In the tubular tire-rim interface, the difficult surface to work with is the rim. Base tape, which is just about always a woven strip of cotton cloth, is easy. Glue seeps between the threads, stays there, and dries. The rim is another story. The glue has to bond to the rim in some way, but not permanently. Conventional wisdom is that conventional tubular glue takes a bit more care in prep when mounting tubulars to carbon rims.
Enter the Continental Carbon-Specific tubular glue. It is formulated specifically for use on carbon. Unfortunately, they won't tell us the science behind what makes it carbon-specific. All they're saying is their carbon-rim glue is optimized for carbon. Conti's standard glue is optimized for aluminum. All the same, Continental says either will work on either rim, just the specific glues work better with their intended rims. They also tell us that in terms of texture, viscosity, curing time, etc, the two glues are about the same.
A single 25g tube of Continental Carbon Rim glue should be enough to do one tire to one wheel, with maybe a little left over.