Both are Graded Hammer. Yamaha makes several versions of the Graded Hammer action. They are certainly not the same in the CP4 Stage and CP40 Stage, quite different.

The CP4 Stage has NW (natural wood white keys) GH3 (Graded Hammer triple sensor) with Synthetic Ivorite keytops _ features the CFX Grand Piano and the S6 Grand (in addition to the CFIIIS 9ft. Grand). Split and Layer
The CP40 Stage has the Graded Hammer Effect action _ CFIIIS 9ft Grand; Split

Thanks very much. I assume that explains the small weight difference between the two and that the actions would play differently.

I have tried both the CP40 and the CP4 in my home for 30 days each time. The action is completely different. The CP40 feels more accurate when playing classical piano music that requires wide variations in dynamics. I think adding wooden keys to the CP4 was a mistake and more of a marketing ploy because it feels like I am pushing a wood piano key that has been cut in half with no hammer on the other end. It is very distracting does not allow me to suspend my disbelief that it is not a real piano. The CFX grand piano is not better than the CFIIIS. In fact, for classical music the CFIIIS sounds better. There are tuning issues in the lower register of the CFX samples as well as velocity and/or sampling issues with respect to D6 on the CFX sample. D6 will not play as loud as the surrounding notes which makes the response to my playing inaccurate making it sound like I am playing that note with less velocity than I really am. The S6 sample sounds thin and has tuning issues below C2. The other issue I found with the CP4 is the key spacing is uneven. Keys have different amounts of space between them. They are not uniform. I did not find this problem on the CP40. It's sad because I really wanted to like the CP4 more than the CP40 especially because of all the hype surrounding the action and the larger palette of sounds. the key travel on both instruments is shallow but that shorter key travel is something that has been in all Yamaha acoustic and digital pianos since the 90s. It would have been nice to have a Steinway D and Steinway B in addition to the CFX, CFIIIS and S6.