watchOS 4.3.1 (build 15T5535b) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2018-04-02T17:13:14Z. The update package is 145.58 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 24c3fb50352bbbe14635a71cf99dc855bf8cebfd.zip.