watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-03-06T18:08:43Z. The update package is 147.9 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: a56b474598dfd3514f3379bac91beca642f19fba.zip.