01 / behavior
Agent
The model, system prompt, tools, MCP servers, and skills that define how Codex behaves.
Managed runtime for Codex
Run Codex like an autonomous engineer.
Codex Managed Agents gives you the harness, secure tool execution, and cloud runtime for long-running agent work. Instead of building your own loop, sandbox, and orchestration stack, you get a managed environment where Codex can read files, run commands, browse the web, and execute code efficiently.
Secure command, file, and web execution
Built-in prompt caching and compaction
Persistent sessions with server-side event history
Runtime topology
Four primitives, one managed control plane.
Model + tools
Agent
Define Codex behavior once.
Container template
Environment
Bring packages, files, and access rules.
Execution runtime
Session
Combine the agent and environment for a live task.
App I/O
Events
Send instructions in and stream tool/status updates out.
Core concepts
Everything in the platform maps to four runtime objects.
Agent, Environment, Session, and Events form the vocabulary of the system. The homepage keeps them visible because they are the shortest path to understanding how the product fits together.
02 / runtime
Environment
A configured container template with pre-installed packages, mounted files, and network rules.
03 / execution
Session
A running agent instance inside an environment, working on a concrete task and producing outputs.
04 / control plane
Events
Messages flowing between your application and the agent, including user turns, tool results, and status updates.
How it works
Start from a definition, then let sessions do the work.
The workflow is intentionally small: define Codex behavior, choose the runtime, launch a session, and keep steering it through events while the infrastructure stays managed.
01
Create an agent
Define the model, prompt, tools, MCP servers, and skills once, then reuse the agent by ID.
02
Create an environment
Provision a cloud container template with the packages, files, and access controls your workload needs.
03
Start a session
Launch an execution that binds the chosen agent and environment for a specific task.
04
Send events and stream responses
Push user input as events while Codex autonomously calls tools and streams back updates over SSE.
05
Steer or interrupt
Guide the session mid-run, interrupt it, or redirect it without rebuilding the whole runtime loop.
When to use it
Best suited for agent workloads that need durable infrastructure.
Codex Managed Agents is not just a UI wrapper around a model. It is a runtime layer for workloads that need time, tools, isolation, and a memory of what already happened.
Long-running execution
Handle workloads that span minutes or hours and require multiple coordinated tool calls.
Cloud infrastructure
Run inside managed containers with pre-installed packages, mounted files, and explicit network access.
Minimal infrastructure
Skip building your own agent loop, sandbox, and tool orchestration layer from scratch.
Stateful sessions
Keep a persistent file system and conversation history across multi-turn tasks and retries.
Ready to ship
Build the agent once. Launch sessions whenever the task shows up.
Start with the Quickstart to create your first managed session, then move into the API Reference when you are ready to wire it into your own application.