The current plans for the Future Circular Collider are for it to be about 90 km in circumference, over 3 times longer than the current world champion, the Large Hadron Collider (LHC). That will give us collision energies of 100 TeV versus the LHC’s 14 TeV.
That is all well and good, but it could be a lot of work and $20 billion for nothing given that we have no compelling theoretical reasons to expect there to be anything new at those energies. Certainly, it would nail down a lot of details in the Standard Model of particle physics, but it might fall short of what is needed.