watchOS 5.1 (build 16R5559d) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-09-18T17:23:11Z. The update package is 555.44 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: 39420c19f74f113268c3d7af55836c2fcd146c22.zip.