Antigravity CLI is Google's terminal agent, started with agy. OpenAI Codex is OpenAI's coding agent, available as a command-line tool, an IDE extension and a cloud service. Both let you ask for changes in plain English.
The short version
| Antigravity CLI | OpenAI Codex | |
|---|---|---|
| Made by | OpenAI | |
| What it is | Terminal agent (also linked to Google's Antigravity desktop app and IDE) | CLI, IDE extension and cloud service |
| Open source | Not stated in Google's docs | Yes |
| Sign-in | Personal Google account, Google Cloud, or Gemini API key | ChatGPT account or API key |
| Free plan | Yes, an Individuals plan with basic weekly rate limits | Included with ChatGPT plans (a Free plan is listed for quick tasks, so check limits), or use API credits |
| MCP servers | Yes | Yes |
| Project instructions | AGENTS.md or GEMINI.md | AGENTS.md |
| Skills | Yes | Yes (SKILL.md) |
| Install | One-line installer for macOS, Linux and Windows | npm install -g @openai/codex, Homebrew or an install script |
Pricing changes. See Google's pricing page and OpenAI's Codex page for current details.
What they have in common
- Plain-English changes across files. Both are agents, not just autocomplete.
- MCP. Both can connect to MCP servers (a standard way to plug extra tools into an AI).
AGENTS.md. Both read it, so one instructions file can serve both tools.- Skills. Both support reusable skills.
Key differences
Cost to try. Google's pricing page lists a $0 Individuals plan for Antigravity, with basic weekly rate limits. Codex is included with ChatGPT plans, and OpenAI's page also shows a Free plan whose contents aren't clear, so check before relying on it. You can also use an OpenAI API key and pay API rates.
Where you can use it. Codex comes as a CLI, an IDE extension and a cloud service. Antigravity CLI is terminal-first. Google's docs describe separate IDE extensions and a desktop app for the wider Antigravity platform.
Open source. Codex is open source. Google's Antigravity CLI docs don't state a licence. If reading and forking the code matters to you, Codex has the clearer answer. Google's older Gemini CLI is Apache 2.0, see Gemini CLI vs OpenAI Codex.
Which AI is behind it. Antigravity CLI offers Gemini models, and Google's docs list some other models too. Codex uses OpenAI's models. We haven't compared how good each is, so try both on your own code.
Do they work together?
Yes. They're separate command-line tools, so you can install both and try the same task in each. Keep a git safety net first: see our git guide.
Who should pick what
- You already pay for ChatGPT: Codex fits naturally.
- You have a Google account and want a free start: Antigravity CLI.
- You want an IDE extension or cloud option from the same tool: Codex.
- You want one instructions file shared with other tools: either, since both read
AGENTS.md.
Our verdict
Pick the one that matches the account you already have. For other terminal-agent comparisons, see Antigravity CLI vs Claude Code and Claude Code vs OpenAI Codex. To get going with Google's tool, try our Antigravity CLI getting started guide.