watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-10-09T17:11:58Z. The update package is 391.11 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: 2d720f162a47f1f5f0cd609c6618781b192640d8.zip.