watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-03-06T18:08:31Z. The update package is 360.01 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: d23e6c39323ea5b7c3696e44f77439ed3b34679d.zip.