A few months ago, Microsoft announced their ID@Xbox program, designed to offer small game developers a way to self-publish on the Xbox One. At the time, Microsoft said that plans were in the works that would allow anyone with a retail Xbox One unit to turn it into a development hardware kit but details were not announced.
Now a YouTube video on the GameTuts channel has revealed a way to go ahead and turn any Xbox One into a development kit right now; the YouTube link has the full procedure.
Having said that, a post on Reddit from an unnamed but confirmed developer of Xbox One games says that the method in the video really shouldn't be used, stating, "Please don't mess with anything here for the time being, especially the sandbox ID. You risk putting your box into a boot loop."
The same developer later posted that he had no idea when Microsoft would officially enable development kits from Xbox One units, stating, "There are many concerns such as privacy, security, stability etc.., that need to be sorted out before we can allow anyone and everyone to simply sideload an app onto their box."
So there you have it. If you really want to, you can turn your new Xbox One into a development kit just for fun, but you run the risk of bricking it. If you really want to make games and self-publish them on the console, your best bet is to sign up for Microsoft's official ID@Xbox program.