watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-15T17:09:47Z. The update package is 777.67 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: caaa9c0086d8cf53714a933c9aa109bcc84fa3d4.zip.