CCSDT and δ DLPNO-CCSD(T) DLPNO-CCSDT remain within 1 kJ mol -1 (0.24 kcal mol -1 ), we find that there is unfavorable error cancellation that occurs in most cases between DLPNO-CCSDT and DLPNO-CCSD(T). This is because the DLPNO-(T) energy is explicitly a function of the triples amplitude, while the DLPNO-CCSDT energy is only a functional of converged DLPNO-CCSDT singles and doubles amplitudes. This leads to a rank mismatch that yields unpredictable error cancellation. These issues are mitigated in cases of unimolecular reactions, denoted with (*) in Tables and. In these cases, δ DLPNO-CCSD(T) DLPNO-CCSDT approximates δ CCSD(T) CCSDT quite accurately due to the lack of the rank error induced by the differences in system size between reagents and products. This is congruent with the observation of Gray and Herbert, that rank corrections such as the counterpoise (CP) correction are helpful when computing energy differences involving systems of different sizes, when used in the context of DLPNO. We recommend that for approximating δ