Running Codex for your users on a server? Vercel's new durable-harness can resume a crashed Codex turn, but Codex support is still experimental

#What changed

On October 20, Vercel released durable-harness, a package for running coding-agent harnesses (Pi, OpenCode, Codex, Claude Code, eve, fx) on Vercel so a session survives crashes, function timeouts, and redeploys. For Codex, every session gets its own Vercel Sandbox that runs codex app-server. Your Vercel Function only drives it: it sends messages, reads the stream, routes model calls through AI Gateway, and writes a durable log that mirrors Codex's rollout file. If a turn crashes, another function picks it up from the log, and if the Sandbox is gone, a new one is rebuilt with the same files.

#Who is affected

Teams building a product or internal tool that runs Codex on a server, for example long background jobs or a chat UI that hands work to Codex. If you only use Codex locally through a ChatGPT plan, nothing changes for you.

#What to do now

• Start from Vercel's Codex guide and import the adapter from durable-harness/codex.
• To change direction mid-task, send a message with kind steer instead of cancelling; Codex picks it up at its next model request.
• If the client stream drops, reconnect with the session ID and the last event cursor instead of resending the prompt. The turn keeps running on the server.
• Make your own tools safe to run twice. After a crash, Codex is told an interrupted call is safe to repeat, so it may run it again.
• Budget for AI Gateway model calls and Sandbox time, since that is where Codex's usage goes in this setup.

#What is not confirmed

Vercel marks Codex support as experimental and runs it only in a Sandbox, because Codex is a single-user CLI that keeps its state on disk and runs commands on its machine. Vercel has not said when it will leave experimental, and OpenAI has not commented on it. We checked Vercel's docs but have not run it ourselves.

Sources: Vercel's launch post on X (https://x.com/vercel/status/2112653833382027729) and Vercel's docs (https://vercel.com/docs/agent-harnesses/codex, https://vercel.com/docs/agent-harnesses).