Using APIMart in Codex CLI

Introduction

Codex CLI is OpenAI’s open-source terminal coding agent that can read and write files, run commands, fix bugs, and complete full coding tasks directly in the command line. By connecting through APIMart, you can freely use multiple models — including GPT and Claude — in Codex CLI, with more flexible and competitive pricing.

Prerequisites

Before you begin, make sure you have:

Installed Node.js Download and install from the Node.js website (latest LTS, v20 or newer recommended) to install Codex CLI via npm
Obtained an APIMart API Key Log in to the APIMart Console to get your API key (starts with sk-)

Tip: If you don’t have an APIMart account yet, please register at APIMart first and obtain your API key.

Step 1: Install Codex CLI

Choose any of the following methods to install:

npm (Recommended)
Homebrew (macOS)

Install globally with npm — works on all operating systems:

npm install -g @openai/codex

If you run into permission issues, prepend sudo (macOS / Linux).

macOS users can also install with Homebrew:

brew install codex

Verify the installation

After installing, run the following command to confirm:

codex --version

If a version number is printed, the installation succeeded.

Step 2: Configure the APIMart API

Codex CLI manages model providers via configuration files under the ~/.codex/ directory. All we need to do is add a custom provider pointing to APIMart.

2.1 Locate the config directory

macOS / Linux: ~/.codex/
Windows: C:\Users\<username>\.codex\

If the directory does not exist, run codex once in your terminal then press Ctrl + C to exit — it will be created automatically.

2.2 Configure the API key

In the config directory, create or edit the auth.json file and fill in your APIMart key:

{
  "OPENAI_API_KEY": "sk-xxxxxxxxxxxx"
}

Field	Description
`OPENAI_API_KEY`	Your APIMart API key (starts with `sk-`)

2.3 Configure the model provider

In the config directory, create or edit the config.toml file and add the APIMart provider:

# Default model
model = "gpt-5.5"
# Default provider — matches [model_providers.apimart] below
model_provider = "apimart"

# APIMart provider configuration
[model_providers.apimart]
name = "APIMart"
base_url = "https://api.apimart.ai/v1"
wire_api = "responses"
requires_openai_auth = true

Field	Description
`model`	Default model ID — pick one from the model list below
`model_provider`	Default provider — must match the ID inside `[model_providers.xxx]`
`name`	Display name of the provider — can be customized
`base_url`	APIMart’s OpenAI-compatible URL — fixed at `https://api.apimart.ai/v1`
`wire_api`	Wire protocol — recent Codex versions require `responses` (Responses API)
`requires_openai_auth`	Set to `true` to authenticate using the key from `auth.json`

After saving both files, restart Codex CLI for the changes to take effect.

Make sure auth.json is valid JSON and config.toml is valid TOML. Do not use full-width / smart quotes, otherwise the config won’t apply.

Step 3: Get Started

Verify the configuration

In any project directory, run the following command to confirm everything is wired up:

codex "Introduce yourself in one sentence"

If you get an AI reply, the configuration is working. If you see a sign-in screen, or 401 / 403 errors, refer to the FAQ section below.

Interactive mode

Run codex directly to enter the interactive UI — ideal for full coding tasks:

codex

Once inside, describe what you need in natural language, e.g.:

Create an Express.js server with a JSON-returning health check endpoint

Codex will analyze your project, generate code, run commands, and ask for confirmation before performing sensitive operations.

Approval modes

On first run, Codex will ask you to pick an approval level:

Mode	Description
Read Only	Only file reads are allowed — any modification or command requires confirmation
Auto	Can read/write files and run commands within the working directory (recommended)
Full Access	Performs any operation without confirmation — use with caution

We recommend starting with Auto mode. Type /approvals in the interactive UI to change it anytime.

Switch models

In the interactive UI, type /model to switch quickly, or change the model field in config.toml and restart.

Supported Models

For Codex CLI, the following GPT-5 series models are recommended:

Model ID	Strengths	Recommended Use Cases
`gpt-5.5`	Latest flagship, top coding ability	First pick for Codex, complex engineering
`gpt-5.4`	Previous-generation flagship, very capable	Complex coding, architecture design
`gpt-5.4-mini`	Lightweight, fast, cost-effective	Daily coding, fast iteration
`gpt-5.3-codex`	Coding model optimized for Codex	Agentic coding tasks
`gpt-5.2`	Stable and balanced	Routine coding tasks

Model selection tips: The GPT-5 series above pairs best with Codex CLI. For the best experience, prefer gpt-5.5; gpt-5.3-codex is specifically optimized for Codex’s agentic coding scenarios.

