64-bit Requirement for Mac Apps
As a reminder, new apps submitted to the Mac App Store must support 64-bit starting January 2018, and Mac app updates and existing apps must support 64-bit starting June 2018. 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. The last macOS release to support 32-bit apps without compromise is macOS High Sierra.
Learn more about distributing Mac apps.