watchOS 4.3.1 (build 15T5567a) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-05-14T17:14:21Z. The update package is 48.76 MB. This is a delta (partial) update that requires 4.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 49bc6f7b3c42a028e4cb667ccd7eee98021428b1.zip.