watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-10-09T17:11:53Z. The update package is 408.98 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: 2a9570eaa9709b77ef5ec337550827ca7a4d4ec5.zip.