Do they? Their selling point is trustworthiness and privacy, not the software.

As most business's their internal code is probably a giant ball of mud that runs on caffeine and poor amounts of sleep. It works, but it probably wouldn't be reasonably releasable without refactoring and reworking a lot of the source so that it's componetized in some way.

Personally I just want DDG to make a search API that is free and doesn't require API keys. That way I can setup search in mobile or desktop apps and have it automagically be searching through specific sites like Soundcloud and Youtube and such.

Like if they're reading this, DDG is very unique and if they were to focus upon reducing costs, making efficient software, and better algorithms, DDG could be the service we shove into apps.

That won't happen as every API call to DDG would result in an API call to Bing/Yandex/Yahoo which they have to pay for.

Their selling point is trustworthiness, privacy and usefulness. To be useful, they must have quality software/IP. And in their opinion, that should be protected.

I much rather trust a product that is open source, which makes me slightly uncomfortable and concerned about DDG.

So let's say they release their source code - how can they possibly prove that their servers are running that same code?

If the code was AGPL'd and included contributions for which DDG didn't own the copyright (so DDG would be using the code under the terms of the AGPL), they'd be breaking the licence terms if they failed to disclose any changes.

It wouldn't be proof, but it would be a fairly strong commitment.

at least for some functionalities, you can run it on your computer and observe the same behavior

Will they protect my IP somehow?