OTA firmwares cannot be restored to. IPSW Downloads collects them for potential future use. They might also be useful if you're doing research.
| ✗ | Apple Watch Series 2 (38mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 1fabfb208a8d14c511025fc13406c1603efb539b.zip |
| ✗ | Apple Watch Series 2 (42mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 4aeab713aa7bc684d96d7dbecb76379ed554ffa5.zip |
| ✗ | Apple Watch Series 1 (38mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 2686fb7018b90af5e61bed4f9509089fa82ef921.zip |
| ✗ | Apple Watch Series 1 (42mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | a994a1d0ce193ce955ab6ddeae0b72e86722be47.zip |
| ✗ | Apple Watch Series 3 (38mm, LTE) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 23244b7a8bab5add94bb1f95cd268ddc91513c56.zip |
| ✗ | Apple Watch Series 3 (42mm, LTE) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | c8d53f245640e5fca4319390b41553cfbd878cfd.zip |
| ✗ | Apple Watch Series 3 (38mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 8813240cb7d9157ed84546ba4e6c65771d721825.zip |
| ✗ | Apple Watch Series 3 (42mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 20e73e126a4cf8b15b2b8df350c570b4876b93b5.zip |
| ✗ | Apple Watch Series 4 (44mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | aa857b151ac0805255ab832fb4c5b4aad4a4c655.zip |
| ✗ | Apple Watch Series 4 (40mm) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | 83f1a5e427cecd48119de3e87c08ea37899fb4c0.zip |
| ✗ | Apple Watch Series 4 (40mm, LTE) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.4 GiB | 9d18cfc3598fe218f3016fb0f133c5b58b720928.zip |
| ✗ | Apple Watch Series 4 (44mm, LTE) | watchOS 5.3.1 (16U600) | August 26, 2019 | 1.3 GiB | e863f515afd29f4869fa70d0e900475bc3f83b75.zip |