  We use effective kinetic theory to study the pre-equilibrium dynamics in
heavy-ion collisions. We describe the evolution of linearized energy
perturbations on top of out-of-equilibrium background to the energy-momentum
tensor at a time when hydrodynamics becomes applicable. We apply this
description to IP-Glasma initial conditions and find an overall smooth
transition to hydrodynamics. In a phenomenologically favorable range of
$\eta/s$ values, early time dynamics can be accurately described in terms of a
few functions of a scaled time variable $\tau T/(\eta/s)$. Our framework can be
readily applied to other initial state models to provide the pre-equilibrium
dynamics of the energy momentum tensor.
