This build was released on 2013-06-25 through MSDN (screenshot). Later on, it became publicly avaliable through Microsoft Technet Evaluation Center. First it was thought to be released alongside the client build on BUILD 2013 at 2013-06-26, but it came a day earlier. On the same day, System Center 2012 R2 Preview was also released. It is the first leaked build to have the new start button.