watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2018-10-09T17:12:13Z. The update package is 748.05 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: 9d57357ece4e9ceb52781f252e0b74c3ddbbe213.zip.