In the summer of 2016, Microsoft introduced the Xbox One S, bringing support for HDR to the Xbox family for the first time. Now, after four and a half years, Google has implemented HDR video support into the YouTube app on Xbox consoles, as reported by FlatpanelsHD (via Windows Central).
HDR has become a fairly standard feature in modern TVs and every iteration of the Xbox since 2016 has supported it. YouTube itself also added support for HDR videos later that year, so it's certainly interesting that it took this long for those two things to come together.
It's not completely clear when the capability was added to the YouTube app, but FlatpanelsHD points out that it wasn't available on the Xbox Series X back in December. The report confirms HDR is working on both the Series X and the One S, and there's no reason why it wouldn't also work with the One X and Series S.
You'll need to make sure you have the latest version of the app for HDR to work, or you can download the app from here if you haven't yet. While HDR support in the YouTube app is good news, it doesn't look like it's working as well as some might hope just yet. The app only supports HDR in videos using Google's VP9, instead of adopting the more modern AV1 format, which has also been backed by Google. Hopefully, a future update will address that issue.