Codex is OpenAI's coding agent. You can use it inside the ChatGPT desktop app or from the terminal with Codex CLI. Both local clients use the same user-level ~/.codex/config.toml, so you only need to configure CrossModel once.

CrossModel supports the Responses API used by Codex directly. You do not need to install or run a separate router or proxy.

Quickstart

1. Choose a client

For the desktop experience, install the ChatGPT desktop app, sign in, and choose Codex.

If you also want the terminal client, install Codex CLI.

macOS / Linux:

curl -fsSL https://chatgpt.com/codex/install.sh | sh

Windows:

powershell -ExecutionPolicy ByPass -c "irm https://chatgpt.com/codex/install.ps1 | iex"

Or install it with npm:

npm install -g @openai/codex

Already using either client? Skip the installation and continue with the same configuration below.

2. Create an API key

Sign in to the Console and create a key that starts with cm- on the API Keys page. The key is shown only once, so copy it somewhere safe.

3. Add CrossModel as the shared provider

Edit ~/.codex/config.toml and add the following configuration. Create the file if it does not exist.

model_provider = "crossmodel"
model = "deepseek/deepseek-v4-pro"
 
[model_providers.crossmodel]
name = "CrossModel"
base_url = "https://api.crossmodel.ai/v1"
env_key = "CROSSMODEL_API_KEY"
wire_api = "responses"

This is a user-level setting shared by the ChatGPT desktop app's Codex workspace and Codex CLI. The provider block follows OpenAI's custom model provider configuration: base_url points Codex at CrossModel, env_key names the environment variable that contains your key, and wire_api selects the Responses API.

4. Set the API key environment variable

On macOS or Linux, add the variable to your shell profile (~/.zshrc or ~/.bashrc):

export CROSSMODEL_API_KEY="cm-YOUR_KEY"

Open a new terminal, or reload the profile you edited:

source ~/.zshrc

On Windows PowerShell, set it for the current session:

$env:CROSSMODEL_API_KEY = "cm-YOUR_KEY"

To save it as a user environment variable for future PowerShell sessions and the desktop app:

[Environment]::SetEnvironmentVariable("CROSSMODEL_API_KEY", "cm-YOUR_KEY", "User")

5. Start Codex

In the ChatGPT desktop app, choose Codex, open your project, and start a new task. After changing config.toml, fully quit and reopen ChatGPT before testing.

For Codex CLI, run it from your project directory:

cd /path/to/your/project
codex

How it works

Codex sends Responses API requests directly to https://api.crossmodel.ai/v1. CrossModel authenticates the cm- key, routes each request to the selected upstream model, converts protocols when necessary, and bills usage to your CrossModel wallet. There is no local routing service to install or keep running.

Choosing models

Change the default model by editing the model field in ~/.codex/config.toml. This guide deliberately uses deepseek/deepseek-v4-pro to show that Codex can run with a non-OpenAI model through CrossModel. Model IDs use the vendor/short_name format; browse the current IDs and capabilities in the model catalog.

For a one-off CLI session, override the configured model with -m:

codex -m openai/gpt-5.6-terra

Choose a model with tool-calling support for the full agent experience. The built-in model picker may not discover every model in the CrossModel catalog automatically; setting model explicitly still works.

Troubleshooting

Official references

• ChatGPT desktop app
• Codex CLI
• Custom model providers
• Codex environment variables