NeXus is a parton-based Gribov-Regge model which calculates macroscopic quantities like energy density or rapidity fields at an early stage of a nucleus-nucleus collision at ultrarelativistic energies. In this model, the hard partons are treated explicitly based on pQCD, while the soft ones are included implicitly, using the string picture.

NeXus provides the initial condition for the hydrodynamics, namely, the energy-momentum and other conserved charge distributions.