According to this page [1], they do use external sources (Google, Mojeek, Yandex and more), but not Bing ;)

They also have their (two) own indexes.

Tbh, for me (as small town dev) it feels like magic how fast those different sources are combined, additionally with user search preferences like raising or blocking certain domains. Insides welcome :)

Edit: Here [2] are some benchmarks and general strategies they pursue. Would love to read more details.

[1] https://help.kagi.com/kagi/search-details/search-sources.htm...

[2] https://help.kagi.com/kagi/search-details/search-speed.html