Do you have to pay for GPT?

Excuse me, could you clarify something for me? In regards to the topic of GPT, I'm a bit confused. Is there a cost associated with using GPT? Do users need to pay for its services? I'm just trying to get a better understanding of the financial aspect of this technology. If there is a fee, how is it structured? Is it a one-time payment, a subscription-based model, or something else entirely? I'd appreciate any insight you can provide.