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OpenAI starts watermarking ChatGPT and Codex text in the EU to meet AI Act rules

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OpenAI said it will add an invisible statistical watermark (textGrain) to eligible ChatGPT and Codex text for users in the European Union over the coming weeks, to meet the AI Act's requirement that generated content be machine-detectable. API customers anywhere can opt in, with watermarking off by default. Access to the detector opens first to approved researchers and expert organisations, case by case, because of the risk of false positives.

Why it matters

It is one of the first concrete large-scale answers to the EU's AI-content marking duties, and shows the limits: short or heavily edited text is hard to detect, and the detector is not public.

SourceOpenAI: Our approach to EU text provenance rules Checked against the primary source. Independently fact-checked on 7 Oct 2026.
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