watchOS 5.2.1 (build 16U5101c) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-04-22T17:12:53Z. The update package is 174.61 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: 31489096cacd2e5ff4f7151a9909449072175738.zip.