There's a difference between model training and model fine tuning. Model training is not something e.g. OpenAI does a lot. The cutoff for gpt 5 was actually quite long a go. They sat on that for almost a year while they fine tuned the model. Finetuning is a lot faster and cheaper than training the full model. Training + finetuning is essentially fixed cost.

And you have to see this in proportion to the revenue. If you charge 20$/month and you have a few tens of millions of paying users and some premium tier users, that generates quite a bit of revenue.

OpenAI recently claimed they have 700 million regular users. I'm not sure how real/accurate that number is, but if one tenth of those pay for it it, that would be 1.4 billion per month coming in. That's excluding higher tiers. And I suspect they are shooting for a much larger market and are going to be nudging people to a bit higher tiers. Some have suggested that employers paying hundreds of dollars per month for AI subscriptions per employee might become normal in some sectors. That's an awful lot of money and I don't think they are done growing.

And of course with that kind of revenue, you can burn some cash on training cost. A few hundred million is basically nothing.

OpenAI has raised tens of billions of money. But they should be making 10-20 billions of revenue per year as well with some healthy growth. And they are showing very little signs of running out of money.