watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-03-29T17:09:01Z. The update package is 324.17 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: 7df5e038f214bb52ceb6e0b3a6bc99150f955e33.zip.