Preview at WWDC likely in June, followed by September launch.
Apple Says Apple Watch Series 3 Lasts Up to 7 Hours When Streaming Apple Music Over LTE
While all Apple Watch Series 3 models are rated for up to 10 hours of battery life when playing music from the watch's built-in storage, Apple says the device gets up to seven hours of battery life when streaming Apple Music with LTE.
Apple also says the Apple Watch Series 3 has up to five hours of battery life when streaming live radio with LTE. watchOS 4.1 features a new Radio app with access to Beats 1 and other Apple Music radio stations.
For outdoor sessions with the Workout app, the Apple Watch Series 3 is rated for up to three hours of battery life with streaming audio, GPS, and LTE. That's one hour less than an outdoor workout without streaming audio.
Apple says battery life varies by use, configuration, cellular network, signal strength, streaming quality settings, and many other factors.