Google, Microsoft, OpenAI and Anthropic back one shared AI training opt-out for websites

The four companies said they will honor a single robots.txt policy token, __usage_ai-training, that lets a site keep its content out of generative AI training without writing separate rules for each crawler. The token comes from an individual IETF draft submitted by Anthropic and states a usage preference rather than blocking crawling. Anthropic has begun implementing it, Microsoft will honor it from February 1, 2027, Google plans support in early 2027 and will treat it as a Google-Extended block, and OpenAI says it will follow in the coming months. Microsoft is also adding page-level training controls and a separate AI grounding preference.