Modal Sandboxes vs Vercel Sandbox
Answer in brief
Choose Modal Sandboxes for high-concurrency and GPU-backed sandboxes — RL rollouts, evals and coding agents at scale; choose Vercel Sandbox for teams on Vercel and agent builders who want microVM isolation, active-CPU billing and credential brokering. Modal Sandboxes uses gVisor or VM isolation; Vercel Sandbox uses Firecracker microVM isolation.
Modal Sandboxes vs Vercel Sandbox at a glance
| Attribute | Modal Sandboxes | Vercel Sandbox |
|---|---|---|
| What it is | Sandboxes on Modal’s serverless compute platform for running untrusted code at very high scale, with GPUs, snapshots and tunnels. | Firecracker microVM sandboxes on Vercel’s infrastructure, persistent by default and billed on active CPU, with fine-grained egress control. |
| Isolation | gVisor by default, or VMs with their own Linux kernel; GPU sandboxes use gVisor | Firecracker microVM with a dedicated kernel per sandbox |
| Open source | No (Client SDK Apache-2.0) | No (SDK and CLI Apache-2.0) |
| Self-host / BYOC | No / Not documented | No / No |
| SDKs | Python, JavaScript/TypeScript, Go | JavaScript/TypeScript, Python |
| Cold start (vendor claim) | Sub-second, including for large custom images (vendor claim) | “Start in milliseconds” (vendor claim, no figure); snapshot resume faster than fresh start |
| Max session | 5 minutes default, configurable up to 24 hours; snapshots carry state beyond that | 5 min default; up to 45 min per session on Hobby and 24 hours on Pro/Enterprise; persistent sandboxes can be resumed indefinitely |
| Persistence | Filesystem snapshots, directory snapshots, memory snapshots (alpha) and Modal Volumes | Persistent by default — filesystem auto-snapshotted on stop and restored on resume; manual snapshots; Drives (beta) and S3 mounts |
| GPU | Yes — Modal’s full GPU range (T4 to B300) at standard per-second rates, e.g. H100 $0.001097/s | Not documented |
| Networking | Outbound open by default; block all, CIDR allowlists or domain allowlists (beta), updatable at runtime; encrypted tunnels with public URLs and connect tokens | Firewall modes allow-all, deny-all or domain/CIDR rules, updatable at runtime; credential brokering injects headers so secrets never enter the sandbox; public URLs for up to 15 ports |
| Pricing | Per second at sandbox (non-preemptible) rates: $0.00003942 per physical core-second (1 core = 2 vCPU) + $0.00000667 per GiB-second; GPUs at standard rates. Team plan $250/month | Active CPU $0.128/hour (billed only while CPU is used) + provisioned memory $0.0212/GB-hour + $0.60 per million creations, plus storage and transfer (iad1 rates) |
| Compliance | SOC 2 on all plans; HIPAA on Enterprise | Runs on Vercel infrastructure with SOC 2 Type II (company-wide) |
| Best for | High-concurrency and GPU-backed sandboxes — RL rollouts, evals and coding agents at scale | Teams on Vercel and agent builders who want microVM isolation, active-CPU billing and credential brokering |
Verified November 8, 2026 from each provider’s documentation. Cold-start figures are vendor claims, not our measurements.
Which should you choose?
Choose Modal Sandboxes if…
- You need very high concurrency (RL, evals, batch agents)
- You need GPUs inside the sandbox
- You already use Modal for inference or training
- You want Go as well as Python and TypeScript SDKs
Choose Vercel Sandbox if…
- You deploy on Vercel or use the AI SDK
- You want secrets brokered outside the sandbox
- Your agents idle while waiting on models and you want active-CPU billing
- You want persistent-by-default microVMs
Both are worth piloting with your own image and region. See the full Modal Sandboxes profile and Vercel Sandbox profile, or the complete comparison.
Frequently asked questions
Is Modal Sandboxes or Vercel Sandbox better for AI agents?
Neither is better for every workload. Modal Sandboxes is best for high-concurrency and GPU-backed sandboxes — RL rollouts, evals and coding agents at scale. Vercel Sandbox is best for teams on Vercel and agent builders who want microVM isolation, active-CPU billing and credential brokering.
Which is open source, Modal Sandboxes or Vercel Sandbox?
Neither is open source.
How do Modal Sandboxes and Vercel Sandbox isolate code?
Modal Sandboxes: gVisor by default, or VMs with their own Linux kernel; GPU sandboxes use gVisor. Vercel Sandbox: Firecracker microVM with a dedicated kernel per sandbox.
Sources
Cite this page
Agent Sandboxes. (2026). Modal Sandboxes vs Vercel Sandbox. agentsandboxes.org. Last reviewed November 8, 2026. https://agentsandboxes.org/compare/modal-vs-vercel-sandbox/
Found an error or a missing sandbox? Submit a correction — every entry links to the sources it relies on.