I'd be shocked if the range extender was attached at the factory. It seems to me that the whole reason they did the range extender was to keep the price/cost down for the base models and still qualify for the tax credit.If range extender is a physically attached factory option you'd no longer qualify for the tax credit as those count toward the cap- as things like wheels and paint do now.
SOFTWARE options (or post-delivery add ons) do not.
Most won't need the range extender, but at least Tesla can offer it and say they have a truck with a longer range than Rivian.