AI SDK - Codex Harness

HarnessV1 adapter backed by @openai/codex-sdk, which drives the codex CLI. The adapter ships a bridge process that runs inside a sandbox and talks to the host over a WebSocket on a sandbox-proxied loopback port.

Setup

npm i @ai-sdk/harness-codex @ai-sdk/harness @ai-sdk/sandbox-vercel

The bridge installs @openai/codex-sdk (and the codex CLI it depends on) inside the sandbox the first time the session starts.

Usage

import { HarnessAgent } from '@ai-sdk/harness/agent';
import { createCodex } from '@ai-sdk/harness-codex';
import { createVercelSandbox } from '@ai-sdk/sandbox-vercel';
import { tool } from 'ai';
import { z } from 'zod/v4';

const agent = new HarnessAgent({
  harness: createCodex(),
  id: 'demo',
  sandbox: createVercelSandbox({
    runtime: 'node24',
    ports: [4000],
  }),
  tools: {
    deploy: tool({
      description: 'Deploy a service.',
      inputSchema: z.object({ env: z.enum(['staging', 'production']) }),
      execute: async ({ env }) => ({ url: `https://${env}.example.com` }),
    }),
  },
  harnessOptions: {
    codex: { reasoningEffort: 'high' },
  },
});

Codex does not auto-discover a skills directory the way the claude CLI does, so when you supply skills: [...] on the factory the adapter injects every skill inline into the user prompt on each turn. Use fewer, larger skills rather than many tiny ones.

const agent = new HarnessAgent({
  harness: createCodex({
    skills: [
      { name: 'haiku-mode', description: 'Answer in haikus.', content: '...' },
    ],
  }),
  sandbox: createVercelSandbox({
    runtime: 'node24',
    ports: [4000],
  }),
});

const session = await agent.createSession();

try {
  const result = await agent.generate({
    session,
    prompt: 'List the files in this workspace and describe their purpose.',
  });
  console.log(result.text);
} finally {
  await session.destroy();
}

The adapter requires a HarnessV1SandboxProvider whose handles expose at least one port — @ai-sdk/sandbox-vercel is the supported choice today. The agent calls provider.createSession() when a session starts. Use session.detach() to park the bridge and sandbox, session.stop() to save state and stop the sandbox, or session.destroy() to clean up without keeping resume state.