watchOS 4.3 (build 15T5176c) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-02-07T18:09:53Z. The update package is 95.69 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: bb48a682c05e96e645bc3e360c82c7ee87860820.zip.