When you use the API, all payment methods are pay-as-you-go and prepaid.
Both apply at the same time, meaning they are not mutually exclusive.
Let’s go over this with an example from OP and another one.
For GPT-4 (which probably refers to GPT-4 Turbo), the cost is $30 per 1M tokens.
GPT-4o and GPT-4-mini are different models with separate pricing.
Right now, only the prepaid method is accepted, but even with that, the price stays the same.
And prepaid credits stay valid for one year after purchase.
But you might wonder whether older credits get used first—I find this a bit confusing myself.
So, if you’re worried about that, you can either wait until your balance is low before recharging. Then, if your balance goes negative and auto-recharge is off, you will need to manually recharge to continue using the service. (I’m not entirely sure, but I believe that’s how it works.)
This might appear a bit off-topic, but:
Even if you turn on auto-recharge, you can still set a monthly spending limit using Budget Alert and Budget Limit.
When your spending hits the Budget Alert amount, you’ll get an email notification.
And when you reach the Budget Limit, your usage for that month will be paused.
But please keep in mind, there’s a delay in detecting when you go over the Budget Limit, so you might still be charged beyond it, and in some cases, the excess could be substantial depending on usage speed.
This feature helps keep spending under control, but it’s not a hard limit.
If you want strict control over your spending, perhaps the best approach is to turn off auto-recharge and only use the amount you’ve prepaid.
I hope this helps!