> The largest of these models are incredibly expensive. They’re expensive to make, with billions spent acquir­ing training data, labelling it, and running it through massive computing arrays to turn it into models.

This is the part that doesn't seem like an unsustainable bubble. Initial training is very expensive. The cost of running a trained model keeps coming down as we find more and more ways of making it smaller while maintaining a high level of accuracy. It really comes down to if these advancements can keep going and meet costs before investment dries up.