Tomorrow at midnight PT, Apple will begin issuing an alert box when you open a 32-bit app in MacOS 10.13.4. It’s a one-time (per app) alert, designed to help MacOS make the full transition to 64-bit. At some unspecified time in the future, the operating system will end its support for 32-bit technology… meaning those apps that haven’t been updated just won’t work.
That time, mind you, is not tomorrow, but the company’s hoping that this messaging will help light a fire under users and developers to upgrade before that day comes.
I expect most Apple tech support people heard this news and just cringed thinking about all the support calls they are going to get over this news.