Per https://duckduckgo.com/duckduckgo-help-pages/results/sources/:

We also maintain our own crawler (DuckDuckBot) and many indexes to support our results. Of course, we have more traditional links and images in our search results too, which we largely source from Bing. Our focus is synthesizing all these sources to create a superior search experience.

Broke yesterday for me, are you by-chance a moderator on Reddit? Apparently you can continue to use Boost if you are