WatchOS 4

watchOS 4 is the fourth major release of watchOS for the Apple Watch series developed and distributed by Apple Inc. It was announced at the 2017 Worldwide Developers Conference alongside iOS 11, tvOS 11 and macOS High Sierra.

Product history
watchOS 4 is derived from iOS 11; both were announced on June 5, 2017 during the keynote address at WWDC 2017, when it became available to developers. It was released to the public on September 19, 2017.

Supported models

 * Original Apple Watch, also known as Series "zero" (limited support)
 * Apple Watch Series 1
 * Apple Watch Series 2
 * Apple Watch Series 3 (included with initial release)