What is query fan-out?
Query fan-out is a technique used by AI search systems in which a user question is broken into several related subqueries that are searched in parallel. The results of all subqueries feed into one combined answer. Google describes the technique for AI Overviews and AI Mode.
An example: for a question about the best accounting software for freelancers, a system may also search for pricing, for integrations with tax advisors, for reviews and for alternatives. The answer then rests on sources that match one of these subquestions, not only the original one.
It follows that a page can appear as a source in an answer even if it does not rank highly for the original query. Conversely, a good ranking for the main question is not enough if other pages answer the subquestions better.
Which subqueries a system generates is not directly visible from the outside. Some APIs return the searches they ran; consumer interfaces usually do not.
What it means for your website
For a website it pays to think through the obvious follow-up questions to a core question and answer them on their own: what it costs, how providers differ, what to know beforehand. A good test is to ask several variants of the customer question yourself and compare which sources get named each time. If the same third-party page shows up across variants, it points to a subquestion that page answers better than yours.
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