watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-02-21T18:11:25Z. The update package is 317.87 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: a5c62820dc1dc7f4a1d7e4164fbc368f2d837446.zip.