An update to Visual Studio 2013 is now available for download.
For more details see Visual Studio Team Blog, Brian Harry’s blog, and Somasegar’s blog.
Official KB article 2933779. There's also a list of bugs fixed for this release.
VS 2013 Update 3 includes a new version of the C++ compiler (18.00.30723.0). There's no new C/C++ Runtime--it still uses CRT version 12.0.21005.1 from VS 2013 RTM), but there are updated remote debugging tools packages.
Windows SDK: VS 2013 Update 3 includes the April 2014 refresh of the Windows 8.1 SDK for the Windows 8.1 Update.
Windows phone: The Windows Phone 8.1 Update emulators are now also available for download.
VS Graphics Diagnostics: See this article for details. See also KB 2955817.
Improved optimized debugging: The /Zo switch is now officially supported. See Bruce Dawson's blog for the gory details.
Related: Visual Studio 2013 RTM, VS 2013 Update 1, VS 2013 Update 2