watchOS 4.3 (build 15T5209a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-12T20:07:35Z. The update package is 374.69 MB. This is a delta (partial) update that requires 4.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 414d0c27a6b9abe3463386ddb6c1a3b6c1e0e734.zip.