watchOS 5.1 (build 16R5577c) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-09T17:12:04Z. The update package is 617.57 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: a179352cb1e3cbf8d262f1b2d7258ef468db85ea.zip.