In June, Apple will require all Mac App Store apps to support 64-bit. Yesterday, the company informed developers macOS High Sierra 10.13.4 now warns users when opening 32-bit apps for the first time, of the impending change:
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.
As a reminder, new apps submitted to the Mac App Store must support 64-bit, and starting June 2018, app updates and existing apps must support 64-bit. If you distribute your apps outside the Mac App Store, we highly recommend distributing 64-bit binaries to make sure your users can continue to run your apps on future versions of macOS.
Apple noted the change back in December for developers, and noted at the time new apps submitted as of January 2018 would require 64-bit support.
Apple will hold WWDC 2018 from June 4-8 in San Jose. Should we expect some Mac announcements at this event, like last year?