watchOS 4.3.1 (build 15T5555c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-01T17:06:58Z. The update package is 183.4 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: 1b573c1ff136d7ea0b4fa8db24a5788e590bf787.zip.