CAAD3 frames showed up first on mountain bikes in 1996. The key to it was a very large, thin down tube. At the crank it was shaped into the "power pyramid" which made the bb very stiff, and at the head tube it was tapered down to the right diameter to blend in. The 1997 road bikes got that, skinny seat tubes, and a carbon fork. The other two tubes were butted. CAAD4 in 1999 brought thinner chain stays, shaped seat stays. At the same time they were making cool house brand components like the Hollowgram cranks. The frames kept improving from there as the aluminum got better and the design got tweaks. This probably kept them out of the carbon frame business for another couple generations of bikes.

At the same time they were bankrupting themselves trying to make motorcycles.