watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-03-29T17:08:50Z. The update package is 336.79 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 04a4fea325584058d5bab135aad083b7f1ef3519.zip.