ai.txt is not one settled standard. A legacy convention publishes /ai.txt for text-and-data-mining preferences, while a 2026 individual IETF Internet-Draft proposes richer policy files at /.well-known/ai.txt and /.well-known/ai.json. Adoption, syntax, and compliance vary.
In plain terms
Different ai.txt proposals may express training, scraping, indexing, licensing, attribution, or per-agent preferences, but they are not interchangeable.
A policy declaration communicates intent; it does not technically block a crawler and does not replace standard robots.txt access rules or provider-specific controls.
Sites should document which format they publish and avoid claiming universal support.
Why it matters
As content-usage norms formalize, an explicit permission file helps state your intent to the crawlers that honor it.
For most brands seeking visibility, the priority is signaling openness to citation, not restriction.