I will introduce the (3+1)D dilute Glasma approximation, a semi-analytic framework for the computation of rapidity-dependent early-time observables in relativistic heavy-ion collisions. Starting from the Color Glass Condensate effective field theory, we describe the gluonic interaction between the large Bjorken-x, static sources localized in the colliding partners by classical Yang-Mills equations. We then linearize the Yang-Mills equations assuming weak sources and obtain remarkably simple, analytic solutions for the Glasma field strength tensor. I will present our results for Pb+Pb collisions at LHC and Au+Au collisions at RHIC energies using a generalized McLerran-Venugopalan nuclear model with parametrized longitudinal correlations. In particular, we find limiting fragmentation on the level of the energy-momentum tensor up to LHC energies as a universal feature of our model.