How AI Watermarking Actually Works at the Token Level — And Why Developers Should Pay Attention
On August 11, 2026, Anthropic confirmed that Claude would start embedding machine-readable watermarks into the text it generates. The change wasn't optional. Article 50 of the EU AI Act, which requires providers of systems that generate synthetic text, image, audio, or video content to make those outputs machine-detectable as AI-generated, had already taken effect nine days earlier, on August 2.
Most people hear "watermark" and think of something like a logo stamped in the corner of an image, or a hidden tag buried in a file's metadata. Text watermarking doesn't work that way. It operates at the token level, inside the model, during word selection itself. Nothing is added to the text. There are no hidden characters. It's invisible to readers and undetectable without a matching cryptographic key — but statistically present all the same.
By the end of this article, you'll understand how that works, which providers have...
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