Developers, take note: apps submitted to the Mac App Store must be 64-bit by June 1

Developers, take note: beginning, all new app updates submitted to the Mac App Store must support 64-bit starting June 1. 

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.