watchOS 4.3 (build 15T5176c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-02-07T18:10:02Z. The update package is 343.72 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: d34a88f06ff7dc647faada9462ae2822c79c9513.zip.