MacOS also finishes 32-bit version compliance following iOS, and "High Sierra 10.13.4" or later displays a notification when the 32-bit version application starts up

Apple announced in the release notes for macOS High Sierra 10.13.4 Beta that 32-bit software will no longer work on future macOS. Although it will not stop immediate from updating, 10.13.4 or later will notify the user when launching applications that rely on 32-bit software.

Apple Seeds First Beta of MacOS High Sierra 10.13.4 to Developers - Mac Rumors
https://www.macrumors.com/2018/01/24/apple-seeds-first-beta-of-macos-high-sierra-10-13-4/


Apple prepares macOS users for discontinuation of 32-bit app support | Ars Technica
https://arstechnica.com/gadgets/2018/01/apple-prepares-macos-users-for-discontinuation-of-32-bit-app-support/

For iOS applications64-bit version support is essential from February 2015It was released in the fall of 2017iOS 11We finished correspondence with 32 bit version.

Applications for macOS were not required to support 64 bit yet, but in Apple's June 20, 2017 WWDC 2017 "Since the January 2018 application for macOS delivered on the Mac App Store 64-bit compatibility is essential" And announce.

64-bit Requirement for Mac Apps - News - Apple Developer
https://developer.apple.com/news/?id=06282017a


And with macOS High Sierra 10.13.4 Beta version, it became clear that 32 bit version correspondence will close soon.

Although it is not clearly specified when the time to finish the correspondence of the 32 bit version concretely, if you apply the previous example of iOS as it is, it is thought that support will be terminated around 2020.