Apple has reminded developers that, beginning June 1, all new app updates submitted to the Mac App Store must support 64-bit.
Also, app updates and existing apps must support 64-bit. Apple tells developers that if they distribute your apps outside the Mac App Store, it’s “highly recommended” they distribute 64-bit binaries to make sure users can continue to run your apps on future versions of macOS.
With the recent release of macOS High Sierra 10.13.4, the first time users launch an app that does not support 64-bit they will see an alert that the app is not optimized for their Mac.
