watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-01T17:07:03Z. The update package is 128.58 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: 8e551b09c5d1c38a56c548af383151649d72102b.zip.