How does GEO (SEO for AI) work?

This is my blog, trying to articulate and improve my understanding in the age of Gen ai.

What I don't understand is how can companies like Profound measure the real value of brand mentions in AI responses. Isn't the chat access only with the AI companies?

PS: In this blog I have mentioned that llms.txt is an index analogous to robots.txt. This is incorrect and I would change it.