I’m not entirely ruling out the possibility that I might be missing something.
However, to the best of my knowledge, OpenAI is the only LLM service provider that insists on a prepaid system. Take Microsoft Azure for instance, it doesn’t employ a prepaid system at all, and if you hold a Microsoft Azure account, it operates on a monthly billing basis.
This might just be my case, but both Anthropic and Mistral also operate on a monthly billing system.
I don’t believe the current tier system holds any significance.