watchOS 5.1 (build 16R6591) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2018-10-30T17:21:56Z. The update package is 80.38 MB. This is a delta (partial) update that requires 5.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 8e568f9a283a0d5880fbd48e1374b651d71ef558.zip.