According to Apple's documentation, the iPhone 7 Plus back camera (the wide one) can take photos at up to an ISO of 1716. But when I try to take a photo at that ISO, I instead get 1600.
I tried printing AVCaptureDevice.activeFormat!.maxISO, and it's indeed 1716.
I tried this with a third-party app (ProCamera), and the same problem manifests there.
How do I take a photo at ISO 1716?