watchOS 4.3 (build 15T5209a) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2018-03-12T20:07:15Z. The update package is 325.67 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: 51fb37e3bb1170afe0f4ff8f174c4b4504bda142.zip.