WatchOS

watchOS is the operating system software of Apple Watch, derived from iOS. The software can be updated by a paired iPhone with the Apple Watch app or directly from the Apple Watch. The current version of watchOS is 6.2.6.

watchOS 1 History
watchOS 1 was introduced with the original Apple Watch on April 24, 2015.

watchOS 1.0

 * Based on iOS Version 8.2
 * Release Date: April 24th, 2015
 * Build Number: 12S507

watchOS 1.0.1

 * Based on iOS Version 8.3
 * Release Date: May 19th, 2015
 * Build Number: 12S632

watchOS 2.0

 * Based on iOS Version 9.0
 * Release Date: September 21st, 2015
 * Build Number: 13S344

watchOS 2.0.1

 * Based on iOS Version 9.1
 * Release Date: October 21st, 2015
 * Build Number: 13S428

watchOS 2.1

 * Based on iOS Version 9.2
 * Release Date: December 8th, 2015
 * Build Number: 13S661

watchOS 2.2

 * Based on iOS Version 9.3
 * Release Date: March 21st, 2016
 * Build Number: 13V144

watchOS 2.2.1

 * Based on iOS Version 9.3.2
 * Release Date: May 16th, 2016
 * Build Number: 13V420

watchOS 2.2.2

 * Based on iOS Version 9.3.3
 * Release Date: July 18th, 2016
 * Build Number: 13V604

watchOS 3 History
watchOS 3 was announced at the 2016 Worldwide Developers Conference.

watchOS 3.0 Beta 3

 * Based on iOS Version 10.0
 * Release Date: July 18th, 2016
 * Build Number: 14S5290d

watchOS 4 History
watchOS 4 was announced at the 2017 Worldwide Developers Conference.

watchOS 5 History
watchOS 5 was announced at the 2018 Worldwide Developers Conference.

watchOS 6 History
watchOS 6 was announced at the 2019 Worldwide Developers Conference.

watchOS 7 History
watchOS 7, expected to be announced at the 2020 Worldwide Developers Conference, will reportedly introduce a "Kids Mode" that uses different metrics for activity tracking of young users.