watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-10-22T17:19:24Z. The update package is 778.72 MB. This is a delta (partial) update that requires 4.3.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2551bd52f8e29f3ac848ed8ab06c685a660540ea.zip.