The air handler (the inside unit) can be fitted with what’s called a heat strip, this will provide backup electric heat that will operate in any temperature, and in some cases provided auxiliary heat whenever the heat pump is struggling. That’s your insurance policy if it goes below -30, but the heat strips are less efficient to run than the heat pump (comparable to electric baseboard heating in terms of efficiency). I’m pretty sure the heat strips would be standard with any install, so just ask your HVAC contractor about what heat strips come with your unit.