watchOS 5.3 (build 16U5537b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-05-28T17:12:21Z. The update package is 174.75 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: e8c7ac8331d9589e718ab125cd2c8b3813408df5.zip.