Early reviews of the new Apple TV 4K highlighted that Apple will add Rapid Media Switching Variable Refresh Rate (QMS VRR) support to tvOS via a software update. QMS VRR prevents momentary interruptions when switching between playing content with different frame rates. As he emphasized TechCrunchUsers who have already enabled the “Content Matching” setting for the framerate may already be familiar with it as it “happens almost every time you start streaming a live show or movie from most apps”. From Apple TV 4K review Boundary :

The third-generation Apple TV 4K has another piece of the future: A software update later this year will add support for what’s known as QMS VRR. This allows compatible TVs to switch between different frame rates without black screens or noticeable picture interruptions. You ask how many TVs are working with QMS VRR? Zero for now. But you’ll start to see them hit the market next year; Stay tuned for news about this feature at CES. I’ve never been more bothered by a brief jitter when changing frame rates, but I won’t miss it either.

It’s worth noting that QMS VRR doesn’t prevent dimming when switching between color spaces or HDR content. The new video quality feature will be added to tvOS via a software update. It’s unclear if this feature will make its way to the second-generation ‌Apple TV‌ 4K, but since last year it might make sense for the device to offer high frame rate HDR content up to 60fps and HDMI 2.1 support.