"Our data includes anonymized API calls to traditional search indexes like Google, Yandex, Mojeek and Brave, specialized search engines like Marginalia, and sources of vertical information like Wolfram Alpha, Apple, Wikipedia, Open Meteo, Yelp, TripAdvisor and other APIs. Typically every search query on Kagi will call a number of different sources at the same time, all with the purpose of bringing the best possible search results to the user."
Not to mention that they have their own index that they're constantly working to expand:
> But most importantly, we are known for our unique results, coming from our web index (internal name - Teclis) and news index (internal name - TinyGem). Kagi's indexes provide unique results that help you discover non-commercial websites and "small web" discussions surrounding a particular topic. Kagi's Teclis and TinyGem indexes are both available as an API.
The comment I replied to implied that they have their own large index equivalent to Google's and so don't need to use Google. It's not true, and I bet you would find that a very significant portion of the search results come directly from Google queries behind the scenes.
So that's only telling a small part of the story.