> Inference costs scale linearly with usage. R&D expenses do not.

Do we know this is true for AI?

It’s pretty much the definition of fixed costs versus variable costs.

You spend the same amount on R&D whether you have one hobbyist user or 90% market share.

Yes. R&D is guaranteed to fall as a percentage of costs eventually. The only question is when, and there is also a question of who is still solvent when that time comes. It is competition and an innovation race that keeps it so high, and it won't stay so high forever. Either rising revenues or falling competition will bring R&D costs down as a percentage of revenue at some point.

Yes, but eventually may be longer than the market can hold out. So far R&D expenses have skyrocketed and it does not look like that will be changing anytime soon.

That's why it is a bet, and not a sure thing.