watchOS 4.0 (build 15R5365a) is an official Apple over-the-air update for the Apple Watch Series 1 (38mm), released on 2017-08-22T16:58:49Z. The update package is 1.06 GB. This is a full OTA update that can be applied from any compatible base version. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 9c42b41b015e3394d7c2ce0231450fa520e26758.zip.