Stacked devices and methods of fabrication are provided. Die-to-wafer (D2W) direct-bonding techniques join layers of dies of various physical sizes, form factors, and foundry nodes to a semiconductor wafer, to interposers, or to boards and panels, allowing mixing and matching of variegated dies in the fabrication of 3D stacked devices during wafer level packaging (WLP). Molding material fills in lateral spaces between dies to enable fan-out versions of 3D die stacks with fine pitch leads and capability of vertical through-vias throughout. Molding material is planarized to create direct-bonding surfaces between multiple layers of the variegated dies for high interconnect density and reduction of vertical height. Interposers with variegated dies on one or both sides can be created and bonded to wafers.