watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-03-29T17:08:56Z. The update package is 324.3 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2639e81435cc050796b610b7b4d39730c41a97bc.zip.