watchOS 5.1 (build 16R5559d) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-09-18T17:23:07Z. The update package is 741.56 MB. This is a delta (partial) update that requires 4.3.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 88a3c7d7ba57f5135420d71d7a042c8632817a8a.zip.