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Both just give me a recaptcha. Start page doesn't:

Which search engines does it use? I couldn't find info, and I'm just curious.

Can't find full list either, but it at least includes Bing and Google: https://support.startpage.com/hc/en-us/articles/452243553384...

How do they send the query on your behalf privately, without incurring insane search api costs?