Microsoft will reportedly announce Windows Threshold, also known as Windows 9, in April of this year.

Paul Thurrott reports that Microsoft will announce the successor to Windows 8.1 at BUILD 2014, citing the website's "sources." The operating system has been codenamed Windows Threshold but will likely be released as Windows 9.

"If all goes according to early plans, Threshold will include updates to all three OS platforms (Xbox One, Windows and Windows Phone) that will advance them in a way to share even more common elements," ZDNet reports.

Windows 9 is being developed without the help of Steven Sinofsky, former President of the Windows Division at Microsoft, who left the company after the release of Windows 8 in Nov. 2012. Microsoft is reportedly taking this opportunity to start a new "vision" and era for Windows.

"Don't expect anything that grandiose, but the Windows team believes it needs to hit a happy middle ground between the KGB-style secrecy of the Sinofsky camp and the freewheeling 'we can do it all' days that preceded that," Thurrott said.

Despite these plans, Windows Threshold has not begun development yet, reportedly. Apparently, development will not begin until after the BUILD 2014 conference in April. As a result, developers will not be receiving an alpha version of the new software at the conference.

According to reports, Windows Threshold aims to improve the "Metro" design language. Microsoft also is rumored to be planning three different Threshold milestone releases.

"It's unclear what these releases will be called (Beta, Release Candidate, etc.) or which if any will be provided to the public," Thurrott said.

Windows 9 is expected to be released in April 2015.

Microsoft is also expected to discuss plans for a new Windows Phone as well as Xbox developments at BUILD 2014.

An update to Windows 8.1 will come this year. The update will come as a service pack/feature pack-type update titled Update 1. Predictions say the update will come in April of this year, as will Windows Phone 8.1.