macOS Sierra will download in the background and prompt users to install the update, when convenient, Apple confirmed to The Loop.
Apple will begin its auto-download of macOS Sierra randomly over the next week for its users. The update will download when it makes sense and only for Macs that support Sierra and have enough storage space.
Users can turn off the automatic updates in App Store preferences, and they can be manually deleted.
The headline features in macOS Sierra are Siri for the Mac, Apple Pay to the desktop, an updated Photos in line with the iOS 10 experience, iCloud improvements, and the new Universal Clipboard that allows copying and pasting text and images between iOS and Sierra.