Vercel Sandbox vs Fly Machines Fly Machines are 28% cheaper per agent run

Which is better, Vercel Sandbox or Fly Machines?

It depends on whether you want a sandbox service or VMs you manage. For agents that mostly wait on a model, Runtime is a sandbox API whose pause and forks keep memory. The job below costs $0.64 there, against $1.53 on a Fly Machine and $2.12 on Vercel. Pick Vercel Sandbox if the app lives on Vercel, with up to 10,000 sandboxes running in parallel on Pro. Pick Fly Machines for general VMs of up to 128 GB, with volumes and Managed Postgres beside them.

At a glance

Both rivals are priced in Ashburn: Vercel's default iad1 region and Fly's iad.

Is a Fly Machine cheaper than Vercel Sandbox?

At this size, yes, for almost any job. A performance-2x Machine costs $0.0916704 an hour however busy it is. Vercel's memory alone, 4 GB at $0.0212 a GB-hour, is $0.0848 an hour. By the time a Vercel sandbox has paid for its memory, it has nearly paid for the whole Machine. Vercel costs more as soon as a one-minute run uses about 3 CPU-seconds. With both CPUs busy, it costs almost four times as much.

A Machine's performance vCPUs are whole cores kept for it. A shared-cpu-2x Machine with 4 GB costs about $0.59 for the same 1,000 runs. Its shared vCPUs are guaranteed 6.25% of a core each, with a small burst allowance, so a new one would not fit 20 CPU-seconds into the minute.

What the Machine does not give you is a sandbox API. You create and destroy Machines yourself through the Machines API. You also add a volume if files must outlive the Machine's temporary root disk. Runtime and Vercel create a sandbox in one call. Runtime's default CPU is shared and billed as measured. cpu: "reserved" keeps every vCPU for the sandbox, as a performance Machine does.

TypeScriptimport { Runtime } from "withruntime";const runtime = new Runtime();const box = await runtime.sandboxes.create({  vcpu: 2,  memoryMiB: 4096,  timeoutSeconds: 120,  onLeaseEnd: "stop", // gone when the job ends, like a destroyed Machine});try {  await box.files.write("/workspace/invoice.py", "print(sum([125, 250, 375]))\n");  console.log((await box.exec(["python3", "/workspace/invoice.py"], { check: true })).stdout);} finally {  await box.stop();}

Cost for the same job

The job behind the headline: 1,000 runs, 60 seconds each, 20 CPU-seconds of work, on 2 vCPU with 4 GiB (4 GB on Vercel), against a performance-2x Machine with 4 GB.

For a month of 100,000 runs, the totals are $212.44 on Vercel, $152.78 on Machines and $63.89 on Runtime. With both CPUs busy for the whole minute, it is $1.33 on Runtime, $5.68 on Vercel and $1.53 on Machines. The Machine is priced as destroyed at the end of each run. Plan fees, creation charges, storage, network and free allowances do not appear in the totals.

Which one to pick

• Vercel Sandbox, when the application already lives on Vercel and the sandboxes should share its account. Pro allows up to 10,000 running at the same time.
• Fly Machines, when you want general-purpose VMs and are happy to manage them, need sizes up to 128 GB, or want volumes and Managed Postgres next to them.
• Runtime, when you want a sandbox API rather than raw VMs. It is priced 58% under a Machine and 70% under Vercel, with pause and forks that carry memory and running processes.

Moving to Runtime

Vercel Sandbox code keeps its shape with a new import, and no longer needs a Vercel project or token:

TypeScriptimport { Sandbox } from "withruntime/vercel"; // was: from "@vercel/sandbox"

Pythonfrom withruntime.vercel import sandbox  # was: from vercel import sandbox

On Fly, the usual pattern is one Machine created per job through the Machines API. Swap each of those for a Runtime sandbox created for the job and stopped at the end, as the sample above does. Commands, files and teardown follow map the calls.

Credit you add within 30 days of signing up is matched, up to $1,000 in total. A coding agent can run the whole port from the single instruction in migration, on a branch and on the free usage. Detail: Runtime vs Vercel Sandbox, Runtime vs Fly.io.

Sources

Fly.io prices checked 25 October 2026.

Vercel Sandbox pricing rechecked 25 October 2026; the rest checked 25 October 2026.

• Vercel Sandbox pricing, Understanding Vercel Sandboxes
• Fly.io pricing, Machine CPU performance, Machine suspend and resume, Fly Volumes, Fly.io regions
• Runtime pricing

Facts on this page were checked on 26 October 2026.