watchOS 4.3 (build 15T5187e) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-02-21T18:12:11Z. The update package is 371.65 MB. This is a delta (partial) update that requires 4.2.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 7a3be07a0b5ada61f6c444c80fd2b90c7af7f55d.zip.