watchOS 4.3 (build 15T5165e) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-01-25T18:04:38Z. The update package is 350.94 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 92694ca242da080992acdf82ae1ee64d8782cb52.zip.