The effect of aging in the high-temperature B2-phase on the martensitic transformation, the strength properties of L1₀-martensite, and the cyclic stability of superelasticity in compression in [001]B2-oriented Co35Ni35Al28Fe2 single crystals was investigated. The B2-phase in quenched Co35Ni35Al28Fe2 single crystals remains stable without precipitation of secondary phases upon heating up to 520 K, which represents an increase of approximately 50 K compared to ternary Co35Ni35Al30 alloys. Aging at 673 K leads to the precipitation of nanosized (Ni,Co)5Al3-particles providing dispersion strengthening. Short-term aging for 15 min decreases the start B2-L10 martensitic transformation temperature Ms by 140 K and significantly improves functional properties, resulting in a wide temperature range of superelasticity (345 K) and high strength properties of L10-martensite (> 1870 MPa) while maintaining cyclic stability of superelasticity.