watchOS 5.2.1 (build 16U5079d) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-03-28T17:11:00Z. The update package is 148.28 MB. This is a delta (partial) update that requires 5.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3f0370423cc28c8b86dd0deaef9a6eacc690b024.zip.