watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-02-21T18:12:01Z. The update package is 131.88 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: 38f4c031836e8139e89b22364b9be0e25156ed22.zip.