watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 4 (44mm), released on 2018-10-09T17:12:26Z. The update package is 1.33 GB. This is a full OTA update that can be applied from any compatible base version. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: bd05a9a5827b9afec1a633d40e659c70062548fd.zip.