watchOS 4.3 (build 15T5165e) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-01-25T18:04:49Z. The update package is 341.23 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: 4a0b9154a1f7417640c892f1612fbbc595560632.zip.