Apple's famous announcement is at https://developer.apple.com/news/?id=10202014a
64-bit and iOS 8 Requirements for New Apps
October 20, 2014 Starting February 1, 2015, new iOS apps uploaded to the App Store must include 64-bit support and be built with the iOS 8 SDK, included in Xcode 6 or later. To enable 64-bit in your project, we recommend using the default Xcode build setting of “Standard architectures” to build a single binary with both 32-bit and 64-bit code.
As discussed at What's the meaning of Base SDK, iOS deployment target, Target, and Project in xcode there is a difference between the "Base SDK" and the "Deployment Target" SDK.
May it please be explained to me whether Apple's announcement requiring "be built with the iOS8 SDK" refers to the former or the latter? Also, what explicit action, if any, is required by me to be compliant.