Sandboxer vs Fly.io Machines

Fly Machines are VMs that boot from container images and are managed through a REST API or flyctl, billed per second while running. They are a general app and compute primitive, not an agent sandbox product. Pick Fly for deploying apps close to users in many regions; pick Sandboxer for a full-VM workspace with agents preinstalled.

Checked against Fly.io Machines' public docs on October 27, 2026. Sources are linked in the table and listed below.

At a glance

Sandboxer and Fly.io Machines compared
Capability	Sandboxer	Fly.io Machines
Isolation	microVM Cloud Hypervisor, its own kernel	VM (described as fast-launching VMs) Isolation technology is not named on the pages fetched.
Full Linux with root	Ubuntu 24.04, sudo, systemd	fly machine run --shell opens a root shell in an Ubuntu image.
Docker inside	Preinstalled	partial Machines boot from container images; running a Docker daemon inside is not documented on the pages fetched.
Nested virtualization (/dev/kvm)
Pause and resume with memory	Running processes come back	partial A suspend endpoint pauses a Machine and snapshots its state; resume is attempted but not guaranteed.
Fork a sandbox	Copy-on-write disk copy that boots fresh	partial fly machine clone copies a Machine as many times as you like, into chosen regions; carrying over memory state is not described.
HTTPS URL per port	Private with a token, or public
Longest session	No limit on paid plans Auto-stop is up to 30 days or off
Billing	Per second, flat rate per size Stopped sandboxes are free	per second while running Stopped Machines are billed only for their root filesystem at $0.15/GB/month; RAM beyond a CPU preset's included amount is $6/GB/month.
GPUs		The Machines API guest config has gpu_kind and gpus fields.
Self-host or open source
Regions	US East (Virginia) and EU Central (Finland)	choose a region per Machine Placement is best-effort and can fail if a region is out of capacity.

= not documented publicly.

Where Fly.io Machines is strong

Machines start in well under a second from stopped and are created from any container image.
Per-second billing, with stopped Machines costing only root filesystem storage.
Region choice per Machine, and GPU configuration through the Machines API.
Suspend/resume snapshots exist in the API.

Where Sandboxer differs

Fly Machines are built from container images; a Sandboxer sandbox is a complete Ubuntu 24.04 VM with its own kernel, systemd and Docker preinstalled.
Fly's suspend resume is described as not guaranteed; Sandboxer stop saves memory and disk and resume brings processes back.
Fly Machines have no coding agents preinstalled or prompt API; Sandboxer ships six agents and a streamed prompt API.
Fly offers many regions and GPUs; Sandboxer runs in us-east and eu-central and has no GPUs today.

Pick Fly.io Machines if

You deploy apps or services across many regions close to users.
You need GPU Machines or want to build on a low-level machines REST API.
You already run workloads on Fly and want per-second VM compute.

Pick Sandboxer if

You need a full Ubuntu 24.04 VM with root, systemd, Docker and nested KVM rather than a container or job runner.
You want stop to save memory and disk and resume to bring running processes back, with stopped sandboxes costing nothing.
You want coding agents (Claude Code, Codex, OpenCode and others) preinstalled and driven through a prompt API, with per-second billing.

Sources

Products change. If something here is out of date, email hello@sandboxer.com and we'll fix it. Fly.io Machines is a trademark of its owner. Sandboxer is an independent product and is not affiliated with Fly.io Machines.

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