I also wonder if this means that even paid tiers will get ads. Google's ad revenue is only ~$30 per user per year, yet there is no paid, ad-free Google Premium, even though lots of users would gladly pay way more than $30/year have an ad-free experience. There's no Google Premium because Google's ad revenue isn't uniformly distributed across users; it's heavily skewed towards the wealthiest users, exactly the users most likely to purchase an ad-free experience. In order to recoup the lost ad revenue from those wealthy users, Google would have to charge something exorbitant, which nobody would be willing to pay.
I fear the same will happen with chatbots. The users paying $20 or $200/month for premium tiers of ChatGPT are precisely the ones you don't want to exclude from generating ad revenue.