watchOS 4.3 (build 15T5176c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-02-07T18:10:03Z. The update package is 128.17 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3a02ca556b32b29310f585a47404d2930c50c486.zip.