Apple made an announcement for developers recently:
64-bit and iOS 8 Requirements for New Apps
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.
This means that both FileMaker with FileMaker Go and Xojo with their iOS support have to build apps with 32 and 64 bit support as universal apps. Those apps will than use the native architecture of the phone they run on. This avoids the need to load 32bit libraries on a 64bit Phone and saves memory. Currently FileMaker Go 13 ships with code for armv7 and armv7s, but all 32-bit.