watchOS 5.2.1 (build 16U5110a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-04-29T17:38:37Z. The update package is 448.75 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: a7da5eec01b157c2e48691676abe0eb5f59c5afd.zip.