watchOS 4.3 (build 15T5212a) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-03-16T20:09:02Z. The update package is 137.62 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: e84ec6c8acbba543e0d7854aa033bc5338711353.zip.