Anthropic rolled out a new text watermarking system for Claude models that uses statistical sampling, not hidden characters. The company published details on August 14, 2026, confirming it's active on models released after August 2, 2026.
The system meets EU AI Act Article 50 transparency requirements and is on globally. Claude's watermark adds nothing to the text; it changes how the model samples the next word.
Removing the watermark requires an independent system to reconstruct the draft with the same meaning, resampling every word. Light edits or Unicode cleaners fail because no physical characters are present.
Statistical watermarks need sufficient sample size for reliable detection; very short outputs, typically under 100–200 words, lack the necessary mathematical density.