Common Commands

Frequently used commands and shortcuts in Codex CLI:

Command	Description
`codex`	Enter the interactive UI
`codex "task"`	Start with an initial instruction
`codex exec "task"`	Non-interactive mode — run and exit
`codex --model gpt-5.4`	Start with a specified model
`codex --version`	Show the version number
`/model`	Switch model inside the interactive UI
`/approvals`	Adjust approval mode inside the UI
`Ctrl + C`	Exit the interactive UI

FAQ

If you see “Sign in with ChatGPT” or similar after launch, the configuration didn’t take effect. Troubleshooting:

Make sure both config.toml and auth.json are inside ~/.codex/
Check that model_provider in config.toml is set to apimart
Check that auth.json is valid JSON and the key is filled in completely

Q2: Getting 401 / 403 errors?

Status Code	Meaning	Solution
`401 Unauthorized`	Missing or invalid API key	Check the key in `auth.json` — it should start with `sk-`
`403 Forbidden`	Insufficient permission or expired key	Go to the Console to verify the key

Also make sure base_url is set to https://api.apimart.ai/v1, not the official OpenAI URL.

Q3: Connection failed?

Check your network connection
Make sure base_url in config.toml is correct
If you’re behind a proxy, ensure it allows access to api.apimart.ai

Q4: `wire_api = "chat"` is no longer supported?

Recent Codex CLI versions (0.84.0 and later) have removed the chat protocol. Update wire_api in config.toml to responses:

wire_api = "responses"

APIMart supports the Responses API — just restart Codex after the change.

Q5: Tool calls or runs are failing?

Make sure wire_api in config.toml is set to responses. If you still hit compatibility issues, switch to a recommended GPT-5 series model (e.g. gpt-5.5, gpt-5.3-codex) — they pair more reliably with Codex CLI.

Q6: Use environment variables instead of auth.json?

You can also configure the key via an environment variable. Change the provider block in config.toml to:

[model_providers.apimart]
name = "APIMart"
base_url = "https://api.apimart.ai/v1"
wire_api = "responses"
env_key = "APIMART_API_KEY"

Then set the environment variable APIMART_API_KEY to your APIMart key. auth.json is no longer required in this setup.

Q7: How do I switch models?

Two ways:

In the interactive UI: Type /model to switch
Edit the config: Change the model field in config.toml and restart Codex CLI

Q8: How do I check usage and billing?

Support and Help

If you run into any issues while using Codex CLI:

Chat Applications

Development Tools

Application Platforms

Using APIMart in Codex CLI

Introduction

Prerequisites

Step 1: Install Codex CLI

Verify the installation

Step 2: Configure the APIMart API

2.1 Locate the config directory

2.2 Configure the API key

2.3 Configure the model provider

Step 3: Get Started

Verify the configuration

Interactive mode

Approval modes

Switch models

Supported Models

Common Commands

FAQ

Q2: Getting 401 / 403 errors?

Q3: Connection failed?

Q4: `wire_api = "chat"` is no longer supported?

Q5: Tool calls or runs are failing?

Q6: Use environment variables instead of auth.json?

Q7: How do I switch models?

Q8: How do I check usage and billing?

Support and Help

Get Started with APIMart

Chat Applications

Development Tools

Application Platforms

Documentation Index

​Introduction

​Prerequisites

​Step 1: Install Codex CLI

​Verify the installation

​Step 2: Configure the APIMart API

​2.1 Locate the config directory

​2.2 Configure the API key

​2.3 Configure the model provider

​Step 3: Get Started

​Verify the configuration

​Interactive mode

​Approval modes

​Switch models

​Supported Models

​Common Commands

​FAQ

​Q1: A ChatGPT sign-in screen appears after launch?

​Q2: Getting 401 / 403 errors?

​Q3: Connection failed?

​Q4: wire_api = "chat" is no longer supported?

​Q5: Tool calls or runs are failing?

​Q6: Use environment variables instead of auth.json?

​Q7: How do I switch models?

​Q8: How do I check usage and billing?

​Support and Help

Get Started with APIMart

Introduction

Prerequisites

Step 1: Install Codex CLI

Verify the installation

Step 2: Configure the APIMart API

2.1 Locate the config directory

2.2 Configure the API key

2.3 Configure the model provider

Step 3: Get Started

Verify the configuration

Interactive mode

Approval modes

Switch models

Supported Models

Common Commands

FAQ

Q1: A ChatGPT sign-in screen appears after launch?

Q2: Getting 401 / 403 errors?

Q3: Connection failed?

Q4: `wire_api = "chat"` is no longer supported?

Q5: Tool calls or runs are failing?

Q6: Use environment variables instead of auth.json?

Q7: How do I switch models?

Q8: How do I check usage and billing?

Support and Help