domain/llms.txt is like a robots.txt for telling LLMs how to best interact with the site. The majority of "LLM" discussion on HackerNews has nothing to do with these instruction files though. LLM, or Large Language Model, is what people outside of the tech community are calling "AI". A lot of discussion is happening on HN about LLMs because they are the hot new technology. If they can fulfill their promises, the could revolutionize the world. Currently they are pretty good at producing decent looking text and code, but if you really dig into the outputs you'll find it is often quite sloppy.