watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-01T17:07:04Z. The update package is 119.62 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 95bf5cab5fd3a8b634d7eb73add5e47262ae6b77.zip.