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OpenAI Codex — FAQs ​

General Questions about OpenAI Codex ​

What is OpenAI Codex and how can you use it?

OpenAI Codex is a descendant of GPT-3 trained specifically on large amounts of source code. It powers tools like GitHub Copilot and supports natural-language to code generation. You can use Codex through the OpenAI API, the ChatGPT interface (for coding tasks), and integrations like VS Code extensions.

Is OpenAI Codex free to use?

Codex itself is not free. You can try limited coding help in the free tier of ChatGPT, but full API usage requires a paid plan. GitHub Copilot, based on Codex, costs $10/month for individuals or $100/year.

What is the pricing of OpenAI Codex in 2025?

Codex access is bundled into the broader OpenAI API and ChatGPT plans:

  • ChatGPT Plus (GPT-4 access): $20/month
  • API access (gpt-4-turbo / gpt-4o): Pay-per-use, starting at $0.003 per 1K input tokens (for GPT-4o Mini)

Codex-style code generation is now part of GPT-4 models, especially GPT-4 Turbo and GPT-5 Codex variants.

How to access OpenAI Codex on GitHub?

You cannot download Codex itself on GitHub, but you can:

Where can I find OpenAI Codex discussions on Reddit?

Most Codex and Copilot discussions happen on:

  • r/OpenAI: General OpenAI topics
  • r/Copilot: Dedicated to GitHub Copilot
  • r/ChatGPT: Where developers often compare ChatGPT coding vs Codex

OpenAI Codex vs Claude Code: What's the difference?

  • OpenAI Codex: Built on GPT-3/4/5, specialized in code completion, integration with GitHub Copilot, broad API ecosystem.
  • Claude Code (Anthropic): Part of Claude models (Sonnet, Opus), designed for code reviews, safe execution, and reasoning across repositories.
  • Key difference: Codex is more integrated with GitHub and IDE tooling, while Claude Code emphasizes agentic reasoning, multi-step analysis, and safety.

Codex CLI Specific ​

What is Codex CLI?

Codex CLI is OpenAI's terminal-based coding agent that runs locally on your machine. It supports interactive sessions, non-interactive runs, approvals/sandboxing, MCP tool servers, and AGENTS.md project memory. (GitHub)

Getting started ​

How do I install Codex CLI?

  • npm: npm install -g @openai/codex
  • Homebrew (macOS): brew install codex
  • Release binaries: download from the latest GitHub release for macOS (x86_64/arm64) and Linux (x86_64/arm64). After extracting, rename the binary to codex. (GitHub)

How do I run it?

Open a terminal and run codex. The first run will guide you through sign-in or API-key setup. (GitHub)

Does it work with my ChatGPT plan?

Yes. Choose Sign in with ChatGPT and use your Plus/Pro/Team/Edu/Enterprise plan. API keys are also supported, but require extra setup/migration steps per the docs. (GitHub)

Where are the official docs?

The Codex CLI GitHub README links to Getting Started, CLI usage, Authentication, Configuration, Sandbox & approvals, MCP, and more. (GitHub)

Configuration & project memory ​

Where does Codex store its settings?

In ~/.codex/config.toml. The docs page "Configuration" lists supported options. (GitHub)

What is AGENTS.md? Is it like CLAUDE.md?

Yes—AGENTS.md is an open, simple format from OpenAI for guiding coding agents. Think of it as a predictable place in your repo for "how to work here" instructions (dev tips, test commands, PR rules). The spec and examples are public. Codex CLI recognizes this file for "memory with AGENTS.md." (GitHub)

Can I use external tools (web fetch, filesystem, etc.)?

Codex supports Model Context Protocol (MCP) servers. Enable them by adding an mcp_servers section to ~/.codex/config.toml. The CLI docs link to MCP setup/details. (GitHub)

Safety, sandbox & approvals ​

Will Codex modify files or run commands automatically?

Codex includes a sandbox & approvals flow. You can require approvals before edits/commands, and there's a documented safety model for controlling what Codex is allowed to do. See "Sandbox & approvals" in the CLI docs. (GitHub)

Can I run things in the cloud instead of locally?

OpenAI also offers Cloud Environments (separate from the local CLI) with ephemeral containers, persistent volumes, and an internet toggle for network access. This is part of "Codex Cloud," not the local CLI, but you can pair them. (OpenAI Developer)

Authentication ​

What auth methods are supported?

  • Sign in with ChatGPT (recommended for Plus/Pro/Team/Edu/Enterprise).
  • API key (requires additional setup; migration steps available).

The README's Authentication section covers both, including headless login notes. (GitHub)

Usage modes ​

Interactive vs non-interactive?

Besides the interactive TUI, Codex supports non-interactive/CI mode, running with a prompt as input, and verbose tracing. See the "Docs & FAQ" links in the README for examples. (GitHub)

Does Codex have "slash commands" like some other tools?

Codex CLI exposes documented flags/modes (e.g., non-interactive, tracing) rather than a slash-command system. Check CLI usage and Advanced sections for the exact switches. (GitHub)

Models & pricing ​

Which models does Codex use?

Codex routes to OpenAI platform models under your plan or API key. Model availability and pricing are defined by the OpenAI platform; see the official pricing page for current rates. (The CLI README defers to your plan/API configuration.) (OpenAI Platform)

Is there "zero data retention"?

OpenAI documents a Zero Data Retention (ZDR) option in the CLI docs. Check that page to understand scope and how to enable it. (GitHub)

Platform support ​

What OSes are supported?

Official release artifacts are provided for macOS (arm64/x86_64) and Linux (arm64/x86_64) via GitHub releases; Homebrew is supported on macOS. (Windows users commonly run Codex inside WSL or use Linux/macOS.) See the releases section in the README for the exact tarballs. (GitHub)

Troubleshooting ​

Login issues?

Use the Authentication docs (including "Login on a headless machine") and the issue linked from the README if sign-in fails. (GitHub)

Can I run Codex in CI?

Yes—there's a Non-interactive / CI mode guide in the docs. (GitHub)

Where do I turn on detailed logs?

See Tracing / verbose logging in the docs. (GitHub)

How Codex concepts map to the Claude-Code world ​

  • CLAUDE.md → AGENTS.md: Codex reads AGENTS.md as structured project guidance/memory. (GitHub)
  • MCP tools: Same underlying protocol. Configure MCP servers in ~/.codex/config.toml. (GitHub)
  • Plan/safety flows: Codex uses sandbox & approvals (a documented safety/permission model) rather than a specific "Plan Mode" toggle. (GitHub)
  • Cloud workspaces: Codex Cloud provides environments (containers, volumes, internet toggle). Use alongside CLI when you want managed infra. (OpenAI Developer)