watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-15T17:10:24Z. The update package is 160.22 MB. This is a delta (partial) update that requires 5.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 4ed32df924bc305e8bbde66fcb94340d345765e2.zip.