watchOS 4.3 (build 15T6212) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-03-29T17:08:39Z. The update package is 131.33 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4fe69275f1948b0029c2840d4e4afebaa15b175f.zip.