Looks like they do. From their FAQ[3]:

> Our searching includes anonymized requests to traditional search indexes like Google and Bing as well as vertical sources like Wikipedia and DeepL or other APIs. We also have our own non-commercial index (Teclis), news index (TinyGem), and an AI for instant answers.

[3] https://kagi.com/faq#Where-are-your-results-coming-from

They use bing and google APIs (that’s where the cost mainly comes from as every querye requests from both), their own search index, and smaller indexes.

This is the most important question. Are you piggybacking off of existing search providers, or is this a search engine from the ground up?