You will be billed for your OpenAI API usage at the end of each calendar month, unless you have a different, custom billing arrangement in writing.
Understanding API Billing and Invoicing
OpenAI provides invoices only for customers on Enterprise plans.
If you are an Enterprise API customer:
You are billed at the end of each calendar month for your usage during that month.
Invoices are typically issued within two weeks after the billing cycle ends.
Payment terms are determined by your Enterprise contract.
You can download invoices by visiting the Billing section of the OpenAI Platform.
Billing for Other Customer Types
If you are using the API as an Individual or Team customer:
You will not receive invoices.
Payment is handled via prepaid credits or automatically billed to your credit card.
You can view your payment history and receipts in the Billing section of your account.
These users pay either immediately at usage thresholds or monthly, depending on payment method and country.
For additional information on Prepaid billing, please refer to our help article: How can I set up prepaid billing?