watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-06T18:07:58Z. The update package is 134.44 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 763b1c10aea8b231a7a1f71f35b87442d3d9adeb.zip.