> No, you don't. Without training cost you can infer only the marginal cost of serving this kind of models.

Still useful; "are the labs marginally profitable just on the marginal inference costs?" is still a useful question to answer. After all, if they aren't even profitable on inference in isolation, then we can expect to see large price increases.

If they are able to turn a marginal profit on inference alone, then perhaps the price increases won't be so severe (or perhaps they expand the time between generations so that they spend less on training but take longer to complete training).

"Are the labs profitable at all?" is, of course, a much more useful question, but that doesn't mean that the first question is completely useless.