Codex (OpenAI) — Definition
Codex is OpenAI's code-execution runtime — the engine that lets agents run code, handle multi-step execution, and interact with external systems inside Workspace Agents and related products.
Longer definition
Codex originated as OpenAI's code-generation model in 2021, later becoming the underlying runtime for advanced agent behaviors. In 2026, Codex powers the execution layer of Workspace Agents — the ability for an agent to run Python code in a sandbox, chain tool calls with code logic, and handle multi-step workflows. When OpenAI says a product is "Codex-powered," they mean it uses this runtime for execution, not just model inference.
In practice
For most users, Codex is invisible — it's the engine behind the agent, not something you interact with directly. It matters when you're trying to understand what your agent can actually execute (code in a sandbox, not arbitrary code on your systems) and why certain execution latencies exist.
Common mistakes
- Thinking Codex means the agent can run code on your servers — it runs in OpenAI's sandbox, not your infrastructure
- Confusing Codex-the-runtime (2026) with Codex-the-original-model (2021) — related but not the same
- Expecting Codex-powered agents to handle tasks requiring persistent external servers — sandbox execution is ephemeral
See also
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