Some work needs a real machine
Most agent work is a model call and a tool call — neither needs a kernel. Some genuinely does: writing files, running a build, cloning a repo. That needs a real filesystem and process tree, not just an isolate. The question is how small a share of the fleet ever needs one, and how fast it can be given back.
Isolation and idle cost pull against each other
A container sleeps on a timer, not a condition — it only notices nothing has happened for a while, so every burst of work leaves a tail you pay for. Stronger isolation means a longer tail, and economics closer to a machine rented by the hour. It is the part of a serverless design that behaves least like one, and we would rather say so than have it found later.
You pay for an isolate, not a machine.
On isolated-vm we sustain 2,000 concurrent agents under an 8-second heartbeat at a p99 execution latency of 37.5 ms, across 16 pods on a single AWS m7i.8xlarge, at about 1.2 MB per agent. The runtimes below reserve 128–512 MB per sandbox as their own documented minimum.
| System | Isolation | Cold start | Resume | Fork | RAM / agent | Idle agent |
|---|---|---|---|---|---|---|
| Naïve | V8 isolateno VM | 2.79msisolated-vm | ~1mswarm resume | 1.55mscopy-on-write | 1.2MBisolated-vm | KBs of statestorage only |
| E2B | FirecrackermicroVM | <200ms | ~1sfrom pause | — | 512MBminimum | Paused VMper GiB |
| Modal | ContainergVisor | ~1s | ~1smem snapshot | — | 128MBminimum | Reserved |
| Morph | microVM | — | <250ms | <250ms | — | Reserved VM |
| Cloudflare | Container | 1–3s | — | — | 256MBminimum | Memory reserved |
Naïve: measured on the isolated-vm backend, AWS m7i.8xlarge, 2026-07-22 · the worker_threads fallback v1 ships is roughly 15x slower on create and 15–17x heavier per agent · at 4,000 agents p99 rises to 73.8 ms, over our 50 ms SLO · Others: published figures · July 2026
- Coming soonSandboxes Without Machines: A V8-Isolate Runtime for Massive Fleets of Resident Agents
- Status
- Research
- Focus
- Cost per box-second
- Surface
- Early / evolving
- Papers
- Sandboxes Without Machines (preprint)