watchOS 5.1.1 (build 16R600) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-11-05T18:06:28Z. The update package is 748.81 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: ca7f0dd075c27dbb5589375debdf69e021d9829e.zip.