[en] Design version of a 400-400 GeV² Isabelle proton-proton colliding beam facility is described. The higher energy capability is achieved by increasing the total bending length and increasing the peak magnetic field design value to 5T. The design luminosity at maximum energy is 2x10³² cm^-2s^-1 for a ''standard insertion setup, increasing to 10³³ cm^-2s^-1 for a high luminosity configuration. The dominant performance limitations are considered. It is shown that performance limitations due to high intensity effects are no more severe than in the 200 GeV design. At energies <= 200 GeV the luminosity value is at worst a factor of √ 2 lower than that of the 200 GeV design. The cost increase of the 4O0 GeV version by approximately 40% is over that of the basic 200 GeV design (173 million pounds) and works out