watchOS 5.1 (build 16R5589c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm, LTE), released on 2018-10-22T17:20:04Z. The update package is 177.89 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: cf5741de534bb16aebc648a58e794c939c0fc826.zip.