watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-16T20:09:31Z. The update package is 375.17 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: 91ea466d95b73f9f048975a2c87f8cb2ca737828.zip.