What
An API key is the secret code that lets Claude Code use an account. When Claude Code finds one in your environment, it shows a dialog that begins "Detected a custom API key in your environment". Pressing Ctrl+C or Ctrl+D while that dialog is showing now exits.
Why
You can leave the dialog with the usual quit keys without having to answer it first.
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubt
Whether Ctrl+C or Ctrl+D closes only the dialog or quits Claude Code altogether is not shown.