watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-15T17:09:51Z. The update package is 431.88 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: c849aca8b26a83b7c4670ab9ff324762356f0815.zip.