Technically, any window AC — and any air conditioner — is a heat pump. But usually when folks use the term ‘heat pump’ in the HVAC industry, they're referring to an AC that can also provide heating. That’s what the Gradient offers; it'll cool your home in warm weather, and then switch to heat in the winter.
We are starting to see window ACs that also provide heating. Some of those units use heat pump technology, but some of them only use a resistance heater — a much less efficient approach. Both of these systems see limited adoption because they're fairly limited in capacity and efficiency.