Sure, they're completely transparent about it. You can find the proportion of external search results right under the filters, with further information in their FAQ. They integrate their own indexers but I believe bulk of the results come from Google, Bing & others (hence the relatively high per-query cost).

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

I meant that they were "completely reliant" on these APIs in terms of utility, not that 100% of search results are external. I'd love to be proven wrong on this but my impression is that without Google, Bing, and other APIs Kagi wouldn't be a functional and competitive product.

Thanks! Hopefully with all the (monetary and word of mouth) support they are getting, they can move in the direction of becoming completely independent.