Microsoft is planning an event for the next Xbox in May according to The Verge. The event was reportedly scheduled for April but had to be pushed back. They claim that they understand that the date May 21st is accurate. The sources familiar with the console claim that the event will be at a small venue with a focus on giving the first details on the new Xbox, and Microsoft's plans for the brand in 2013. On the console itself the sources say the software will be based on Windows 8.
Recent rumours have suggested that the next Xbox will require a connection to the internet at all times which has caused a bit of a backlash from users.
Source: The Verge