Sandbox comparison · Reviewed July 2026
Fly Machines are fast-launching VMs controlled through a lower-level Machines API. Run Cloud wraps infrastructure in agent-oriented sandbox primitives while preserving a Fly-shaped migration path.
Fly.io Machines
Run Cloud
Detailed comparison
This comparison focuses on architecture and workflow rather than temporary prices or benchmark claims.
| Area | Fly.io Machines | Run Cloud |
|---|---|---|
| Runtime model | Fast-launching general-purpose VMs grouped into Fly Apps. | Firecracker microVMs packaged as managed agent sandboxes. |
| State | Stop, start, and suspend controls; suspend snapshots memory with best-effort resume. | Snapshot and copy-on-write fork semantics are designed for agent checkpoints and fan-out. |
| API level | Low-level Machines resource, configuration, leases, metadata, and networking. | Higher-level exec, files, previews, lifecycle, and compatibility APIs. |
| Operations | You compose apps, machines, volumes, routing, and sandbox policy. | Run Cloud manages the sandbox control plane and adjacent mobile runtime. |
| Migration path | Existing code imports Machines from @flydotio/machines. | Switch to @run-cloud/sdk/compat/fly and validate Fly-specific networking and volume behavior. |
Provider details were reviewed against the Fly Machines API documentation. Product capabilities change; validate requirements against current vendor documentation.
Choose Fly.io Machines
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Compatibility layer
Keep the provider-shaped entry point while you validate lifecycle, network, image, and storage behavior against your application.
import { Machines } from "@flydotio/machines";import { Machines } from "@run-cloud/sdk/compat/fly";FAQ
Fly Machines are general-purpose fast-launching VMs. Teams can build a sandbox platform on top, while Run Cloud provides agent-oriented sandbox lifecycle, file, command, preview, and state primitives directly.
No. The compatibility layer targets the Machines-shaped integration path, not every Fly App, volume, routing, lease, or private-networking feature.
Use Fly Machines when you want low-level regional VM control and are comfortable building the sandbox orchestration and policy layer yourself.
Use Run Cloud when you want a managed agent runtime, explicit snapshot and fork workflows, or a direct connection to iOS simulator and Xcode infrastructure.
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Bring one sandbox workflow, keep the familiar API shape, and measure the behavior that matters to your agents.
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