watchOS 4.3.1 (build 15T5545b) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-04-16T17:03:54Z. The update package is 308.38 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: 03846411836ec582275d48216057255703edc57f.zip.