watchOS 5.1 (build 16R5584a) is an official Apple over-the-air update for the Apple Watch Series 2 (42mm), released on 2018-10-15T17:09:20Z. The update package is 578.05 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: 63e99a56861d16c8cc791209eeb6c26443169ab5.zip.