watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-10-30T17:21:11Z. The update package is 974.32 MB. This is a delta (partial) update that requires 3.1.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3f8921a976a2e646403ac6a0ab3265c5046d5181.zip.