watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm), released on 2018-03-16T20:09:54Z. The update package is 331.46 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: f9777f826060dbc351688f160057ea06968948ad.zip.