watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch (42mm), released on 2018-02-21T18:11:22Z. The update package is 652.02 MB. This is a delta (partial) update that requires 3.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a14419cc4d68f509653d0c6d5932553cb08bee73.zip.