Windows 8.1 was publicly released in October 2013 and rumors are already rife that Microsoft has begun working on its successor, codename "Threshold."

According to ZDNet writer Mary Jo Foley, a couple of sources have confirmed that Microsoft's upcoming operating system, which will unify the three OS platforms - Windows, Windows Phone and Xbox One - via a series of updates.

"From what I've heard, Threshold doesn't refer to a single Windows OS -- not even the expected, converged hybrid comprised of the Windows Phone OS and Windows RT. Instead, the codename refers to the wave of operating systems across Windows-based phones, devices and gaming consoles," Foley says.

While Windows 8.x OS, Windows Phone 8 OS and the Xbox One OS share the common Windows NT core, Threshold promises to take it to the next level by supporting the "high value activities" whose aim is to promote the company's "One Microsoft" mission.

Foley goes on to add that Microsoft will launch Windows Phone Blue (aka Windows Phone 8.1) as well as release an update to WIndows 8.1 before Threshold sees the light of the day.

A Microsoft spokesperson responded with the standard boilerplate statement "We do not respond to speculations or rumors," when contacted by Tech Times. However, we won't be surprised if Threshold turns out to be true as Microsoft didn't have a good run with Windows RT, which caused confusion among OEMs and consumers alike. Foley promises that Threshold release is set for "spring 2015." Wonder whether Steve Ballmer, who's set to step down soon, will have any hand in it.

Shares of Microsoft were up 0.32 percent at $38.45 on the NASDAQ during late afternoon trading session on Monday.