watchOS 4.3.1 (build 15T5565a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-05-07T17:23:35Z. The update package is 361.79 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 33de0d16d8c6413506edf7e880aa45f64ad70972.zip.