OpenAI puts the Codex harness on Agents API public beta

OpenAI put the Codex harness on a public API. On 10 September 2026, OpenAI Developers on X said the Agents API is in public beta for cloud agents that run on the same harness OpenAI uses for Codex.

From that post: "Go from idea to a working agent faster with the Agents API. Build and run cloud agents with the Codex harness, fully managed by OpenAI. We handle orchestration, long-running sessions, and context management. You focus on what makes your agent unique. Available in public beta."

The ship post and developer overview describe a session you create with a model, tools, and an environment. OpenAI runs the loop: model calls, tool use, compaction, recovery. You pick where code and files live. Sample calls in the post use `gpt-6-astra`, MCP servers, and `multi_agent` with concurrent subagents.

Environments split three ways in the post: OpenAI-hosted sandboxes, your own infrastructure, or first-class partners named there (Blaxel, Cloudflare, Daytona, DigitalOcean, E2B, Modal, Oracle, Runloop, Vercel). Docs say model use, built-in tools, and hosted sandboxes bill at ordinary API rates. OpenAI says there is no extra Agents API fee.

Harness features named in the launch: automatic context compaction across long sessions, tool search plus programmatic tool calling, MCP and custom functions, web search, and parallel subagents. The company points to the open-source Codex repo as the logic it now operates as a service.

Key facts

• Public beta on 10 September 2026 for all developers, per OpenAI; the company says it will iterate toward general availability.
• Alert: @OpenAIDevs on X. Body primary: Introducing the Agents API.
• Endpoint shape in docs: `client.beta.agents.sessions.create`.
• Customer quotes in the post (eval lift, 4x latency cut, 60% cost cut, 86% fewer failed responses) are OpenAI-selected. They are not independent measurements.
• Same calendar day, OpenAI also posted GPT-Live-1 in the API and ChatGPT for Financial Services. Those are separate surfaces.

How to read this. Public beta is the access state OpenAI named. Token, tool, and hosted-sandbox bills still apply under the pricing page OpenAI linked. Partner names are integrations listed in the post.

Frontier Flux is not affiliated with OpenAI. The X post is the alert. Claims about reliability, cost, and latency stay vendor-reported until independently measured.