watchOS 5.1 (build 16R5568d) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-02T17:14:44Z. The update package is 433.83 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: 2609194f757eda3a09a08896213c50a6c39c9aaa.zip.