Cloudflare Sandbox vs smol machines

Both run each sandbox in its own microVM with its own kernel. Cloudflare Sandbox is a container inside the Workers platform that sleeps when idle and starts from a fresh disk, while smol machines is an open-source VM engine whose machines keep their files and can branch while running.

The companies and products

Cloudflare Sandbox

Cloudflare Sandbox SDK runs untrusted or AI-generated code in Linux containers on Cloudflare's network, driven from a Cloudflare Worker.

Each sandbox is a Cloudflare Container backed by a Durable Object, and each container runs in its own Firecracker microVM with its own kernel and network. You build a linux/amd64 image, pick an instance type of up to 4 vCPU and 12 GiB, and reach the sandbox through your own Worker. It suits teams already on Workers who want short-lived sandboxes that sleep when idle; for code that only calls known methods, Cloudflare also offers Dynamic Workers, which run JavaScript in V8 isolates.

Isolation: Firecracker microVM per container, own kernel and network
Largest instance: 4 vCPU, 12 GiB memory, 20 GB disk (defaults, can be raised)
Disk: Ephemeral by default: a container that sleeps starts again from a fresh disk
Plan needed: Workers Paid, $5 a month account minimum; not on the Free plan
Account limits: 1,500 vCPU, 6 TiB memory and 30 TB disk running at once
Placement: Instances spread across several regions of Cloudflare's network, nearest free one picked
Compliance: Cloudflare holds a SOC 2 Type II report

smol machines

smol machines makes fast, isolated Linux microVMs that run the same way on your laptop, in their hosted cloud, or on your own servers.

The core is smolvm, an open-source microVM engine built on libkrun, where each machine has its own guest kernel. smol cloud is the paid hosted service that runs fleets of those machines behind a REST API and Node, Python and Rust SDKs. It is built for developers who want one VM model from local development to production, with live branching of running machines.

Isolation: Hardware-isolated microVM with its own guest kernel (libkrun)
Company: Founded 2026, Y Combinator Spring 2026, San Francisco, team of one listed
Open source: smolvm engine and smol SDK are open source and run on macOS, Linux and Windows hosts
Guests: Linux only; no Windows or macOS guests
Regions: No region field in the cloud create API
Uptime SLA: 99.95% on Pro, Startup and Enterprise

Which use cases each one fits

For each use case, Battleships prices every sandbox provider on the same workload and sorts them from the cheapest monthly bill up. “13th cheapest of 345” means 12 of the other 344 providers run that workload, with every feature it needs, for less. “With limits” means the provider runs it but misses something, so it is listed after every full match. Open a use case for its whole ranking and what each provider misses.

