Coding agent comparison
Frontier comparisonOpenAI Agents API vs OpenAI Codex: Complete Comparison
OpenAI Agents API is the public-beta API that exposes the Codex harness as a managed cloud runtime.
Featured · Updated today · Last verified: September 2026 · Score 96
Choose OpenAI Agents API when
App-owned durable agents that need OpenAI to run the Codex loop.
Choose OpenAI Codex when
Developers who want OpenAI's first-party coding agent in CLI, IDE, or ChatGPT.
Short verdict
Same vendor, different product. API harness vs coding app.
Key differences
Who starts the session and who provisions the environment.
Best for
Match the caller: your backend or a developer.
Reasoning fit
Pin the model ID in both. Do not mix product names in evals.
Coding workflow fit
Codex for diffs a human reviews. Agents API for work your app continues.
Multimodal fit
Neither is ChatGPT Images.
Enterprise fit
Agents API residency is US-only today. Confirm Codex workspace controls separately.
Who should not choose this?
- Do not pick Agents API expecting the Codex CLI UX.
- Do not pick Codex expecting a public session API.
- Do not invent a ZDR path for Agents API.
Cost considerations
Agents API has no extra harness fee. Sandbox containers and tools still bill.
Limitations
Verified September 13, 2026.
Final recommendation
If you are embedding an agent, start with Agents API. If you are writing code yourself, start with Codex.