My Champion 3500/4000 is several years old. When I bought it, the only difference between CARB-compliant and non-CARB was the spark arrestor in the tail pipe.
As said, the 12-hour rating is calculated on the 3500 watt output. In practice, this generator will not sustain the full 3500 for long periods at very high altitude, or very high heat, although it does fine for me in 100-degree heat at 3000 feet, and did fine at 9000 feet in mild weather.
This generator is a great choice for boondocking and running your Air conditioner. I am sorry that you've recieved so much hair-brained advice about camping with neighbors, or whether to run your A/C at all. This generator is louder (but more reliable) than an inverter generator costing five times as much, but quieter than virtually any generator in its price category, or even costing twice as much. It is well built, and very well supported by the company. You cannot go wrong buying this generator.