As 3D-printed concrete (3DPC) advances toward structural-scale applications, the performance of interlayer interfaces remains a critical challenge. This work investigates the shear behavior of both horizontal and vertical joints in 3DPC through a series of customized push-off tests. A novel triplet specimen configuration was developed to evaluate horizontal interfaces between printed layers, incorporating both monolithically cast and 3D-printed specimens. In parallel, S-shaped specimens were used to simulate vertical joints between, e.g., 3D-printed layers printed in parallel. The experimental campaign assessed nominal interfacial shear strength, crack development, and failure modes. Crack propagation and peak stress behavior were used to characterize interfacial integrity across configurations. For the horizontal joints, 3D-printed triplet specimens achieved an average shear stress of 7.8 MPa, representing approximately 52% of the strength of the monolithically cast references (14.9 MPa). In contrast, S-shaped specimens—representing vertical interfaces—reached an average of 2.9 MPa, corresponding to only 19% of the cast reference and 37% of the 3D-printed triplets. All S-shaped specimens failed through diagonal interlayer cracking, confirming the anisotropic behavior of 3D-printed concrete and highlighting the challenges of shear transfer in vertically layered segments. These findings emphasize the importance of interface orientation and construction sequence. The proposed test configurations provide a robust framework for evaluating interlayer performance and demonstrate how process tuning can improve the structural reliability of modular 3D-printed systems.