watchOS 4.3.1 (build 15T5545b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-04-16T17:04:25Z. The update package is 88.69 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: 17b3a0e3443b272a20af888b72f770c3dbf1efe0.zip.