This week Apple released iOS 11.4 and watchOS 4.3.1 + tvOS 11.4, but it still lacked the macOS High Sierra 10.13.5. In addition: its final build (17F77) is now officially available to all users.
His biggest news, certainly, is the arrival of Messages on iCloud. With this, all your conversation history through the Messages application (Messages) is synchronized in the cloud via iCloud. So, regardless of how many Apple devices you have, when receiving or deleting a message on one, the same behavior extends to the others.
Here's the changelog official:
The update for macOS High Sierra 10.13.5 improves Mac stability, performance and security, and is recommended for all users.
This update adds compatibility with Messages in iCloud, which allow you to store messages and their attachments in iCloud, and free up space on your Mac. To enable Messages in iCloud, open Messages Preferences, click Accounts, then select Enable Messages in iCloud.
The update is now available through the Mac App Store.
Update 06/01/2018 at 15:00
For those who prefer, here are the direct links to download: