Yep, Cortana, UWP, dev kit support and a new universal store. Pretty big update. I hope this comes with keyboard and mouse support.
Dev kit is available in preview form starting today, but make sure to read the instructions and limitations!
http://www.polygon.com/2016/3/30/11318568/xbox-one-dev-kit
About the DevKit and Preview programs...
As you may have heard at the Microsoft Build 2016 conference today, there's a new Developer Preview program which allows anyone to turn their Xbox One console into a development kit.
Here are a few things to keep in mind if you're currently in Xbox One Preview and interested in joining Developer Preview:
If your console is currently enrolled in Xbox One Preview, you will not be able to join Developer Preview until you unenroll from Xbox One Preview.
Your console cannot be enrolled in both Xbox One Preview and Developer Preview simultaneously.
If you choose to join Developer Preview and leave at a later time, you will be eligible to rejoin Xbox One Preview.
Please keep in mind that Developer Preview is intended for developers; if you don't intend to use your console for development, joining Developer Preview is not recommended
.
You can find more information about Developer Preview below:
https://developer.microsoft.com/en-us/
After activating your console for the Developer Preview via the Dev Mode Activation App (Available in the Store), your console will update to the current Developer Preview OS version. (Note that this is an early look an upcoming System Update and you may run into issues during use.) Once updated, you’ll be able to flip your console to Developer Mode and back to Retail via the Dev Mode Activation and Dev Center apps. Retail games and app will not be available on your console while it is in Dev Mode and likewise, any apps and games you’ve created will not be available while in Retail mode.
To remove a console from the Developer Preview, you’ll need to deactivate your console from the Developer Preview. This can be done though the Dev Mode Activation app or online under your account in Dev Center. Doing so will result in a Factory Reset of your console and return it to the currently available OS version.
You can re-enroll your console into the Xbox Preview Program after you've deactivated it from the Developer Preview.