watchOS 4.3.1 (build 15T5567a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-05-14T17:14:23Z. The update package is 333.09 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: ab328c311843b39033be66581a96a632d407cda0.zip.