watchOS 4.3.1 (build 15T5545b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-04-16T17:04:28Z. The update package is 376.93 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: e3a793129a4a4cd95969212cf799f1a2dcbfae7b.zip.