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Microsoft releases new Windows 10 Mobile test build that's likely RTM

Microsoft has made Windows 10 Mobile build 10586, its latest preview and likely its RTM version of its mobile OS, available to Insiders on the Fast Ring.

On November 18, Microsoft rolled out its latest Windows 10 Mobile preview build to Windows Insiders on the Fast Ring.

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That build, No. 10586 (the same build number as the RTM version of the Windows 10 November Update for PCs, a k a "Threshold 2") is likely also the RTM version of Windows 10 Mobile.

(Yes, Microsoft no longer uses "RTM" to designate the major final builds of Windows and major Windows updates. But many of us tracking them still do.)

Microsoft officials have not said 10586 is the RTM build of Windows 10 Mobile. It's interesting, however, that Microsoft started the Windows 10 Mobile lifecycle clock ticking earlier this week, as noted by Stanislav Zhelyazkov on Twitter.

According to Microsoft's support page, Windows 10 Mobile for Business and Windows 10 Mobile for Consumer's support-lifecycle start dates were both November 16, 2015. Mainstream support for both operating systems ends January 8, 2019. Extended support dates aren't yet specified but will be some date at least three years after the lifecycle start date, according to the release notes.

The Windows 10 Mobile 10586 preview build includes more fixes and reliability fixes. It fixes problems some were having with the Start experience after upgrading and restoring. It allows users to set default save locations and now reflects correctly current storage settings. Microsoft also says the new build enables users to move apps to SD cards without having apps crash. The build also is said to lessen the resuming and loading of text when switching apps.

Improvements to the Messaging + Skype app are also available alongside the latest build. And apps and games should download from the Store more reliably, according to yesterday's blog post outlining what's in the build.

Yesterday's post cautions testers that a bug in the previous test build, 10581, causes file systems to become partially corrupted after doing a factory reset of phones. The blog post includes instructions for working around this issue.

"We highly recommend that you make sure you do a backup your phone *before* upgrading to Build 10586 due to this bug," said Windows Insider chief Gabe Aul. "Additionally, you can also recover your phone by using the Windows Device Recovery Tool to go back to Windows Phone 8.1 and then upgrade to Build 10586."

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Another caution: Deploying Silverlight apps through Visual Studio to your phone still won't work in this build, but this issue will be fixed with the release of Visual Studio 2015 Update 1 on November 30.

Microsoft will begin selling the first of its new Lumia phones, the 950, on November 20 through AT&T in the U.S. The Lumia 950 and 950 XL are expected to run and/or be immediately upgradeable to Windows 10 Mobile Build 10586. Microsoft officials have said most existing Windows Phone 8.1 users will be able to upgrade to the final Windows 10 Mobile build starting in December.

As a reminder, Windows 10 Mobile isn't just the newest Windows 10 phone operating system. It also will run on new (not already available) small Intel- and ARM-based tablets in case any OEMs (or Microsoft itself) want to build such devices.