spark-vm vs E2B
E2B is the reference implementation of the task-scoped sandbox: Firecracker microVMs, SDK-first, templates-as-code — sold to developers who run agent code. spark-vm sells to the agent itself: a persistent computer that belongs to the agent, not a session it borrows. Different customer, different job — if your agent's work fits in a session, E2B is excellent at it.
| spark-vm | E2B | |
|---|---|---|
| What it is | A persistent computer for an agent: files, scheduled jobs, and a desktop that survive to tomorrow. | A task-scoped sandbox cloud for developers: Firecracker microVM per sandbox, SDK-first. |
| Persistence model | Always-on by design. State is the default, not a feature. | Sessions, capped. Hobby: 1-hour sessions; Pro: 24-hour sessions. State beyond that is an opt-in snapshot. |
| Scheduled work | Yes. Cron jobs live on the box and run whether or not a session is open. | No standing scheduler. Sandboxes are created per task; nothing runs between sessions. |
| Desktop | Yes. A real desktop the agent can drive. | No. Headless code execution. |
| Price shape | Self-host: free (MIT) + your hardware. Hosted: TBD, priced per box not per seat. | Hobby $0 + $100 one-time credit · Pro $150/mo + usage. Roughly $78/mo in usage to keep one continuous 2vCPU/512MB box alive. |
| Secrets handling | Credential proxy. The agent only ever sees hsurr: placeholders; real values swap on allowlisted hosts, every swap audited. |
Standard env-var secrets in the sandbox template. |
| Human approvals | Built in. Sensitive actions pause for a tap on your phone. | Yours to build. No per-action approval plane in the product. |
| Cold start | It's already running — there is no cold start. | Fast. Firecracker boots in the low hundreds of milliseconds. |
| Self-host option | Yes. MIT open source; runs on your Unraid/Proxmox/VPS today. | No. Hosted service only. |
When to pick E2B instead
Intellectual honesty first: E2B wins clearly when you're the developer buying compute for short-lived agent runs —
- Short tasksYour agent runs code, returns a result, and exits. Sessions up to 24h on Pro cover most of this.
- SDK-firstYou want to spin sandboxes from code with templates-as-code, at high concurrency.
- No opsYou don't want a machine to think about — not even someone else's managed one.
E2B raised a $21M Series A (Insight Partners, July 2025) to be the execution layer for agents. For that job, it's the incumbent for a reason.
When spark-vm is the better fit
When the customer is the agent, not the developer: Muse, Grok Bot, Dots, or whatever you're running. An agent that needs to keep things — files that accumulate over weeks, cron jobs that run overnight, a desktop it drives across sessions — and you want it powerful but never holding your raw secrets. That's the computer-shaped hole task sandboxes don't fill, because they were never built for the agent in the first place.