Microsoft has reportedly wrapped up the development of Windows Phone 8.1 and released it to its partners, so OEMs can test it and prepare it for devices.

New handsets running the upcoming version of Microsoft's mobile operating system, Windows Phone 8.1, are expected to hit commercial availability as early as next month.

Microsoft should take the wraps off its latest OS version at its BUILD 2014 developer conference early next month, on April 2-4, and some devices running the new Windows Phone 8.1 are also expected to debut at the same time.

After seeing various leaks recently trying to paint a picture of what to expect from Windows Phone 8.1, a new report now claims that Microsoft has finished testing the OS and has released it to OEMs.

The latest news comes from Windows Phone Central (WPCentral), which claims that the final build of Windows Phone 8.1 still has a few bugs, but it has nonetheless reached device makers. According to the publication, the first few devices running the new Windows Phone OS version will launch toward the end of next month.

"Through various sources we've been able to verify that starting Wednesday, April 23^rd, new phones running Windows Phone 8.1 will be available," WPCentral reports. "It's not clear which phones those are, but presumably the Lumia 630, Lumia 930, and Samsung ATIV SE (for Verizon) are top contenders. We're also supposing that this is for US markets although it's not known at this time."

All three of these purported devices have leaked on several occasions so far. The Nokia Lumia 630 is expected to launch as a mid-range offering, with several neat specs and features and a budget-friendly price tag. The Nokia Lumia 930, meanwhile, is believed to be the highly-anticipated international version of the top-notch Nokia Lumia Icon, which is currently available only in the U.S. as a Verizon exclusive. Lastly, the Samsung ATIV SE has leaked with a design nearly identical to the Galaxy S4, along with high-end specs and features on board. All three handsets have been rumored to debut at Microsoft's BUILD 2014 conference, alongside the new Windows Phone 8.1.

If such rumors turn out to be true, these devices will debut next week and go on sale toward the end of April. Devices running Windows Phone 8 are also expected to be able to upgrade to Windows Phone 8.1 seamlessly, but it's not confirmed at this point.

"As to when those official over-the-air (OTA) updates will go out, it's not clear. Official updates for individual phones are slightly more complicated due to the corresponding firmware that needs to be developed and the added hurdle of carrier testing," adds WPCentral. "Ultimately, it is the carriers who will roll out the updates and like previous ones that could take months. Luckily if you want Windows Phone 8.1, you can have it within the next 30 days."