Microsoft, last Friday, has released a new update for the Windows Phone 8 SDK, that works both with Visual Studio 2012 (it’s required, at least, the Update 2 installed) and Visual Studio 2013 Preview. The update doesn’t include any new API, but it just add 4 new emulator images, aligned with the GDR2 update of the operating system. This way, you can test your apps against the latest Windows Phone release (even you shouldn’t expect to find compatibility issues), that, other than adding new consumer features, it fixed a couple of bugs in the API (the most noticeable one is about the HttpWebRequest, that now is able to work properly with cookies).
You can download the new update from here: the file size is about 1 GB.