watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-30T17:21:19Z. The update package is 782.53 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: 9f0420b97ac206886b32dd851424576e8e08d5ee.zip.