watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-03-16T20:09:38Z. The update package is 360.85 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 6bc4ac70337d517c24f2f75b06fe42b082f89d13.zip.