1. Configure OpenAI keys

export OPENAI_API_KEY=$CBORG_API_KEY
export OPENAI_BASE_URL=https://api.cborg.lbl.gov

2. Restart shell and verify key settings

env | grep OPENAI

3. Start Codex

cd my-project
codex

Note: The default model is o4-mini.

The gpt-5-codex model is also supported and is recommended for best performance.

The model can be configured in a .codex file or passing the –model argument., e.g.

alias codex=codex -m gpt-5-codex

For more information see OpenAI Codex Github