As you can see in the image below, flags for 'isBack4k60VideoSupported' and 'isFront4k60VideoSupported' were found under CAMCaptureCapabilities.
Recording in 4K may become more common with iOS 11. The new firmware brings High Efficiency Video Coding (HEVC), also known as H.265, delivering significant compression improvements over H.264. Apple estimates up to 40% better compression than H.264 in general use cases and up to 2x better compression than H.264 in iOS camera capture. This is going to mean significantly reduced files sizes when shooting 4K with the iPhone 7 or the upcoming iPhone 8.
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