Run Your Agents on Codex
Agenta now ships three harnesses: Claude Code, Pi, and Codex. A harness is the program that drives the model, runs the tools it asks for, and manages context. You pick one per agent, and the rest of the agent does not move with it.
Picking Codex
Go to Sidebar > Agents > <agent name>, set Playground mode to Build, and open the Model & harness section at the top of the Configuration column. Click Detailed configuration, open the Harness section, and choose Codex. Then pick a model in the Model section below.
The models
| Model | Picker label | Context window |
|---|---|---|
| GPT-5.6 Sol | Sol (default) | 1,050,000 |
| GPT-5.6 Terra | Terra | 1,050,000 |
| GPT-5.6 Luna | Luna (cheapest) | 1,050,000 |
| GPT-5.5 | GPT-5.5 | 1,050,000 |
| GPT-5.2 | GPT-5.2 | 272,000 |
Sol is the strongest of the three 5.6 tiers, Luna is the fastest and cheapest, and Terra sits between them. The picker shows each model's price and its cost, intelligence, and speed ratings so you can compare before you switch.
Codex reaches OpenAI directly. Unlike Claude Code, it does not route through Bedrock, Vertex AI, or a custom gateway.
Tool approvals
Codex uses the same permission rules as your other agents. A tool set to allow runs, a tool set to deny is refused, and a tool set to ask stops the run and puts the question in front of you.
An ask parks the session warm. Answering resumes the session that was already running, keeping the original tool call, instead of paying for a cold start. Denying a tool ends the turn cleanly and reports the tool as denied rather than as an error.
This works on both the local sandbox and Daytona.
Tools, MCP, and attachments
Every tool you have configured on the agent works: Agenta's own tools, code tools, and connected integrations all reach Codex, with tracing and cost reporting attached as usual.
You can also point Codex at your own HTTP MCP servers, the same way you can with Claude Code. The MCP servers section appears in the agent configuration when you select Codex.
Codex reads image attachments natively. Paste or drag an image into the chat and the model sees it. Audio and document attachments are not supported on Codex today.
Paying for the model
Two options, the same two the other harnesses have:
- An API key. Add an OpenAI key to the agent and Agenta uses it for the run. This works on Agenta Cloud and on self-hosted deployments, on both sandbox types.
- Your ChatGPT subscription. When you self-host, an agent can authenticate from a ChatGPT/Codex login you already pay for, instead of metered API billing. This works on local runs only. A Daytona run cannot use a subscription, and the option is not available on Agenta Cloud.
Notes for self-hosters
If you run agents on Daytona, rebuild your sandbox snapshot before you use Codex there. Run the snapshot recipe with --force so agenta-agent-sandbox-v1 picks up the Codex build from this release. See Run agents in a cloud sandbox (Daytona).
To use a ChatGPT subscription, mount your ~/.codex login into the runner and set CODEX_HOME. See Use your own subscription.
Getting started
- Use your own subscription has the Codex login setup.
- Run agents in a cloud sandbox (Daytona) covers the snapshot rebuild.
- Permissions covers the approval rules Codex follows.