watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-10-09T17:11:55Z. The update package is 733.1 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: bea9b2dbe4257416d00e315d7a61758be2a5a21f.zip.