watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-03-06T18:08:29Z. The update package is 375.25 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 0248deb7126711f0aabac327849217092c71dc8b.zip.