Make Codex and Claude talk in Reason, step by step
Open Reason on the web or in the Mac app
Sign in at reasonmachines.com, or download the Reason app for macOS from reasonmachines.com/download. Both open the same Sessions. Sending work in Reason needs the 3-day trial, a paid plan or credits, also when it runs on your own subscriptions.
Connect your ChatGPT and Claude plans
Open Settings › Models. Connect a ChatGPT Plus, Pro or Business plan with Sign in with ChatGPT (or Codex sign-in), and a Claude Pro or Max plan with Connect Claude; OpenAI or Anthropic API keys work too. Connected accounts are listed by provider, as below.
Connect GitHub and start a Session
In Customize › GitHub, connect the repositories Reason may work in. Then start a new Session, name the repository and describe the task. Reason works on its own cloud computer, or on your Mac through the Mac app.
Pick the first model in the message box
The model picker in the message box lists each connected account's models, grouped by provider. Pick a Claude model to have Claude write the change, or an OpenAI model to start with Codex's models.
Ask the other model to review or answer
Say it in plain words and name the model, for example "have a helper on GPT-6 Luna from my ChatGPT account review this diff and tell me what it would change". Reason starts a helper on that model in the same checkout and branch, and its reply comes back into your Session, where Claude can answer it or apply the fixes; the helper's row shows which model and account it ran on. Started on an OpenAI model? Ask for a Claude helper the same way.
Keep going when a plan runs out
Each model runs on the account you picked and keeps that provider's limits. Hit your limit? Reason keeps going on your other connected accounts or Reason credits, and says so in the conversation.
What people tried to make Codex and Claude talk
| Copy-paste relay | Codex plugin for Claude Code | MCP bridges | Reason | |
|---|---|---|---|---|
| How it works | You paste one agent's plan or diff into the other and carry the answer back | OpenAI's Claude Code plugin adds slash commands that run Codex reviews and hand tasks to Codex from inside Claude Code | An MCP server (for example agent-link-mcp) lets one agent start another agent's command line as a collaborator | One Session on one model starts a helper on the other model; the reply comes back into the Session |
| Direction | Whichever way you carry it | Claude Code asks Codex | The host agent asks the ones it starts | Both ways: Claude can ask an OpenAI model, and the other way round |
| Setup | None | Install the plugin in Claude Code; needs a ChatGPT subscription (Free included) or an OpenAI API key, and Node.js | Install and configure an MCP server on your computer | Connect both plans in Settings › Models, in the web or Mac app |
| Where it runs | Wherever each agent runs | Your computer | Your computer | Reason's cloud computer, or your Mac |
| Costs | Each agent's own plan | Counts toward your Codex usage limits | Each agent's own plan | Each model on the plan you connect; Reason needs the trial, a plan or credits |
| Good for | A quick one-off second opinion | Codex reviews without leaving Claude Code | Agents consulting each other on one machine | Both models working the same repository and branch, with no terminal |
There's no built-in link between OpenAI's Codex and Anthropic's Claude Code: they are separate agents with separate context. These are the ways people connect them today, each fair for a different job.
How Reason differs
Copy-paste makes you the messenger, and the plugin and MCP bridges run on your computer and start from one agent. In Reason, both models work in the same checkout and branch, the reply lands in the conversation you're already in, and the work keeps running on Reason's cloud computer when your laptop is closed.
Already run Claude Code and Codex on your own computer and want those live sessions to message each other? Reason Network connects them, both ways and across computers, and it's free.
Connect other agents
Questions
Can Codex and Claude Code work on the same repo?
Yes. In Reason, the helper on the other model works in the same checkout and branch as your Session, so Claude and an OpenAI model review and edit the same code. Running both command-line agents yourself on one repository also works; give each its own branch or worktree so their edits don't collide.
Do Codex and Claude share context?
Not automatically: each model has its own context, and neither reads the other's conversation. In Reason, the Session hands the helper the task and what it needs to know, the helper reads the same files, and its reply comes back into the Session. Repository instructions help both: Codex reads AGENTS.md, Claude Code reads CLAUDE.md, and Reason reads both.
Is it free?
Partly. Connecting your ChatGPT and Claude plans adds no Reason fee for those models, which keep their own plans and limits, but sending work in Reason needs the 3-day trial, a paid plan (Pro is $50 a month) or credits. Reason Network, for live Claude Code and Codex sessions on your own computer, is free.
How is this different from the Codex plugin for Claude Code?
The plugin runs Codex from inside Claude Code on your computer, one way. Reason runs both models in one Session on your connected plans, in both directions, in the web or Mac app, on its own cloud computer. You can use both.
Do I need an API key?
No. Connect your ChatGPT plan with Sign in with ChatGPT and your Claude plan with Connect Claude in Settings › Models. API keys work too if you'd rather pay per use.
Is Reason made by OpenAI or Anthropic?
No. Codex is a product of OpenAI and Claude Code a product of Anthropic. Reason is built by Reason Machines and is not affiliated with or endorsed by either.