Apple developers should start transitioning their applications to support 64-bit. With the release of macOS High Sierra 10.13.4, Apple will start warning users if they launch an app that doesn’t have 64-bit support. All new apps submitted to the Mac App Store must have 64-bit support, and all app updates and existing apps must support this by June 2018. Apple says 64-bit apps can dramatically improve the memory and performance of a system. All modern Macs include powerful 64-bit processors, and macOS runs advanced 64-bit apps,” the company wrote.