watchOS 4.3 (build 15T5165e) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-01-25T18:04:37Z. The update package is 352.22 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: 60bc8e5ad262216126c56258e4a63bae2edb4e6a.zip.