watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2019-06-24T17:24:59Z. The update package is 139.24 MB. This is a delta (partial) update that requires 5.2.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 5f677b32edbc52cec9ddea034b6cfce56abb6846.zip.