watchOS 5.3 (build 16U5558b) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm), released on 2019-06-24T17:25:14Z. The update package is 157.32 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: 9ae28a251aafdf7356475097d056f6df8dce0fee.zip.