Apple has started preparing the deprecation of 32-bit apps for macOS. The next maintenance release of macOS, High Sierra 10.13.4, will notify users when they launch 32-bit apps, while the upcoming Xcode 9.3 will include tools to make the transition to 64-bit less painful for developers.
Following the WWDC 2017 announcement, Apple stopped accepting the submission of 32-bit apps for macOS on January 1 of this year, while updates to existing 32-bit apps will only be considered until June of this year. With next macOS release, Apple is going one step further by introducing an explicit alert for users. Indeed, according to macOS 10.13.4 release notes,
To prepare for a future release of macOS in which 32-bit software will no longer run without compromise, starting in macOS High Sierra 10.13.4, a user is notified on the launch of an app that depends on 32-bit software. The alert appears only once per app.
Apple’s strategy to deprecate 32-bit apps for macOS closely resembles what Apple did to deprecate 32-bit apps for iOS. Starting with iOS 10.3, indeed, iOS users were shown an alert each time they launched a 32-bit app. Support for 32-bit apps was finally removed in iOS 11.
This time, Apple is also providing extended support to developers through a set of new diagnostic tools in Xcode 9.3 to make the transition easier. In particular, developers can enable a new 64-bit test mode to make any attempt to run 32-bit code to either trigger an alert for apps or a silent failure for other types of software, including Dashboard and WebKit plugins. This test mode can be enabled by executing sudo nvram boot-args="-no32exec" in a Terminal and then restarting the machine. Once developers have ensured their apps work correctly in 64-bit-only mode, they can re-enable normal behaviour by executing sudo nvram boot-args="" and the restarting again the machine.
In future versions of macOS, the 64-bit test mode may provide additional information for the developer to help test and qualify software, says Apple.