Hybrid mode
Hybrid mode is a heat pump water heater setting that combines the efficient heat pump with fast electric resistance elements: the heat pump does routine heating, and the elements jump in when demand outruns it.
Most HPWHs offer several modes — heat-pump-only (maximum efficiency, slowest recovery), hybrid (the default balance), and electric/boost (fastest, least efficient). The certified UEF is measured in the default mode.
Running in heat-pump-only mode maximizes savings but stretches recovery time to several hours for a large tank; hybrid mode is why a well-sized HPWH keeps up with a family of four without cold showers.