watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-05-01T17:06:32Z. The update package is 139.64 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: 6e652055cf352f2875ab225d0cc2cc840971079f.zip.