Microsoft has made available its first Cumulative Update to the version of the Windows 10 Mobile operating system it delivered in November.

Microsoft delivered the update, which it is calling 10586.29, the evening of December 4. Microsoft officials are referring to the update as a Cumulative Update, rather than a typical preview build.

What's in 10586.29? According to Windows Insider chief Gabe Aul:

Improvements in upgrade experience, in particular for 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 improvements.

Updated auto-completion to allow user to more easily edit the end of the URL in the address bar.

Additional Bluetooth stability improvements.

Fixes for switching the active cellular connectivity profile on Dual SIM devices.

Fixes enabling data profiles to be correctly restored in the out of box experience that would prevent some devices from sending or receiving MMS messages.

Microsoft also plans to add some new Windows Phones to its list of devices which can run Insider Previews. The new devices, which will be added early next week, are:LG Lancet, Microsoft Lumia 550, Microsoft Lumia 950 and Microsoft Lumia 950 XL.

Update: Microsoft made the test build available to Insiders for these phones on December 7.

Microsoft officials have said existing Windows Phone 8.1 users should begin seeing availability of Windows 10 Mobile for their devices in December 2015.