watchOS 4.3 (build 15T212) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-29T17:09:13Z. The update package is 362.34 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: a83db49ce5f938ad830d738b493b0a0d8bde1cdf.zip.