AI SDK - Claude Code Harness

HarnessV1 adapter backed by @anthropic-ai/claude-agent-sdk, which drives the claude 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-claude-code @ai-sdk/harness @ai-sdk/sandbox-vercel

The bridge installs @anthropic-ai/claude-agent-sdk and @anthropic-ai/claude-code inside the sandbox the first time the session starts.

Usage

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

const agent = new HarnessAgent({
  harness: createClaudeCode({
    skills: [
      {
        name: 'careful-refactors',
        description: 'Make minimal diffs and keep tests green.',
        content: 'Prefer changes that touch the fewest files possible.',
      },
    ],
  }),
  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: {
    'claude-code': {
      thinking: { type: 'adaptive', display: 'summarized' },
    },
  },
});

const session = await agent.createSession();

try {
  const result = await agent.generate({
    session,
    prompt: 'Read README.md and summarise the goals.',
  });
  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.

Runtime configuration

Use env to add environment variables to the Claude Code process. Configured values override variables inherited from the sandbox bridge process.

const harness = createClaudeCode({
  env: {
    DEPLOYMENT_ENV: 'staging',
  },
});