The new version number you'll apparently end up with is '10051' (it was '9941') and I'd estimate that we're still a good few months from a production-ready build, so don't expect too much in terms of stability or feature completeness. This Microsoft feature goes over the context...
Interestingly, the version numbering on the phone is totally different (go figure), so the phones report OS version 10.0.12534.56. No doubt it all makes sense at Redmond!
Thanks to Microsoft fixing their 'Partition stitching' issues (don't ask!), the device pool for which this new build is available has been widened significantly and now stands at:
- Lumia 1020
- Lumia 1320
- Lumia 1520
- Lumia 520, Lumia 525, Lumia 526, Lumia 530, Lumia 530 Dual Sim, Lumia 535, Lumia 532, Lumia 532 Dual SIM, Lumia 535 Dual SIM
- Lumia 620, Lumia 625, Lumia 630, Lumia 630 Dual Sim, Lumia 635, Lumia 636, Lumia 638, Lumia 640 Dual SIM
- Lumia 720, Lumia 730, Lumia 730 Dual SIM, Lumia 735
- Lumia 810, Lumia 820, Lumia 822, Lumia 830
- Lumia 920, Lumia 925, Lumia 928
- Microsoft Lumia 430, Microsoft Lumia 435, Microsoft Lumia 435 Dual SIM, Microsoft Lumia 435 Dual SIM DTV
Note the absence of the Lumia 930, Icon and 640 XL:
Unfortunately there is an issue with scaling on certain devices (930, Icon, and 640XL) which makes the UI too small to be usable, and we need to add code to support new scaling thresholds for these devices. That work is underway, so we expect to see support for them in the near future. I know some of you will be disappointed, but trust me that you want us to make that fix before we send it out to you.
The main changes for this Insider build over the previous one are detailed here, but in summary (with my emphases in bold):
- Added Project Spartan: An early version of Project Spartan is available in this flight. It uses our new rendering engine to give greater interoperability with the modern mobile web, and includes early versions of Reading View and Reading List.
- New mail and calendar apps: Outlook Mail and Outlook Calendar are the new built-in mail and calendar universal apps for Windows 10. These new apps bring a fresh UI, with a toggle to freely move between your email and calendar without returning to the Start screen.
Please note that to add or remove accounts in Outlook Mail and Outlook Calendar, you do so within these apps. The Email + accounts page has been removed from the Settings app.
- New Phone and Messaging apps: The Messaging app has a new visual design. You can also easily upgrade from a messaging conversation to a voice call with one click of the phone icon in the new app bar.
- New People app: The new universal People app has a new visual design.
- New Maps app: The first preview of our new universal Maps app on phone is now available. This includes the best maps, aerial imagery, rich local search data, and voice guided navigation experiences from both Bing Maps and HERE maps, integrated together for the first time into a single app for Windows.
- Updated App Switcher: Check out the updated app switcher by pressing and holding the back button on your phone to see your recently used apps. We’ve added support for landscape when invoked from an app being viewed in landscape. For large phones like the Lumia 1520, we’ve introduced a new grid layout so you can be more efficient at switching between apps. And we’ve extended the length of recently used apps to 15.
That's quite a changelog. The last one, letting you go back further in your apps history/'multitasking' could be very significant, I'm installing this build on our 1520 so will report back.
The new Maps application is interesting. Has the HERE team's code now been jettisoned, following HERE's gradual distancing from Windows Phone? It does seem so. When Nokia Maps started out (from Gate5), they were one of the only games in town, but mapping data is now ubiquitous for many countries, so it probably doesn't matter that much exactly where the 1s and 0s come from, as long as it all works. From my initial playing, it seems that the plan is to license the raw map data sets from HERE and others (including Zenrin, for Japan and other countries), but to have the application itself purely written and maintained by Microsoft, as part of Windows 10. Which makes sense.
I did try the 'Camera' app in this Windows 10 build and it's almost identical to Lumia Camera 5, including Rich Capture (HDR), at least in terms of functionality and look (if not performance, yet) so good to know that imaging isn't being forgotten in the development efforts.
As ever, there are some known issues too:
- There might be situations in which auto-upload of your Camera Roll to OneDrive may not be working. Please be sure to back up your photos especially if you need to use the Windows Phone Recovery Tool to go back to Windows Phone 8.1.
- The Office Hub has been removed from this build. You won’t be able to open Word, Excel, PowerPoint or OneNote files in this build. Preview versions of the universal Office apps will be available in the coming weeks.
- We are redoing how text messages are handled and processed by Cortana so in this build text messages cannot be read out over Bluetooth.
- After upgrade, some apps that have been installed onto a SD memory card will fail to launch. To fix this, uninstall and reinstall the apps.
- About 1% of the time, incoming phone calls may not play a ringing sound.
- Call + SMS filtering will not work after upgrade.
- For people upgrading their phone from Build 9941, there is a bug in which your phone’s MMS settings will be lost after upgrade. The new Messaging app doesn’t yet have the ability to re-enter these settings. You will need to use the Windows Phone Recovery Tool to go back to Windows Phone 8.1 and then upgrade to this build to get MMS working again.
- Also for people upgrading their phone from Build 9941, the tiles on your Start screen for the Camera and Photos apps may be missing or corrupt. You will have to unpin any corrupt tiles and re-pin the apps to your Start screen.
- On some phones, due to a scaling bug the dismiss button won’t be visible when an alarm is triggered. To stop your phone from “alarming “just touch the arrow and swipe up on the notification and off the screen to end the alarm.
- On phones with 512MB of memory, apps can randomly crash due to an issue with memory management.
- Flight mode cannot be enabled.
- Data connections can’t be disabled.
- You may need to re-pin the Phone app after upgrade.
- The Insider Hub is now included on Phone but may fail to launch on some phones.
PS. Note that if there's a catastrophic problem with the new preview, it's possible to get back to the previous Windows Phone 8.1 Update 1 using the Microsoft recovery tool here.