GPT-4 is only available once you have used a sufficient amount of their APIs to owe OpenAI at least a dollar. After your first payment, they will make GPT-4 available to you.
On July 6, 2023, we gave access to the GPT-4 API (8k) to all API users who have made a successful payment of $1 or more.
If you have a newer account, simply purchase $0.50 of credits.
For API accounts created after August 18, 2023, you can get instant access to GPT-4 after purchasing $0.50 worth or more of pre-paid credits.