watchOS 5.3 (build 16U5566a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-07-09T17:19:30Z. The update package is 135.88 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: 07659d6d329cd509eb74c3d6b56b1df02b90ae88.zip.