OpenAI Launches Agents API Beta, Opening Up the Codex Harness

On September 10, OpenAI launched the Agents API public beta, opening the harness that powers Codex to all developers: a single API call specifying task, model, tools and compute environment creates an agent running in OpenAI's cloud with fully managed orchestration, long-running sessions and context management. Alongside it, OpenAI shipped an official hosted sandbox and pre-built integrations with sandbox providers, so developers no longer need to build their own agent infrastructure.

Confirmed

• The Agents API is in public beta, built on the Codex harness, with OpenAI-managed orchestration, long-running sessions and context management (m1/m2/m4)
• Per OpenAI, the agent loop runs on OpenAI infrastructure coordinating model calls, tool use and context; developers control capability boundaries and choose where code execution and file handling happen (m5)
• It reuses the sandbox and infrastructure behind Codex and ChatGPT Enterprise (m20)
• The official video demoed an agent investigating production incidents: connecting tools via MCP, following a runbook, and producing an evidence-backed report (m1); a companion Box demo showed multi-agent collaboration (m7)
• Sandbox options: bring your own or use a provider, with CPU/GPU/memory sizing, fully managed or in-VPC deployment, and file/secret storage choices; first-class integrations include nine vendors such as Blaxel, Cloudflare, Modal and Vercel (m6); Blaxel announced itself as an official self-hosted sandbox partner (m16)
• OpenAI also launched its own hosted sandbox where agents can run code, process files and produce artifacts; developers just supply files, install packages, and add skills and plugins (m9/m10)
• Daytona published a guide for running Agents API sessions on Daytona sandboxes with outbound-only registration and zero inbound ports (m14)
• Official documentation covers session management including creating/resuming sessions (m19); developer chefbrent shared hands-on use of the session management API (m18)
• The E2B team demoed an agent workbench built on the API (m4)
• Cloudflare shipped an official integration: engineer Jilles demoed running Codex in Cloudflare Containers with security isolation and D1, deploying a logged agent in about 4 minutes (m17/m20)
• Kevin Whinnery argues the API joins Claude Managed Agents as a new integration point where frontier labs programmatically expose their first-party agent harnesses (m8)

Why it matters

• @shaunralston argues the hard part of agent development was never the model but making AI work for hours—calling tools, remembering what was done, recovering from errors, and not drowning in logs; the Agents API builds that skeleton (m19)
• Developers are freed from building and operating their own harness and infrastructure, focusing on task definition and tool integration
• The open sandbox ecosystem (BYO or one of nine providers) runs in parallel with OpenAI's own hosted sandbox, accommodating different needs for isolation, cost and deployment flexibility

2026-09-11 ~ 2026-09-12 · 21 related posts

• [source] OpenAI launches Agents API public beta: fully managed cloud agents with Codex harness — OpenAIDevs · 2026-09-11
• OpenAI details Agents API: hosted agent loop, developer-controlled code execution — OpenAIDevs · 2026-09-11
• [source] OpenAI Agents API supports BYO sandboxes with Cloudflare, Modal, E2B, Vercel and more — OpenAIDevs · 2026-09-11
• [source] OpenAI adds hosted sandboxes: agents can run code, work with files, produce artifacts — OpenAIDevs · 2026-09-11
• OpenAI Launches Agents API: Hosted Codex Harness for Building Agents — OpenAI · 2026-09-11
• OpenAI Agents API Meets Cloudflare: Deploy a Logged Agent in 4 Minutes — craigsdennis · 2026-09-11
• OpenAI launches Agents API: sessions, orchestration and evals for hour-long agents — shaunralston · 2026-09-11
• OpenAI Agents API hits public beta; Cloudflare ships sandbox integration for cloud Codex agents — ritakozlov · 2026-09-11
• Run OpenAI Agents API sessions in Daytona sandboxes with zero inbound ports — mattturck · 2026-09-11
• OpenAI Agents API Enters Public Beta as E2B Ships Hosted Sandbox Workbench Demo — OpenAIDevs · 2026-09-12
• OpenAI launches Agents API public beta with managed Codex harness; Box demos multi-agent deal-room workflow — OpenAIDevs · 2026-09-12
• The dumb token pipe is over: OpenAI's Agents API beta makes agent harness APIs the new integration point — jxnlco · 2026-09-12
• OpenAI Agents API enters public beta; Blaxel named official self-hosted sandbox partner — Scobleizer · 2026-09-12

8 near-duplicate retellings: OpenAIDevs · nikunjhanda · Codeblix_Ltd · varunshenoy_ · irvinebroque · dkundel · AI寒武纪 · minchoi