Xsun was first released as part of Solaris 2.3 in November 1993. It was originally based on X11 Release 5; the version included with Solaris 10 is based on X11R6.6.
Solaris 10 includes both Xsun and the X.Org Server, the open-source softwarereference implementation of X, based on X11R7. The "Xorg" server is the most commonly used server for x86 systems, and the Xsun server remains the most commonly used for SPARC systems; Xorg support for SPARC was only added in Solaris 10 8/07, and has very limited driver support. The OpenSolaris project has stated that the future direction for X support is via the Xorg implementation. Oracle Solaris 11, released in November, 2011, includes only Xorg implementation of X11 server (X.org 1.10.3); therefore, Xsun implementation has been deprecated. 
^"OpenSolaris Community: X Window System". Retrieved 2008-07-23. Over time we are working to migrate the existing libraries and clients to build from the newer source base as well for future Solaris releases.