Is Carbon the next version of Argon? My understanding was that Argon is the middle-tier model (somewhere between OpenAI's Terra and Sol in position) whereas Carbon is supposed to be like Astra. This is assuming they don't have an even higher tier model upcoming, in which case Argon ~ Terra, Carbon ~ Sol and Element X (Plutonium?) ~ Astra.

Wild guess: maybe they are going with how abundant the elements are to scale the models. I'm no chemist so I don't know reliably how the relative abundance of Argon and Carbon works out, but Hydrogen is "well-known" as the most abundant element in the universe, so maybe that's why its the base model. But, this is essentially a trend of one, so not a trend at all, unless someone can verify it still works for Argon and Carbon.