watchOS 4.3.1 (build 15T5545b) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-04-16T17:04:40Z. The update package is 362.31 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 1d033babcfd98cb1f223b854be8488d6c45c4f7e.zip.