We employ the leading order QCD kinetic theory to describe a consistent matching between

the initial stage of a heavy ion collision and the subsequent hydrodynamic evolution. We use

the linearized kinetic response functions around the non-equilibirum longitudinally expanding

background to map initial energy and momentum perturbations to the energy momentum tensor

at hydrodynamic initialization time τ hydro . We check that hadronic observables then become

rather insensitive to the cross-over time between kinetic theory and viscous hydrodynamics. The

universal scaling of kinetic response in units of kinetic relaxation time allows for a

straightforward application of kinetic pre-equilibration event-by-event.