OpenAI, Google, Microsoft and Anthropic back one robots.txt AI training opt-out

TL;DR

• On 30 October OpenAI, Google and Microsoft said they'll support one shared robots.txt signal for AI training, and The Verge and The Next Web report Anthropic will too.
• A site would write one group for the token __usage_ai-training, without a separate training rule for each company's crawler.
• None of the four has it running yet, and the draft has no formal standing at the IETF.