watchOS 4.3.1 (build 15T5535b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-04-02T17:13:27Z. The update package is 362.09 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: cb5246efed990604561149e338bc99af1367c0c2.zip.