watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-22T17:19:58Z. The update package is 160.25 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: fdace116f1044a9adc4e0679ec8950dd5938a103.zip.