Account or API key, again
Codex, like the Claude CLI, gives you two ways to sign in, and the choice is the same one you already learned.
ChatGPT account (what you just did)
You, a human, at your own machine. You sign in through the browser with your ChatGPT account, and your existing plan covers normal interactive use. This is your path for everything in this course. If a person is sitting at the terminal, this is the answer.
API key
Codex also accepts an API key, a single long secret string that
stands in for the browser sign-in. With Codex, you'd typically set it
as a value called OPENAI_API_KEY.
It's the same story as the Claude CLI's API key. The key is for situations with no human present to click anything: a program on a server, an automated job in a pipeline, a tool calling Codex on its own. It also bills differently, by usage against a developer account, which suits unattended jobs and not a person learning at a terminal.
The rule, unchanged
Human at the keyboard, use the account sign-in. Program running unattended, that's when an API key earns its place. You're a human at the keyboard. The account sign-in you just did is correct.
This is the second time you've seen this exact choice, once per tool.
That's the point of seeing it twice: "account for humans, API key for
unattended programs" is not a Claude rule or an OpenAI rule. It's how
these tools work in general. Chapter 18 covers handling keys like
OPENAI_API_KEY safely once you reach automated jobs.
Account or API key, again
Codex, like the Claude CLI, gives you two ways to sign in, and the choice is the same one you already learned.
ChatGPT account (what you just did)
You, a human, at your own machine. You sign in through the browser with your ChatGPT account, and your existing plan covers normal interactive use. This is your path for everything in this course. If a person is sitting at the terminal, this is the answer.
API key
Codex also accepts an API key, a single long secret string that
stands in for the browser sign-in. With Codex, you'd typically set it
as a value called OPENAI_API_KEY.
It's the same story as the Claude CLI's API key. The key is for situations with no human present to click anything: a program on a server, an automated job in a pipeline, a tool calling Codex on its own. It also bills differently, by usage against a developer account, which suits unattended jobs and not a person learning at a terminal.
The rule, unchanged
Human at the keyboard, use the account sign-in. Program running unattended, that's when an API key earns its place. You're a human at the keyboard. The account sign-in you just did is correct.
This is the second time you've seen this exact choice, once per tool.
That's the point of seeing it twice: "account for humans, API key for
unattended programs" is not a Claude rule or an OpenAI rule. It's how
these tools work in general. Chapter 18 covers handling keys like
OPENAI_API_KEY safely once you reach automated jobs.