watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-22T17:19:57Z. The update package is 160.31 MB. This is a delta (partial) update that requires 5.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: ea9f7d77b13b2c143d936ad18936e368578019d0.zip.