watchOS 4.3.1 (build 15T5567a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-05-14T17:14:11Z. The update package is 361.81 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a8714008e07ea9c0c0b2eedf056adff3c1ba11c5.zip.