Windows Phone 8.1 release date: Microsoft’s update to it’s mobile OS has reportedly reached Milestone 3, according to a report by WinBeta. The Windows-focused tech site says that it’s unsure how long the build has been in development stage, but one thing is that it means that Windows Phone 8.1 is closer to RTM and it’s scheduled spring 2014 release.

WinBeta says that according to Nawzil, who has been behind a number of Windows Phone leaks in the past, the Windows Phone build 8.10.12247.0 marks the first build of Milestone 3. It is uncertain when the build was compiled, so it’s possible that it could be very old.

The release of the new build will not affect current users of Windows Phone 8, but for enthuiasts and developers waiting for the Windows Phone 8.1, it means that it’s on its way. Win Beta notes that they don’t know how many Milestones the Windows Phone team has planned, but usually a version of Windows has three milestones before hitting Beta. It will then eventually go into RTM.

Win Beta reported that the information came from the FB Pages Manager app, a popular app to manage your Facebook Page. In a snapshot by Nawzil, Windows Phone 8.1 has shown up in the analytics, giving a hint that it’s nearing an official release.

One of the newest features expected Windows Phone 8.1 is “Cortana,” known as Microsoft’s version of Siri. The digital personal assistant will replace the Bing search option for Windows Phone and the like.

According to the International Digital Times, Windows Phone 8.1 may also feature separate volume controls, allowing users to control ringtone volume and media volume separately. There may also be Bing Smart Search. It’s expected that the full features of the new mobile OS won’t be seen until the Build Developer Conference in April, where many are hoping to hear the official release of the Windows Phone 8.1