The unmarkable watermark

Article 50 of the EU AI Act takes effect on 2 August 2026, and generative-AI systems already on the market get four extra months — until 2 December — to comply. The rule is broad: any provider putting a system on the EU market must mark synthetic audio, images, video and text so the output is machine-readable and detectable as artificially generated, to a standard the law calls "effective, interoperable, robust and reliable." Breach it and the fine runs up to 15 million euros or 3% of worldwide turnover, whichever is larger.

no single active marking technique suffices — the EU's draft Code of Practice on marking AI-generated content

The catch is that text watermarking that survives paraphrasing, in the sense the law demands, does not exist. Google DeepMind's SynthID-Text is the leading technique; in the peer-reviewed literature its detection collapses when the text is simply passed through a paraphraser, with the writing barely changed — in one evaluation the scrub succeeded more than nine times in ten. Academic teams have removed LLM watermarks cheaply and at scale. A legally mandated marker of AI authorship can be erased by pasting a paragraph through a second model.

The EU's own draft Code of Practice effectively concedes the point: no single active-marking technique meets the bar, so it asks providers to stack a watermark on top of embedded metadata on top of server-side logging — defence in depth for a mark that can be individually defeated. Text is the hardest modality of the four, and the Code already carves out passages under a fixed character threshold from the imperceptible-watermark requirement entirely.

The reach is wide. Article 50 lands on essentially every business generating text, image, audio or video for EU users, and because the Act applies extraterritorially it binds OpenAI, Google, Anthropic, Meta and Mistral wherever they sit. The deadline is real and enforceable; the question the law leaves open is what compliance even means when the state of the art cannot deliver the tamper-resistance the statute names.