watchOS 4.3 (build 15T5209a) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-12T20:07:01Z. The update package is 319.67 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: b86092e0647fd4a965cfdd065910c877adb64c03.zip.