watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-05-01T17:06:33Z. The update package is 131.06 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: 4430f38376cce11afd67d2445ea5c7f1e9db1eb1.zip.