I've tested auto-HDR in a number of backward compatible games on a preview version of the Xbox Series X hardware. And it's a big benefit. Every game I tested maxes out at 1,000 Nits, which is a measure of luminance. When it comes to HDR, 1,000 Nits is a gold standard for the bright highlights in an image.
Watch on an HDR compatible device or screen if you can! With our early Xbox Series X preview, we wanted to show as many games as we can running on the system, so here's a look at a bunch of titles in a 4K 60 FPS HDR video!
Note: Looks like I made a mistake during my research for this video, Red Dead 2 runs locked at 4k resolution on One X and did not make use of dynamic resolution scaling.