Claude’s hidden watermark: Anthropic explains AI-written text tagging

Anthropic detailed Claude’s text watermarking system, based on the SynthID-Text approach, which uses low-stakes word choices to imprint an undetectable pattern that signals AI involvement without affecting output, extra tokens, or reader experience; a forthcoming detection API will let users check text, but the watermark is not a foolproof test for human vs. AI authorship and works best on longer passages, with reduced effectiveness on factual or short samples.