OpenAI Codex Guide: CLI, IDE Extension and Codex Cloud

Last checked: 2026-11-09 · Sources: Codex CLI docs↗, Codex pricing and limits↗, IDE extension↗, Codex Cloud↗, GitHub openai/codex↗

#Quick answer: what is Codex, how do I install it and what does it cost?

Codex is OpenAI's coding agent. It reads your repository, edits files, runs commands and hands you a diff to review. One account works in four places: the Codex CLI in your terminal, the IDE extension in VS Code-based editors, Codex Cloud inside ChatGPT, and the ChatGPT desktop app. The CLI is written in Rust and open source under Apache-2.0.

As of 2026-11-09:

• Install: npm install -g @openai/codex or brew install --cask codex; the current version is 0.167.0. There is also an official install script.
• Full CLI, IDE and cloud use starts with ChatGPT Plus: $20/month, with GPT-6.1 Sol and GPT-6 Luna.
• Free ($0) and Go ($8/month): GPT-6 Luna at standard speed in the desktop app only, subject to rollout.
• Pro: $100, $200 or $500 per month; OpenAI says Pro currently has no five-hour limit.
• Business: $20 per user per month billed annually (2+ users), $25 billed monthly; Enterprise and Edu by quote.
• API key: billed at API prices, for example gpt-6.1-sol at $2 input / $10 output per million tokens.

#Which ways can I use Codex?

codex cloud in the terminal lists cloud tasks, submits new ones and applies results to your local repo.

#How do I install the Codex CLI?

bashCopy
# macOS / Linux install script (run it again to update)
curl -fsSL https://chatgpt.com/codex/install.sh | sh

# npm
npm install -g @openai/codex

# Homebrew
brew install --cask codex

Windows PowerShell:

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

Run codex in a project folder. On first run choose Sign in with ChatGPT or another sign-in method such as an API key. Commit before and after each task so you can revert.

#How much can I use on Plus?

OpenAI gives these ranges of local messages per five hours for Plus and standard Business seats:

The ranges are wide because one message can read a few files or hundreds. Cloud tasks use more of the allowance than local messages, and weekly limits may also apply; OpenAI publishes no numbers for those. GPT-5.5 was retired from Codex with ChatGPT sign-in on 2026-10-14 (API-key sessions are not affected).

#How does AGENTS.md work?

AGENTS.md holds the project instructions Codex reads at the start of every run: build and test commands, conventions and no-go areas.

Lookup order from the official docs:

1. Global: ~/.codex/AGENTS.override.md, else ~/.codex/AGENTS.md (or the CODEX_HOME directory)
2. Project: from the project root (usually the Git root) down to your current directory; in each directory Codex checks AGENTS.override.md, then AGENTS.md, then names in project_doc_fallback_filenames, taking at most one file per directory
3. Files are joined root first, so files closer to your current directory win
4. The combined size stops at project_doc_max_bytes, 32 KiB by default

tomlCopy
# ~/.codex/config.toml
project_doc_fallback_filenames = ["TEAM_GUIDE.md", ".agents.md"]
project_doc_max_bytes = 65536

Check what loaded:

bashCopy
codex --ask-for-approval never "Summarize the current instructions."

#How do sandbox and approvals work?

• workspace-write has no network by default, so npm install fails until you enable network access in config.
• .git, .codex and .agents inside the workspace stay read-only.
• approval_policy = "untrusted" is no longer supported.
• Use /permissions to switch during a session and /model to change model and reasoning effort.

#Useful commands

Comment @codex review on a GitHub pull request to have Codex review it in the cloud.

#Codex vs Claude Code vs Cursor

Prices as of 2026-11-09; see Claude pricing↗ and Cursor pricing↗.

• You already pay for ChatGPT Plus: start with Codex. Cloud tasks and GitHub PR reviews are where it saves the most effort.
• Your team lives in the terminal: run the same real task in Codex and Claude Code before you decide.
• You prefer editing in an editor: Cursor feels smoother, and the Codex extension also installs in Cursor.

All three read AGENTS.md, so one file of team rules works everywhere.

#FAQ

Is this the 2021 Codex model? No. The 2021 Codex was a code-completion model and was retired long ago. Today's Codex is OpenAI's coding agent product running current GPT models.

Can company code go into Codex Cloud? Cloud tasks connect to GitHub and install dependencies in a cloud environment. For sensitive code, have an admin confirm the ChatGPT workspace data and network policies first, or stay with the local CLI and IDE extension.

Can a Free account use the Codex CLI? As of 2026-11-09 the pricing page lists GPT-6 Luna in the desktop app for Free and Go, subject to rollout. Full CLI, IDE and web use starts with Plus, or pay per token with an API key.