Through different annealing temperatures and times, it is reported here that interstitial metastable high entropy alloys (HEAs) can exhibit a wide range of strength-ductility trade-offs. The underlying mechanisms were investigated via in situ neutron diffraction, electron backscattered diffraction, and electron channel contrast imaging analyses. These techniques revealed that the phase transformation process could be tuned by various annealing processes, resulting in different degrees of load partitioning and sharing among different phases and grain families on the commensurate microstructural length scales. Therefore, the microstructures generated by thermal treatments and phase transformation from face-centered-cubic to hexagonal-close-packed phases could efficiently improve the ductility of the studied alloys.