watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-06T18:07:51Z. The update package is 306.5 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: 54e081bc3863cbb764354b1d14dafde3622c88b5.zip.