Within the GMT technology project (Generative Modeling Tools), an initial set of tools and artifacts for Global Model Management have recently been released under Eclipse. This paper presents the corresponding AM3 (ATLAS MegaModel Management) goals and contributions. AM3 is intended to provide support for modeling in the large, i.e. managing global resources in the field of MDE (Model-Driven Engineering). These global resources are usually heterogeneous and distributed. To access them without increasing the accidental complexity of MDE, we need to invent new ways to create, store, view, access, and modify the global entities that may be involved in developing a solution. To this intent, the notion of a megamodel (i.e. a model which elements are themselves models) is being used. This paper reports on the goals, the present state, and some future planned evolution of this Eclipse contribution.