This afternoon Apple has released macOS 10.13.4 in the Mac App Store, as the update comes after iOS 11.3, tvOS 11.3 and watchOS 4.3 was pushed out earlier this morning.
The update says users can expect to see support for external graphics processors (eGPUs), sorting of Safari bookmarks by name or URL, privacy changes and more. Note Business Chat in Messages is limited to the U.S. only, for now. The update also includes a wallpaper for download which was previously limited to the iMac Pro.
You can download this update by launching the Mac App Store and clicking on the updates tab.