Codex CLI is OpenAI's command-line AI coding tool. It runs in your terminal and operates directly on your codebase. Since OfoxAI is fully compatible with the OpenAI protocol, you can integrate seamlessly.

Does setting OPENAI_BASE_URL override the default OpenAI endpoint?

Yes. When you set the OPENAI_BASE_URL environment variable, Codex CLI sends all API requests to that URL instead of the default OpenAI endpoint. Your OPENAI_API_KEY should be the key from your custom provider.

Which Codex CLI model should I use for everyday coding?

Use openai/gpt-5.4-mini-codex for code generation tasks. Switch to openai/gpt-5.1-codex-max for complex refactoring that requires deeper context understanding.

Can I use Codex CLI alongside other AI coding tools?

Yes. Codex CLI works in the terminal while tools like Cursor and Cline work inside editors. If all tools point to the same API provider, they share one API key and one billing dashboard.

Mar 30, 2026

codex-cliai-codingapi-setupopenai

How to Configure Codex CLI with a Custom API Endpoint (2026 Guide)

TL;DR

Codex CLI is OpenAI’s command-line AI coding tool. It runs in your terminal, takes natural language instructions, and generates or modifies code directly in your project. Since OfoxAI is fully compatible with the OpenAI protocol, you can integrate seamlessly with just two environment variables. This guide covers installation, configuration with OfoxAI, model selection, and verification.

For the official integration reference, see the OfoxAI Codex integration docs.

What Is Codex CLI

Codex CLI is a command-line tool published by OpenAI for AI-assisted coding. Unlike IDE extensions, it has no graphical interface. You type a natural language instruction in your terminal, and it generates code, modifies files, or performs refactors.

Typical use cases:

Scaffolding: Generate project structures and configuration files from a description
Refactoring: Describe the change you want and Codex CLI edits your source files
Batch operations: Rename, reformat, or apply consistent changes across files
Code explanation: Point it at unfamiliar code and ask for a walkthrough

Why Use a Custom API Endpoint

Codex CLI connects to OpenAI’s API by default. Routing through a provider like OfoxAI offers practical advantages:

Unified billing. If you use multiple AI tools, adding Codex CLI to the same endpoint means one API key, one invoice, and one usage dashboard.

Model access. An aggregation platform may provide access in regions where direct OpenAI connectivity is unreliable.

Cost management. Consolidating tools under one provider simplifies cost tracking.

Installation

npm install -g @openai/codex

After installation, the codex command should be available in your terminal. If it is not found, verify that npm’s global bin directory is in your $PATH.

Configuration

Codex CLI uses the OpenAI protocol — just configure two environment variables.

Step 1: Edit Your Shell Configuration

Add these lines to ~/.zshrc (or ~/.bashrc on Linux):

export OPENAI_API_KEY=<your OFOXAI_API_KEY>
export OPENAI_BASE_URL=https://api.ofox.ai/v1

Key points:

OPENAI_API_KEY is the key from your OfoxAI dashboard, not an OpenAI key
OPENAI_BASE_URL must include the /v1 path
No spaces around the = sign

Step 2: Reload the Configuration

source ~/.zshrc

Or open a new terminal window.

Step 3: Verify

Run a simple test:

codex "Create a Hello World Python script"

If Codex CLI generates code without errors, the configuration is working.

Model Selection

You can specify the model using command-line arguments:

# Use Codex default model
codex --model openai/gpt-5.4-mini-codex "Refactor this function"

# Use Codex Max (complex tasks)
codex --model openai/gpt-5.1-codex-max "Fix this bug"

Recommended Models

Scenario	Model
Code generation	`openai/gpt-5.4-mini-codex`
Complex refactoring	`openai/gpt-5.1-codex-max`

For most day-to-day work, gpt-5.4-mini-codex is the practical choice — lower cost and faster responses. Reach for gpt-5.1-codex-max when you need the model to reason across multiple files or handle architectural decisions.

Practical Examples

Project scaffolding

codex "Create an Express.js project with TypeScript, ESLint, and a health check endpoint"

File conversion

codex --model openai/gpt-5.1-codex-max "Convert all JavaScript files in src/utils/ to TypeScript"

Test generation

codex "Write comprehensive Jest tests for src/services/auth.ts"

Troubleshooting

”Invalid API Key” error

Confirm that OPENAI_API_KEY in your shell profile is the key from your OfoxAI dashboard. Check for trailing spaces or line breaks in the copied value.

Connection timeout

Verify that OPENAI_BASE_URL is set to https://api.ofox.ai/v1. The protocol must be https and the path must include /v1.

Environment variables not loaded

Run echo $OPENAI_BASE_URL in your terminal. If the output is empty, run source ~/.zshrc again or open a new terminal.

Model not found

When using a custom provider, model IDs include a prefix. Use openai/gpt-5.4-mini-codex, not gpt-5.4-mini-codex.

A Note on Versioning

Codex CLI configuration options may change with version updates. See the Codex CLI official documentation for the latest information.

Summary

Configuring Codex CLI with a custom API endpoint takes two environment variables and under five minutes. Install the npm package, set OPENAI_API_KEY and OPENAI_BASE_URL in your shell profile, reload, and you are coding from the terminal with AI assistance.

For full integration documentation, see the OfoxAI Codex integration guide.