watchOS 4.3 can be downloaded through the dedicated Apple Watch app on the iPhone by going to General --> Software Update. To install the new software, the Apple Watch needs to have at least 50 percent battery, it needs to be placed on a charger, and it needs to be in range of the iPhone.
watchOS 4.3 introduces support for Nightstand mode when the Apple Watch is positioned in a portrait orientation, a feature that was previously only available when the watch was placed in landscape orientation on its side.
Today's update also reintroduces a much-desired feature that allows music playing on the iPhone to be controlled using the Music app on the Apple Watch.
In previous versions of watchOS, starting with watchOS 4, the Music app could only be used to control music playing on the watch itself. watchOS 4.3 returns pre-watchOS 4 functionality and once again allows you to select the music playing on your iPhone from the Apple Watch. With watchOS 4.3, you're also able to control playback and volume on the HomePod using the Apple Watch.
Other new features in watchOS 4.3 include a new charging animation when the Apple Watch is placed on the charger and a new app loading animation when opening up an app. You'll also now see your Activity data on the Siri watch face, and the battery complication more accurately reports battery life.
For more on the watchOS 4 operating system, make sure to check out our dedicated watchOS 4 roundup.