Microsoft has published a list of features that are available for UWP apps on the Xbox One, as well as those that are not supported. In that documentation, it refers to the Xbox One as running Windows 10 version 1607.
Xbox runs Windows 10, version 1607, which means that it shares the same core operating system as other devices in the Windows 10 family: desktop, mobile, and HoloLens. But, because this is the first release of the Universal Windows Platform (UWP) on Xbox, there are some feature areas that haven’t reached the same level of support on Xbox as they have on other devices. In this topic are details on some of the feature areas that your UWP app might use that don’t currently function as fully on Xbox. All APIs are callable and will fail gracefully if they’re unsupported. As we flight and service Windows, we’ll continue implementing, testing, and bugfixing until all of the Universal device family API surface is fully operational on Xbox.
It's very likely that version 1607 refers to the Redstone (Rs1) update, which was previously thought to be arriving in June. It's also worth noting that Redstone 2 (Rs2) has been pushed back to Spring 2017, so Rs1 is the only major version number change that we're likely to see this year.
Windows 10 version numbers are "yymm", meaning that it shows the year and then the month. For example, verson 1511 meant the year 2015 and the month of November. Because Redstone will be version 1607, it stands to reason that Microsoft's current plans are to ship the update in July.
The documentation also notes that apps using APIs introduced in version 1607 will not be accepted into the Store until the Preview period is over.
Of course, we're just hours away from the Build keynote, where all (or most) of our questions will be answered. In the meantime, check out our preview!