watchOS 5.2.1 (build 16U5091b) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-04-08T17:12:33Z. The update package is 443.13 MB. This is a delta (partial) update that requires 5.1.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 3983e49e9e1e19bd3cc7696dbf2de864cc57ade2.zip.