Supposedly they will eventually have a larger pack than what is currently available, i.e. the large pack. I know you cannot currently configure an R1S with a max pack. I don't know if the biggest pack will be as big as the max pack was supposed to be, 180kwh, but they are going to have something bigger than the 135kwh.
In my case a bigger pack than 135kwh is absolutely critical. My wife and I go to Mammoth just about every other weekend in the winter from Newport Beach. For the last two winters we have done so in a Tesla Model 3 AWD long range. While the listed range for the Tesla is only 322 miles, it gets that range on 75kwh of battery. This means that while the range is not huge, you can add range quickly while charging. In practice I have found that driving the Tesla adds about 15-20 minutes to the drive to Mammoth, which I can live with. Adding that much time to a 340 mile drive is something I can live with.
The issue with the RIvian large pack would be that while the range might be comparable to my Tesla, it takes a HUGE pack to generate that range, 135kwh. Thus, it would take a very long time to add miles by charging on the road. For a vehicle as large as an R1S or an R1T or a Cybertruck I would need a big range. According to A Better Route Planner, and they will admit that this is speculative at this point due to no real world data, I could get to Mammoth from my house with only 28 minutes of charging in a max pack R1S or R1T. The Cybertruck would take only 17 minutes. These are all numbers I can live with. The 135 kwh pack R1S would take 42 minutes. Obviously these number vary, but because of the distance to Mammoth, and because we go so often, a large battery pack is critical for me in a large car.
The Fisker would seem to be a good compromise. The 350 mile range is more than the model 3 I currently drive, and while it won't add mileage quite as quickly the added range will probably make things a wash. Also, I really like the size of the Ocean. I like an SUV that is a bit smaller. I surf quite a bit and I'm often parallel parking near the beach in Newport or Huntington.
Sorry for the long winded explanation on my range needs.
But yeah, I don't think you can currently configure a max pack R1S. The word is that there will be a bigger pack one coming, but I don't think those details have been released yet. I have heard that they had issues with having enough space for the 180kwh pack, but I don't know that for a fact, just things I have heard in the Rivian forums. A bigger pack R1S should eventually be coming, but just how big that will be I certainly don't know.