Lightweight climbing bike

So, I’ve recently bought a Tri bike, Cannondale Slice, an aero road bike, Scott Foil, and I’d really like to buy a lightweight climbing bike.
I’ve got a 15yo Cervelo R3, really lovely bike, but I’m curious as to what 's out there now that would be better.
What’s out there now that would be an improvement on the R3?
Be good to know of riders first hand experiences of riding a newer lightweight, stiff, climbing bike.

Many thanks

I haven’t ridden R3 but had an R5 before my current bike Canyon SLX Ultimate. Biggest diffrents for me was the comfort I ride alot in the alps in the summer an roads are often bad.
I still have same groupset and wheels as my old bike. How much the comfort depends on bigger tire size can I not say since I went up from 25c to 28c (now 32c) when I got the new frame.
I would say a new TL wheelsset can probally be a better first step upgrade if you don’t have.