How to use my own API key for OpenAI 4.5 model?

Questions
1

How can I set up my own API for OpenAI 4.5? I have read this article, but it seems outdated:Why should I use an OpenAI API key in a Pickaxe?

2

Hi,

This post goes over that the API key settings are now in the settings tab. As far as why to use one, it remains because once your API key is connected, we don’t charge you for usage any further.

3

Thank you. Does this mean that, even with your own API, you cannot use all models without PRO? I cannot select 4.5, for instance.

4

Yes, that is correct