watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-02-21T18:11:51Z. The update package is 334.83 MB. This is a delta (partial) update that requires 4.2.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: be5451dd7304043d734fec03cd4520c8da81a2ec.zip.