OpenAI Adds Invisible Watermarks to ChatGPT in the EU

OpenAI said Oct. 5, 2026 it will add an invisible watermark to ChatGPT and Codex output in the EU to meet the EU AI Act. The system subtly steers word choice in a way that survives copy-paste. It rolls out over coming weeks. API developers worldwide can opt in, but it will not be on by default globally.