watchOS 5.1 (build 16R5568d) is an official Apple over-the-air update for the Apple Watch Series 3 (42mm, LTE), released on 2018-10-02T17:14:51Z. The update package is 780.52 MB. This is a delta (partial) update that requires 4.3.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 0b36dd2a58586341cda10ea8034269c6fe70708d.zip.