watchOS 4.3 (build 15T5165e) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-01-25T18:04:20Z. The update package is 313.43 MB. This is a delta (partial) update that requires 4.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7f3ea618df64f9ba6c863c3a3880e6ed36ee5d74.zip.