According to Kotaku, three anonymous sources suggest that there will be two new Xbox One consoles coming out in the next two years. This supports the recent rumors that both the PlayStation 4 and the Xbox One will be receiving substantial hardware upgrades in the near future.
The rumors state that the first console will be released this year, and it will be a much smaller console equipped with a 2 TB hard drive. The second console will launch next year which will reportedly have a more powerful GPU that is capable of running VR in addition to the ability to display 4K video. While the sources are apparently credible, Microsoft has given no official word in response to the rumors.
It is likely that we will hear more about the validity of this leak at E3 in the next few weeks.