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Codex CLI Integration

Use any model with OpenAI's Codex CLI through LLM Gateway. One config file, full cost tracking.

Codex CLI is OpenAI's open-source terminal coding agent. By default it connects to OpenAI's API, but with LLM Gateway you can route it through a single gateway—use GPT-5.3 Codex, Gemini, Claude, or any of 180+ models while keeping full cost visibility.

One config file. No code changes. Full cost tracking in your dashboard.

Quick Start

1. Log out of ChatGPT if you're logged in (stored sessions override custom config):

1codex logout

2. Create or edit your Codex CLI config file at ~/.codex/config.toml:

1model = "auto"
2model_reasoning_effort = "high"
3openai_base_url = "https://api.llmgateway.io/v1"

3. Run Codex CLI:

1codex

On first launch, Codex will prompt you for authentication. Select Provide your own API key, then enter your LLM Gateway API key (starts with llmgtwy_).

Why This Works

LLM Gateway's /v1 endpoint is fully OpenAI-compatible. Codex CLI sends requests to our gateway instead of OpenAI directly, and we route them to the right provider behind the scenes. This means:

  • Use any model — GPT-5.3 Codex, Gemini, Claude, or 180+ others
  • Keep your workflow — Codex CLI doesn't know the difference
  • Track costs — Every request appears in your LLM Gateway dashboard
  • Automatic caching — Repeated requests hit cache, saving money

Configuration Explained

Base URL

The openai_base_url field points Codex CLI to LLM Gateway instead of OpenAI:

1openai_base_url = "https://api.llmgateway.io/v1"

Model Selection

Use auto to let LLM Gateway pick the best model, or set a specific one from the models page:

1model = "auto"
2# or pick a specific model
3model = "gpt-5.3-codex"

Reasoning Effort

Control how much reasoning the model uses. Options are low, medium, and high:

1model_reasoning_effort = "high"

Choosing Models

Use auto to let LLM Gateway pick the best model automatically, or choose a specific one from the models page:

1# let LLM Gateway pick the best model
2model = "auto"
3

4# or pick a specific model
5model = "gpt-5.3-codex"

What You Get

  • Any model in Codex CLI — GPT-5.3 Codex for heavy lifting, lighter models for routine tasks
  • Cost visibility — See exactly what each coding session costs
  • One bill — Stop managing separate accounts for OpenAI, Anthropic, Google
  • Response caching — Repeated requests hit cache automatically
  • Discounts — Check discounted models for savings up to 90%

Troubleshooting

Data retention required

If you see an error like:

1The Responses API requires data retention to be enabled.

Codex CLI uses the OpenAI Responses API (/v1/responses), which requires data retention to be enabled. To fix this:

  1. Go to your organization settings and navigate to Settings > Policies
  2. Select Retain All Data and click Save Settings

If you prefer not to enable data retention, you can configure Codex CLI to use the Chat Completions API instead by setting the OPENAI_CHAT_COMPLETIONS_PATH environment variable, if supported by your Codex CLI version.

Authentication errors

If you see 401 Unauthorized or requests going to api.openai.com instead of LLM Gateway:

  1. Make sure you've run codex logout to clear any ChatGPT session
  2. Verify openai_base_url is set in ~/.codex/config.toml
  3. When Codex prompts for authentication, select Provide your own API key and enter your LLM Gateway key (starts with llmgtwy_)

Model not found

Verify the model ID matches exactly what's listed on the models page. Model IDs are case-sensitive.

Connection issues

Check that openai_base_url is set to https://api.llmgateway.io/v1 (note the /v1 at the end).

Get Started

  1. Sign up free — no credit card required
  2. Copy your API key from the dashboard
  3. Run codex logout to clear any existing ChatGPT session
  4. Create the config file above
  5. Run codex, select Provide your own API key when prompted, and paste your LLM Gateway key

Questions? Check our docs or join Discord.