Short answer: Yes. OpenAI said on October 5, 2026 that over the coming weeks it will add an invisible watermark to eligible ChatGPT and Codex text output in the European Union, to meet the EU AI Act’s requirement that AI-generated text be identifiable by machines.
The watermark, called textGrain, is not a visible symbol; it adds a hidden statistical pattern to the model’s word choices that a detector can recognize. Outside the EU it is not on by default, though API customers worldwide can opt in for select models. OpenAI says the signal can be weakened by editing (swapping 10% of words for synonyms cut detection from about 92% to 66%), and detector access is initially limited to approved researchers and expert organizations.
Source: OpenAI: Our approach to EU text provenance rules
Image: Flag of Europe, public domain, via Wikimedia Commons.