watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-03-29T17:08:20Z. The update package is 674.09 MB. This is a delta (partial) update that requires 3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7e2cb4c0694e8a9acbbdd3af59d4bd842aafc767.zip.