They use a mixed index with a lot of different sources. (mentioned here)

They have direct licensing deals with Mojeek, Brave, Yandex, Wikipedia, TripAdvisor, Yelp, Apple, and Wolphram Alpha, which they claim is under "FRAND" ("Fair, Reasonable, And Non-Discriminatory") terms, with them retaining the ability to "reorder and blend results." (which is kinda their whole thing)

As for Google and Bing, they have to use third parties to get their search data, since:

Bing: Their terms didn’t work for us from the start. Microsoft’s terms prohibited reordering results or merging them with other sources - restrictions incompatible with Kagi’s approach. In February 2023, they announced price increases of up to 10x on some API tiers. Then in May 2025, they retired the Bing Search APIs entirely, effective August 2025, directing customers toward AI-focused alternatives like Azure AI Agents.

Google: Google does not offer a public search API. The only available path is an ad-syndication bundle with no changes to result presentation - the model Startpage uses. Ad syndication is a non-starter for Kagi’s ad-free subscription model.

They also run their own "Small Web Index", which prioritizes smaller sites, independently operated personal blogs, comic sites, small YT channels, things like that.

You can see some of that index on its own here. I don't often see it pop up for a lot of my searches, but I'd say maybe 1 in 20 to 1 in 50 of my searches have something that is clearly ranked from there higher in my search results, that I actually end up clicking on, that is almost always more reliable than all the other sources on the topic. It's usually most prevalent for programming/system setup related terms since there's a lot of programmers and sysadmins with their own personal blogs.

I've found they rank fediverse sites higher than Google, Bing, DuckDuckGo, and Ecosia do, though I don't know if that's just their general search ranking or if that's part of the smallweb index. Again, usually much more relevant and useful than other sites or even Reddit when they do appear.