watchOS 4.3 (build 15T5165e) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-01-25T18:04:42Z. The update package is 391.02 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: e3ff669ef503911191ec6d825fa8ec2f17ce4ade.zip.