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Use the Codex backend when you want Codex to run the turns for a room-connected process agent. MeshAgent owns the room-facing runtime: the agent participant, channels, deployment, routing, and stored thread history. Codex handles each turn behind that process agent. This is different from using MeshAgent with Codex CLI or Codex Desktop. If you want to run Codex normally and route model traffic through the MeshAgent LLM Proxy, use meshagent setup or meshagent launch codex; see Use Codex and Claude with MeshAgent. A Codex-backed process agent creates an agent participant in a room and sends that participant’s turns to Codex app-server.

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Run locally

Start a chat agent in the gettingstarted room:
Open the same room in MeshAgent Studio and chat with codex-agent. While the command is running, the agent is connected to the room. You can test it in Studio like any other process agent because the room, participant, and chat channel are still managed by MeshAgent. Stop the local process when you are done testing.

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Select the Codex backend

Use --backend codex for the default Codex-backed process agent. Use --model codex/gpt-5.5 when you need to pin a specific Codex model.
If you pass a normal model name such as --model gpt-5.5, the process agent uses the standard LLM backend. That path sends turns through MeshAgent’s LLM adapters. If you pass a Codex model path such as --model codex/gpt-5.5, the process agent uses the Codex backend. --model can be repeated when you want to choose the exact models the agent can switch between. --backend is broader: it makes a backend’s default model set available. --backend codex currently adds codex/gpt-5.5. --backend llm currently adds llm/openai/gpt-5.2 and llm/anthropic/claude-3-5-sonnet-latest. If you omit both --backend and --model, the process command defaults to --model gpt-5.5, which is a standard LLM-backed agent. You can also make both backends available from the same agent by passing both models:
This uses the default dataset-backed process-agent thread storage, so the room thread remains the durable history while the selected model can change. In chat, use /models to list available models, then use /model codex/gpt-5.5 to switch to Codex or /model gpt-5.5 to switch back to the standard LLM backend. Do not use --thread-storage codex for a mixed-backend agent; Codex thread storage only supports Codex backends.

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Deploy the agent

When the local version works, deploy the same agent so it stays available without your terminal open:
This creates or updates a room service for codex-agent.

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Pin a Codex model

Use this form when you need to choose an exact Codex model. Otherwise, prefer --backend codex so the process agent uses the default Codex model.

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How it works

The process agent still runs through MeshAgent, but turn execution moves to Codex:
  1. meshagent process joins the room as codex-agent.
  2. The chat channel turns room chat into process-agent turns.
  3. The process supervisor routes each turn to the selected backend.
  4. The Codex backend starts the local Codex app-server and sends the turn to it.
  5. Codex app-server runs the Codex thread with Codex’s native coding-agent runtime.
  6. MeshAgent records the thread history using the default dataset-backed process-agent storage.
Codex app-server is the local Codex runtime used by the Codex SDK. OpenAI describes it as a local app-server controlled over JSON-RPC. MeshAgent uses that runtime so the room participant can use Codex behavior while still using MeshAgent rooms, channels, deployment, and thread storage. See the OpenAI Codex SDK docs for the app-server client model. Use this instead of --model gpt-5.5 when you specifically want Codex’s coding-agent runtime behind the MeshAgent room participant. Use a normal model name when you need a standard LLM-backed process agent.

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Tool support

Codex-backed process agents use Codex app-server’s native runtime, not MeshAgent’s LLM tool pipeline. That means Codex app-server owns coding-agent behavior such as command execution, file changes, plans, sandboxing, approvals, and any MCP tools configured for Codex itself. MeshAgent receives those Codex events and records them in the process thread. MeshAgent also surfaces Codex diff updates as codex tool events in the turn stream so Studio can show code changes as part of the work. Use the standard LLM backend when the agent needs MeshAgent tool flags such as --require-toolkit, --tool-search, --web-search, --storage, --mcp, --shell, or --advanced-shell. Those flags add tools to LLM turns. Custom MeshAgent room toolkits are not exposed to Codex turns through --tool-search or --require-toolkit.

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