watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-02-21T18:12:11Z. The update package is 371.61 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: f120b629c762ac14bf5162f20343c2a224ebf299.zip.