watchOS 4.3 (build 15T5199f) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-03-06T18:08:27Z. The update package is 172.99 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: 4476625b8669c5e5fea04f86264128cc1ab2fbe4.zip.