watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-03-29T17:08:47Z. The update package is 685.88 MB. This is a delta (partial) update that requires 3.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 89d2a4ba2728d6a0fcb8efbdb7a5893595ae8c59.zip.