Use case and its workload	Cloudflare Sandbox: price rank	smol machines: price rank	boat: price rank
Software factory 100 at once · 4 vCPU / 8 GB · 2,200 sessions of 8 h a month smol machines keeps the disk across stops and fits a long build session better than Cloudflare, whose disk resets on sleep; boat adds /dev/kvm, SSH and coding agents you drive from outside.	162nd of 367, with limits $1,543 a month	73rd of 367, with limits $604 a month	3rd cheapest of 367 $634 a month
Always-on AI employees 50 machines 24/7 · 2 vCPU / 4 GB	207th of 366, with limits $2,188 a month	148th of 366, with limits $1,038 a month	5th cheapest of 366 $657 a month
Code interpreter bursts 100 at once · 1 vCPU / 2 GB · 200,000 sessions of 1 min a month Both fit short code runs well: Cloudflare bills CPU only while busy and wakes on the next request, and smol machines has a one-minute minimum and a /code endpoint.	13th cheapest of 345 $144 a month	12th cheapest of 345 $140 a month	186th of 345, with limits $2,000 a month
Sandboxes for your users 300 at once · 2 vCPU / 4 GB · 30,000 sessions of 23 min a month Both fit sandboxes for your users, at $731 a month on Cloudflare and $531 a month on smol machines; boat fits too at $209 a month and adds a desktop per user.	9th cheapest of 361 $731 a month	7th cheapest of 361 $531 a month	Cheapest of 361 $209 a month
RL rollouts 1,000 at once · 2 vCPU / 4 GB · 1,000,000 sessions of 3 min a month smol machines can branch a running machine with its memory and processes, so many rollouts start from one prepared state; Cloudflare has no fork.	144th of 360, with limits $9,428 a month	111th of 360, with limits $6,978 a month	34th of 360, with limits $2,000 a month
Agent evals 250 at once · 4 vCPU / 8 GB · 15,000 sessions of 20 min a month	45th cheapest of 364 $818 a month	36th cheapest of 364 $670 a month	10th cheapest of 364 $200 a month
CI runners 40 at once · 8 vCPU / 16 GB · 6,000 sessions of 12 min a month CI that builds Docker images fits smol machines better, since Cloudflare caps disk at 20 GB by default and turns off iptables for Docker; boat adds /dev/kvm for Android builds.	301st of 377, with limits $704 a month	66th cheapest of 377 $514 a month	4th cheapest of 377 $86 a month
24/7 dev boxes 1 machine 24/7 · 4 vCPU / 8 GB Cloudflare starts from a fresh disk after sleep, smol machines keeps files but bills the disk while stopped, and boat stops at no cost with its disk kept.	70th cheapest of 368 $93 a month	216th of 368, with limits $29 a month	18th cheapest of 368 $26 a month
Computer-use agents 50 at once · 4 vCPU / 8 GB · 20,000 sessions of 15 min a month Neither ships a desktop: Cloudflare removed its built-in one and smol machines only has a guide for your own Chromium; boat streams a 60fps desktop with computer use.	166th of 369, with limits $460 a month	90th of 369, with limits $156 a month	6th cheapest of 369 $200 a month
Browser-use agents 50 at once · 2 vCPU / 4 GB · 30,000 sessions of 10 min a month	210th of 367, with limits $233 a month	176th of 367, with limits $136 a month	7th cheapest of 367 $200 a month
Scraping & bots (startup scale) 50 at once · 1 vCPU / 2 GB · 100,000 sessions of 3 min a month	250th of 346, with limits $286 a month	241st of 346, with limits $242 a month	6th cheapest of 346 $90 a month
Mass scraping & bots (undetectable) 1,000 at once · 1 vCPU / 2 GB · 3,000,000 sessions of 2 min a month	169th of 338, with limits $5,741 a month	148th of 338, with limits $4,344 a month	71st of 338, with limits $1,800 a month
Parallel red teaming 200 at once · 2 vCPU / 4 GB · 5,000 sessions of 30 min a month Red-team runs often need nested VMs and raw networking; Cloudflare cannot change iptables or take raw TCP, smol cloud has no nested virtualization, and boat has both.	239th of 360, with limits $325 a month	252nd of 360, with limits $377 a month	2nd cheapest of 360 $200 a month
GPU eval jobs 10 at once · 8 vCPU / 32 GB · 500 sessions of 30 min a month	Can't run it	Can't run it	Can't run it
macOS agents 5 at once · 4 vCPU / 8 GB · 1,000 sessions of 20 min a month	Can't run it	Can't run it	Can't run it

Key features

Feature	Cloudflare Sandbox	smol machines	boat
Isolation	Firecracker microVM per container, own kernel and network	libkrun microVM with its own guest kernel	Full VM with its own kernel on dedicated AMD Ryzen 9 9950X hosts
Biggest machine	4 vCPU / 12 GiB / 20 GB disk by default (can be raised)	Up to 32 vCPU / 32 GB on Startup, 16 vCPU / 24 GB on Pro	Up to 16 vCPU / 32 GB on the $100 plan and above
Files after a stop	Fresh disk after sleep; snapshots (public beta, 30 days) or R2 backups if your code saves them	Filesystem survives a stop, /tmp is emptied; stopped disk keeps billing	Disk saved every minute and on stop; a stopped sandbox costs nothing
Fork	No fork; restore a saved snapshot or backup into a new sandbox	Branch a running machine with its memory and processes	Fork a running sandbox with its disk, without stopping it
Wake on request	Sleeps after inactivity and wakes on the next request	A command or terminal starts a stopped machine; idle apps wake on the next request	No; a stopped sandbox is started by API
Docker inside	docker:dind with iptables and IP forwarding turned off	Docker inside the VM, with its data on the machine's ext4 disk	Full Docker, root and systemd
Nested virtualization	Not documented	Not exposed in the cloud API; a local smolvm flag only	Yes, /dev/kvm for Android emulators and VMs
Inbound traffic	HTTP and WebSocket previews through your Worker; no raw TCP or public IP	Up to 16 published ports through a returned URL; no dedicated IP	HTTPS URLs for up to 50 ports, token-protected; raw TCP; dedicated IPv4 or IPv6
Outbound rules	allowedHosts deny-by-default list plus outbound handlers you write in Worker code	Blocked, open, or an allowlist of hosts and CIDR ranges	Open internet, no provider-side allowlist
Keeping API keys out of the sandbox	Your outbound handler adds the token for any HTTP or HTTPS host; you write the code	Cloud secrets are environment variables the guest can read	Managed credentials proxy for model providers and any HTTPS API; switch a credential to another account
Desktop and browser	Built-in desktop removed in SDK 0.10.2; bring your own	No hosted desktop; a guide shows running your own Chromium	60fps Linux desktop, Chromium and computer use built in
Coding agents	Run Claude Code, Codex, OpenCode or Pi in your image; OpenCode has an SDK helper	Registry images with the Codex CLI and the Harbor eval harness	Seven agents preinstalled, with a prompt, steer and events API
Regions	Several regions across Cloudflare's network	No region choice in the cloud API	EU only (Germany, Finland, France), with EU data residency
Self-hosting	No; the SDK is open source, the platform is not	Open-source smolvm runs on your laptop or your own servers	No, hosted only

