watchOS 4.3.1 (build 15T6567) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-05-29T17:09:13Z. The update package is 64.34 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: 5e03c872670df7698f56af83ae43e1f9bd9cfdde.zip.