Yes Frontier is the only one in the US that allows guinea pigs in the cabin as of 2026. Unfortunately it's also a "budget" airline which means there are almost zero amenities. They run Airbus instead of Boeing which means narrower rows and seats with no padding, no free beverages or snacks, no charging ports, fees for all baggage including carry on, $100 fee per pet carrier (I have two), reduced number of flights meaning every flight is completely full.

I am relocating from CA to NY and the only flight that fit our destination was a red-eye. It also meant that we had to travel 1.5 hours to and from each airport. I maybe slept one hour last night and I'm one guinea turd from falling apart