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Prerequisites

export OPENCOMPUTER_API_KEY=your-api-key
Grab your API key from app.opencomputer.dev.

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1. Create an agent (with your Anthropic key)

An agent is the reusable “what” — a name, a prompt, and a model. Sessions run the model on your Anthropic key, so pass it inline with key. It’s held in OpenComputer’s secret store (encrypted, write-only); the real key never enters the sandbox — it’s sealed, and a host proxy reveals it only on the outbound call to Anthropic, so it’s never exposed to the model or the agent’s code. 
curl https://api.opencomputer.dev/v3/agents \
  -H "Authorization: Bearer $OPENCOMPUTER_API_KEY" \
  -d '{ "name": "coder", "prompt": "You are a coding assistant.",
        "model": "anthropic/claude-opus-4-8", "key": "sk-ant-…" }'
# → { "id": "agt_…", "name": "coder", … }
Reusing one key across agents? Add it once via POST /credentials, set it as your default, and skip key here.

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2. Start a session

Start a session on the agent with a task. Add an optional webhook to receive every event from the start. 
curl https://api.opencomputer.dev/v3/sessions \
  -H "Authorization: Bearer $OPENCOMPUTER_API_KEY" \
  -d '{ "agent": "agt_…",
        "input": "Write a Python script that prints the first 20 primes, run it, and report the output.",
        "webhook": "https://your.app/oc-webhook" }'

{
  "session": { "id": "sess_abc", "status": "queued", "head": 1, "input_cursor": 0 },
  "client_token": "ct_…"     // session-scoped; safe to hand to a browser (read + steer)
}
Reuse the agent across as many sessions as you like. To bound a run, pass limits: { tokens?, turn_seconds?, turns? } on the agent or the session.

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3. Stream it live

Open an EventSource with the client_token from the create call. It rides the query string — browsers can’t set headers on EventSource, so the scoped client token goes in the URL (never your API key). level=user shows only what an end user should see (see levels). 
const es = new EventSource(
  `https://api.opencomputer.dev/v3/sessions/${id}/events?stream=sse&level=user&token=${clientToken}`
);
es.onmessage = (e) => render(JSON.parse(e.data)); // each event: { seq, actor, type, level, body, … }
Resume is automatic. Each event carries its seq as the SSE event id, so on a dropped connection EventSource reconnects and resends Last-Event-ID — you pick up exactly where you left off, no bookkeeping. (Pass after=<seq> on the URL to start from a specific point.)

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4. Steer it

Send a follow-up at any time. The session wakes and continues with its prior context. 
curl https://api.opencomputer.dev/v3/sessions/$ID/messages \
  -H "Authorization: Bearer $CLIENT_TOKEN" \
  -d '{ "text": "also check the CI config", "idempotency_key": "nudge-1" }'

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5. Manage destinations (optional)

You already passed a webhook at create. Add or manage more destinations later — each receives events from when it’s created (earlier events aren’t backfilled yet). 
curl https://api.opencomputer.dev/v3/sessions/$ID/destinations \
  -H "Authorization: Bearer $OPENCOMPUTER_API_KEY" \
  -d '{ "url": "https://your.app/oc-webhook", "secret": "whsec_…", "level": "user" }'
Deliveries are signed (Standard Webhooks) and retried; dedupe by webhook-id. See Webhooks to verify the signature and inspect deliveries.

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Next steps

Sessions

How a session works — lifecycle and events.

Webhooks

Deliver output reliably, and control deliveries.

Example apps

A repo of examples built on this API.