watchOS 5.3 (build 16U5526f) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2019-05-15T17:11:20Z. The update package is 165.34 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: 0c3dd94cc901c118df257899c52d6be49466febe.zip.