Apple sent developers a reminder on Wednesday that Mac apps need to support 64-bit by June 4. The company sent the following message outlining the details.
“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 also indicated that users of 32-bit apps will see the message pictured above when launching the app for the first time in macOS 10.13.4. For much more information on 32-bit and 64-bit apps and the upcoming transition, see Apple’s support document which can be found here: support.apple.com/en-us/HT208436