CDT 5.0.x (Ganymede)
CDT 5.0 will be released in June 2008. The CDT 5.0 plan is here
CDT 4.0.x (Europa)
CDT 4.0 was released in June 2007. It's plan is here.
CDT 4.0.x will be released along with the other Europa projects in the Fall Maintenance and Spring Maintenance releases. As well as in November 2007.
CDT 4.0.1 was released in September 2007. CDT 4.0.1 plan is here.
CDT 3.1.x (Callisto)
There are no further releases of 3.1.x (i.e. a 3.1.3) planned at this time. There have been a couple of patches applied to the CDT 3.1.x branch (cdt_3_1) after the 3.1.2 build that you may want to pick up. These builds are available on our built page at http://download.eclipse.org/tools/cdt/builds/3.1.2/index.html.