Passing off ChatGPT’s work as your own is about to get tougher—at least if you live in the European Union. On Monday, OpenAI announced that it would start inserting an invisible watermark, imperceptible to the naked eye but identifiable by machine, into all text outputs generated by its AI models, including ChatGPT and its coding agent Codex. The watermark will move OpenAI into compliance with the EU AI Act, which requires model-made text to include a mach