By now, you are probably already downloading and/or installing the new Windows 10 build 10049. If you are an app developer, Microsoft is urging you to NOT download the build from the fast ring just yet, due to an issue with Visual Studio 2015 preview.
“There are 2 issues using Visual Studio 2015 preview on this build: The emulators will not boot and you won’t be able to deploy a Windows Universal app to the Mobile emulator. The XAML designer in VS and Blend will crash when opened. If you are a developer using these tools today to develop Windows Universal apps and need this functionality to work – we recommend switching to the Slow ring until we release a patch to fix these issues,” Microsoft stated in an official blog post.
Microsoft recommends waiting until a patch is released. Likely within a week or so, this build will be available to those of you on the slow ring, accompanied with some patches to critical bugs, like the one involving Visual Studio 2015 preview. If you are not an app developer, go play with Windows 10 build 10049 and let us know how much you like Spartan.