watchOS 5.0 (build 16R5313d) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2018-07-03T17:11:03Z. The update package is 583.23 MB. This is a delta (partial) update that requires 4.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 905e6d488df175548a71c813c389245bd3532f8c.zip.