Judging by the leaks, OpenAI and Anthropic already train reasoning traces to use fewer tokens (they deliberately omit articles and prepositions, use very short sentences, etc.), even though you pay per token. So it wouldn't make sense to do that if the only incentive was "make them pay for as many tokens as possible per task."

It's more subtle than that. If a user has to wait longer for a solution/pay more, they'll be less satisfied and may switch to a competitor. More unnecessary tokens also means more unnecessary compute. Longer sessions are increasingly more expensive to serve than shorter sessions.

And there's always the Jevons effect: as a resource becomes cheaper, demand often increases, and so does net resource consumption.

So, imho, frontier labs have every incentive to reduce token usage per task (while also making you use AI for more and more tasks in your daily life)