watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-06T18:08:24Z. The update package is 360.71 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: 5a440e99d5612e325b838944be3e7d4f1d8c635e.zip.