Previewed at WWDC, launching in the fall.
Apple Releases macOS High Sierra 10.13.5 With Messages in iCloud Support
macOS High Sierra 10.13.5 can be downloaded directly from the Mac App Store or through the Software Update function in the Mac App Store on all compatible Macs that are already running macOS High Sierra.
The macOS High Sierra 10.13.5 update introduces support for Messages in iCloud, a feature that Apple has been testing and working on since macOS High Sierra was announced last June.
Messages in iCloud, as the name suggests, stores your iMessages in iCloud rather than on each of your individual devices, introducing improved cross-device syncing and saving on-device storage space. Messages in iCloud support is also available in iOS 11.4, which was released to the public earlier this week.
macOS High Sierra will be followed by macOS 10.14, a next-generation version of macOS that Apple is expected to introduce at the Worldwide Developers Conference next week.