watchOS 4.3.1 (build 15T567) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-05-29T17:09:17Z. The update package is 332.34 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: b683678a396c48a443823155352a4720ef61fa98.zip.