split, so the pattern looks random to a reader.

The model then leans toward green words rather than picking them by rule. A detector counts them and checks whether the share beats chance. The design explains the two gaps Anthropic flags. Short passages hold too few words for a reliable count. A paraphrase, meanwhile, swaps the green words out.

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