Starting with macOS High Sierra 10.13.4, Apple is commencing with its plan to begin phasing out 32-bit apps on Macs. Apple has promised that macOS High Sierra will be the "last macOS release to support 32-bit apps without compromises."
After installing macOS High Sierra 10.13.4, which is now available in a beta testing capacity, when you open up an app that's a 32-bit app, you'll get a warning about its future incompatibility with the macOS operating system.
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This is the first of many warnings Apple plans to provide as it works to put an end to 32-bit Mac apps, and this initial warning will only be shown one time for each app.
Apple's efforts to phase out 32-bit apps on Macs mirror the path it took when ending 32-bit app support on iOS devices. In iOS 10, Apple provided increasingly more insistent warnings to let users know that their apps wouldn't work with future versions of iOS before phasing out 32-bit support entirely in iOS 11.
As of January 2018, all new apps submitted to the Mac App Store must be 64-bit, and all apps and app updates submitted must be 64-bit by June of 2018. The next version of macOS after High Sierra will include "aggressive" warnings about 32-bit apps before they are phased out entirely.
Once 32-bit apps are phased out on Macs, they won't be able to be used at all, so users will need to find replacements for older 32-bit apps that aren't likely to be updated to 64-bit.
Top Rated Comments
32-bit support isn't free either. You need to test against your 32-bit libraries and if you update a 64-bit library for a security reason, you'll also need to update and test the corresponding 32-bit library. And it may behave differently.
Nvidia has stopped supporting 32-bit systems because the testing burden just got too big. A lot of Linux distros are killing 32-bit variants as well.
It's not worth the effort anymore.
Edited slightly to fix a typo and improve readability
The CPU has NO PROBLEM executing 32-bit code, and there isn't even a performance hit in doing so. There's no real solid reason to discontinue 32-bit support. This is going to keep people who requires certain older apps from upgrading to the latest version of MacOS, and expose them to security vulnerabilities for no good reason at all.
Apple have always been happy to drop older standards. 32 bit is only the latest in a long list. They did this in iOS and they’ve already dropped 32 bit support/plug-ins years ago for their Pro Apps (LPX), so this shouldn’t come as much surprise.
;-) Ok, ok, yeah. I get it. 32-bit overhead, memory, libraries, etc. But, but, I can't live without Adobe Fireworks ;-)