There have been murmurs of a 4K Apple TV and even hints of 4K HDR videos on iTunes, but now we have evidence tying it all together. Remember that incredibly revealing HomePod firmware? Developer Guilherme Rambo has sifted through it to discover references to both 4K and HDR support in an upcoming Apple TV model. And the HDR support is particularly broad, too. The media player's code mentions support for Dolby Vision, HDR10 and Hybrid Log-Gamma formats, so the odds are that HDR's enhanced picture quality will be available even if your TV only has limited compatibility.
Apple certainly isn't the first to make a media hub with HDR support. Roku supported the technology nearly a year ago, for example. However, competitors sometimes only support one format (Roku's boxes insist on HDR10). The Apple TV may have a small edge simply because it should support HDR no matter which TV or media services you use.
There's one more tidbit in the firmware, although it's not necessarily a smoking gun. Jeffrey Grossman has noticed that there's a reference to "Gizmo" (the codename for the Apple Watch) supporting an embedded SIM, backing rumors that the next Apple Watch will have a cellular data option. A "radio bundle" mention might support the claim, too. We'll likely have to wait until the fall (or at least, another code discovery) to know for sure, but don't be surprised if future Apple wristwear can hop online without any kind of local wireless connection.