To identify which model your OpenAI API key is associated with, you will need to check your usage through OpenAI’s platform. When you access the API, you specify the model you want to use (like GPT-4, GPT-3.5, or others) in the API request. If you’re unsure about the model, you can visit your API dashboard where it will show which models you’ve used and the corresponding usage data.
Here are some links that may help.
Regarding testing the API without payment, OpenAI used to offer free credits (around $18) for new accounts, which could be used to explore the API. However, this program has been discontinued for most users unless you are part of a specific promotional program. Now, to test the API, you will need to add payment details and purchase at least $5 worth of credits. This allows for a “pay-as-you-go” system, so you only pay for what you use.
You can test basic features of OpenAI’s models without writing your own API code using the OpenAI Playground. This is a no-code environment where you can experiment with models like GPT-4, GPT-3.5, and others.
https://platform.openai.com/playground/chat
This is old but still useful for past reference.
https://openai.com/index/openai-api/