As always, Gabe Aul has this description in his blog post on Blogging Windows.
I wanted to give you an update on what to expect with Windows 10 Mobile Insider Preview builds over the next few weeks and into next year.
As our partners and Microsoft ship new Windows 10 mobile devices and existing devices are upgraded to Windows 10, all of our users will start to see more updates coming through Windows Update. These will be addressing feedback we receive from our Windows Insiders and new Windows 10 users.
We have received a lot of useful feedback from our Insiders on our last Windows 10 Mobile Insider Preview build 10586. While this is the same base build that we are shipping with new Windows 10 devices, we are continuing to address feedback on the upgrade experience from Windows Phone 8.1 as reported from Windows Insiders.
Today we are releasing our first Cumulative Update to the Windows 10 Mobile Insider Preview Build 10586 to Insiders that begins addressing this feedback. The first thing you will notice with this Cumulative Update is it will use the minor version for differentiating between each version as these builds only contain fixes to the Windows 10 Mobile Insider Preview build already in the Fast and Slow rings. So this build will appear as 10586.29.
We are also taking this opportunity to onboard some new devices in the Windows Insider Program to receive these updates. These devices will be added early next week, along with an update to the Windows Device Recovery Tool that resolves detection issues on these devices.
Additional devices available to Windows Insiders early next week:
Microsoft Lumia 550
Microsoft Lumia 950
Microsoft Lumia 950 XL
Feedback we have addressed includes:
You will see additional improvements in upgrade experience, including devices with limited free space, map rendering on update, and RCS enabled device settings.
Improved application backwards compatibility for Windows Phone 8.1 Silverlight applications.
Edge performance and stability has been improved. Auto-completion has been updated to allow user to more easily edit the end of the URL in the address bar.
Additional Bluetooth stability improvements.
We have resolve issues on switching the active cellular connectivity profile on Dual SIM devices.
Data profiles are now correctly restored in the out of box experience that would prevent some devices from sending or receiving MMS messages.
As always please keep sending on your feedback.