First-mention rate
First-mention rate is the share of sampled AI answers to a category prompt set in which a brand is the very first brand named. Being first in a spoken-style answer is worth more than being present, so this metric captures the part of AI visibility that visibility rate alone misses.
How to read it
A brand with a 60 percent visibility rate and a 10 percent first-mention rate is usually in the answer and rarely leads it. That pattern typically means the assistants know the brand but prefer a competitor, and the citations for those prompts show why.
Per engine
The engines disagree. It is common to lead first mentions on one engine and trail on another, because each retrieves from different sources. Read the metric per engine before reading the overall number.