Through an official blog post Microsoft has announced the release of Windows Phone SDK 7.8, to prepare the update ready for general public launch in near future.
According to Microsoft Windows Phone SDK 7.8 includes “two emulator images which enable you to fully test how your Windows Phone 7.5 app’s Live Tiles will look and behave when they are run on a device running Windows Phone 7.8.”
“Most importantly, any Windows Phone apps that you build using the Windows Phone SDK (with this update installed) still target and run on Windows Phone 7.5. This update simply makes it easier to test how your apps appear on devices running Windows Phone 7.8.”
You can find details of Windows Phone SDK 7.8 at source.