A new build of Redstone 2 for Windows 10 Mobile for Fast ring Insiders! It's a veritable bug-fixing fest and plenty of known issues are knocked on the head or worked around. The headline new feature is full support for DRM-free e-books in Edge, but it's the stability fixes which interest me most.

From the Microsoft announcement:

Today we are excited to be releasing Windows 10 Insider Preview Build 14977 for Mobile to Windows Insiders in the Fast ring.

Read EPUB books in Microsoft Edge on your phone: In addition to being able to read any unprotected e-book in the EPUB file format on your PC with Microsoft Edge – you can also read unprotected e-book in the EPUB file format with Microsoft Edge on your phone! When you open an unprotected e-book in Microsoft Edge, you will be taken into a customizable reading experience where you can change the font and text size and choose between 3 themes: light, sepia, and dark. As you read, you can leave bookmarks. To navigate through an e-book, you can use the table of contents or seek bar at the bottom of the browser. And you can also search for words or phrases and use Cortana to define specific words.

You can download and read unprotected e-books from places like Feedbooks, Project Gutenberg, Free eBooks (requires sign-up), ePubBooks (requires sign-up), Open Library and even our own Microsoft Press. Try out reading an e-book in Microsoft Edge on your phone and let us know what you think!

Other changes, improvements, and fixes for Mobile

• We’ve changed the rendering technology used for many types of UWP app content, so please provide feedback through the Feedback Hub if you notice any new visual glitches in UWP apps.
• Alarms sent by 3rd party alarm apps will now break through Cortana’s Quiet Hours – we appreciate all the app developers who logged feedback requesting this, keep it coming!
• We’ve removed the top-level option in Notification Settings to disable alarms on the lock screen – alarm reliability is a top priority for us, and we’ve found this setting was frequently enabled accidentally, without awareness that it would stop alarms from waking the phone when the phone was locked. For those who still wish to enable this setting, it’s will continue to be available under the per-app notification settings.
• Notifications from Settings can now be customized or disabled – option is available under Settings > System > Notifications > Settings
• We have enabled OAuth support for Yahoo Mail accounts. This will improve sync reliability for those accounts, and provide a secure experience while browsing your email.
• We fixed an issue where disconnecting and reconnecting a wired headset while watching a video might result the audio no longer working.
• We fixed an issue Insiders may have experienced where certain music apps would unexpectedly stop playing music after a single song.
• We fixed an issue where closing a tab in Microsoft Edge, exiting the app, and then relaunching it would sometimes result in Edge opening to a blank page with the closed tab’s web address in the URL bar.
• We fixed an issue where the Start Settings page wasn’t rendering when opened on external screen while using Continuum.
• We’ve made a number of translation improvements, including, for French (France and Canada) speakers, fixing a grammatical error in the “Don’t Forget!” text seen when shutting down the phone so it now says “N’oubliez pas”, and for Chinese speakers, fixing an issue where the option to clear the Chinese Input Method Editor’s input history was displaying in English rather than Chinese. If you see any other translations that aren’t as you’d expect, please log feedback – we’re listening!
• We fixed an issue where, if the setting to show notifications above lock had been turned off, booting the device and immediately checking the Action Center while the phone was locked could result in the Action Center not displaying any notifications after the phone had been unlocked.
• We fixed an issue Insiders may have experienced where the Camera app might not appear after using the hardware camera button while the screen was off or while on the Glance screen.
• We fixed an issue where Bangla (Bangladesh) keyboard text prediction might stop working after entering character followed by a vowel mark.

Known issues for Mobile

• Please avoid attempting to install new languages, keyboards, and speech packs on your phone. There is a chance these downloads may get stuck and not finish downloading. If you have existing languages, keyboards, and speech packs installed – they will carry over when you update to new builds. You can use Windows Device Recovery Tool to go back to Windows Phone 8.1 or Windows 10 Mobile, install any languages, keyboards, and speech packs you need and then update to the latest build in the Fast ring as a workaround.
• Windows 10 phones with 8GB of internal storage such as the Lumia 550 and 650 will likely receive an 0x800700b7 error when attempting to update to this build.
• System related notification toasts (e.g. Bluetooth, USB/Autoplay, etc.) do not work.

So some significant known issues then - this is the bleeding edge, mind you, so you knew the risks when you signed up! But, on the whole, that's a lot of issues addressed, and all very specifically this time for mobile - Microsoft continues to put a lot of attention into Windows 10 Mobile and we're now about four months from an official production roll out of this OS branch.

Of course, in the fulness of time we'll need a summary of what's new going from Redstone to Redstone 2 (Anniversary Update to Creators Update), but we won't have a full feature set or changelog for a while yet - this mobile OS has got legs, even if the number of licensees isn't overwhelming (though we had a new flagship device only recently). Settle down for the long haul, everyone....!

Anyone with an existing phone that's officially deemed Windows 10 Mobile compatible by Microsoft can join in the fun. The full list of phones includes Lumia 430, 435, 532, 535, 540, 635 (1GB RAM version), 640, 640 XL, 730/735, 830, 930, 1520, Icon, BLU Win HD w510u, BLU Win HD LTE x150q, and the MCJ Madosma Q501. Plus, of course, all the devices which have shipped with Windows 10 Mobile in the last year, of which the Lumia 550, 650, 950, 950 XL, Acer Jade Primo and HP Elite X3 are the highest profile.

In each case:

1. Upgrade to Windows 10 Mobile (if appropriate) using the Upgrade Advisor.
2. After at least one update cycle you should then be on the Anniversary Update (a.k.a. Redstone). Head into Settings/Update & Security/Windows Insider Programme
3. Join the Insiders programme and choose the 'Fast' level in the pick list.
4. Within a few hours your phone should be seeing the build mentioned above and you'll be running next year's mobile OS today. Fun, fun, fun....!