watchOS 5.1.1 (build 16R6600) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-11-05T18:05:39Z. The update package is 525.9 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: 6954157383cbb54a4c353feb9e0601fed53c6c06.zip.