Now we know.
DuckDuckGo will continue to get results, and a few extra features like date filtering on results, from Yahoo by way of a custom integrations between each service. Here’s the text over on the Yahoo subdomain duckduckgo-owned-server.yahoo.net:
This DuckDuckGo owned server is operating on a subdomain (duckduckgo-owned-server.yahoo.net) that has been delegated to DuckDuckGo via DNS by Yahoo so that we can continue to protect your privacy. In accordance with our privacy policy, we never share any personal information with any of our partners, including Yahoo. To make that crystal clear, Yahoo itself published a privacy statement to that effect. For more information, you can read about our partnership with Yahoo and its technical implementation.
Essentially, DuckDuckGo gets to control the core components of the integration, which should allow them maintain their previous privacy commitments. I’m not sure if DuckDuckGo is the only service to get a deal like this, but their 335 million search queries last month probably didn’t hurt negotiations. If you read between the lines, Yahoo needed this more than DuckDuckGo did.