watchOS 5.1 (build 16R5568d) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-02T17:14:39Z. The update package is 779.59 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: 37d8660850e63f66111355f15f3373e00db69db2.zip.