A scintillating bolometer based on a large cubic Li2100MoO4 crystal (45 mm side) and a Ge wafer (scintillation detector) has been operated in the CROSS cryogenic facility at the Canfranc underground laboratory in Spain. The dual-readout detector is a prototype of the technology that will be used in the next-generation 0ν2β experiment CUPID . The measurements were performed at 18 and 12 mK temperature in a pulse tube dilution refrigerator. This setup utilizes the same technology as the CUORE cryostat that will host CUPID and so represents an accurate estimation of the expected performance. The Li2100MoO4 bolometer shows a high energy resolution of 6 keV FWHM at the 2615 keV γ line. The detection of scintillation light for each event triggered by the Li2100MoO4 bolometer allowed for a full separation (∼8σ) between γ(β) and α events above 2 MeV . The Li2100MoO4 crystal also shows a high internal radiopurity with 228Th and 226Ra activities of less than 3 and 8 μBq/kg, respectively. Taking also into account the advantage of a more compact and massive detector array, which can be made of cubic-shaped crystals (compared to the cylindrical ones), this test demonstrates the great potential of cubic Li2100MoO4 scintillating bolometers for high-sensitivity searches for the 100Mo 0ν2β decay in CROSS and CUPID projects.