Every feature Battleships tracks (43)

Feature	Cloudflare Sandbox	smol machines	boat
Full VM (own kernel)	Yes	Yes	Yes
Docker inside	Yes	Yes	Yes
Nested virtualization	No	No	Yes
Root	Yes	Not published	Yes
Systemd	Not published	Not published	Yes
Desktop GUI	No	No	Yes
Browser	No	No	Yes
Computer-use API	No	No	Yes
SSH	Yes	No	Yes
Persistent disk	No	Yes	Yes
Pause/resume	No	Yes	Yes
Automatic snapshots	No	No	Yes
Fork/clone	No	Yes	Yes
Live fork (no pause)	No	Yes	Yes
Memory fork	No	Yes	No
Custom image (Docker or snapshot)	Yes	Yes	Yes
≥24 h sessions	Yes	Yes	Yes
Idle auto-stop	Yes	Yes	No
Wake on request	Yes	Yes	No
HTTPS preview URLs	Yes	Yes	Yes
Raw TCP inbound	No	Not published	Yes
Public IPv4	No	No	No
Egress allowlist	Yes	Yes	No
Secret proxy	Yes	No	Yes
Secret proxy for any API	Yes	No	Yes
Preinstalled agents	Yes	Yes	Yes
Agent harness API	Yes	No	Yes
MCP server	No	Yes	No
GPU	No	No	No
Windows	No	No	No
Arm64	No	Yes	No
Self-hosting	No	Yes	No
BYOC	No	Yes	No
Open source	Yes	Yes	No
Scoped API keys	Not published	Not published	Yes
Spend limits	No	Yes	Yes
Usage per sandbox (API)	Not published	Yes	Yes
Audit logs	Yes	Not published	No
SSO	Yes	Yes	No
SOC 2	Yes	No	No
HIPAA	Yes	No	No
EU data residency	Yes	No	Yes
Zero data retention	Not published	Not published	Yes

Performance

Cloudflare SandboxNot measured

smol machinesNot measured

boat26.69 runs/s

There is no comparable CPU measurement for Cloudflare Sandbox or smol machines: neither has been run on the StarSling hpc-sandbox-benchmarks test. boat did 26.69 runs per second on that Node.js build-and-test loop at 4 vCPU / 8 GB. smol machines publishes a boot time under 200ms for smolvm, which is a start-time figure, not CPU speed.

Node.js build-and-test loop at 4 vCPU / 8 GB, higher is better. Measured with the open hpc-sandbox-benchmarks suite. Cloudflare Sandbox and smol machines have no published run in this suite yet, so there is no like-for-like number to compare.

Pricing in five scenarios

Each bill is priced from the providers' public price lists by the open Battleships engine, with the cheapest plan that runs the scenario.

Scenario	Cloudflare Sandbox, a month	smol machines, a month	boat, a month
One coding agent, workdays 4 vCPU / 8 GB, 50 GB disk, 8 hours a day, 22 days a month, files kept between days	$39 · Workers Paid · with limits	$25 · Standard	$20 · $20/mo
One agent that never stops 4 vCPU / 8 GB, 50 GB disk, running 24/7 all month	$148 · Workers Paid · with limits	$93 · Standard	$26 · $20/mo
50 agents in parallel 50 machines of 4 vCPU / 8 GB at once, 8-hour sessions, 1,100 sessions a month, Docker inside	$1,660 · Workers Paid · with limits	$1,139 · Pro	$317 · $20/mo × 3 seats
Sandboxes for your users 2 vCPU / 4 GB, 30,000 sessions of 10 minutes a month, up to 300 at once	$476 · Workers Paid	$465 · Startup	$200 · $100/mo × 2 seats
1,000 short jobs at once 2 vCPU / 4 GB, 1,000 at once, 3 minutes each, 200,000 jobs a month	$1,889 · Workers Paid · with limits	$1,389 · Startup	$2,000 · $2000/mo · with limits

Cloudflare Sandbox: You need Workers Paid ($5 a month minimum). CPU is billed only while in use; memory and disk are billed on the instance size you picked until the container sleeps, and 4 vCPU always comes with 12 GiB.

smol machines: smol cloud charges a base fee for every hour a machine runs, plus the CPU and memory the guest actually uses, with a one-minute minimum and disk billed even while stopped. Pro ($20) and Startup ($150) are monthly fees on top of usage, not credit.

smol machines: Plans start at $20 a month, and the whole fee is usage credit, billed per second while a sandbox runs. A stopped sandbox costs nothing and keeps its disk.

Limits in those scenarios

Cloudflare's disk resets after sleep, so the three scenarios that keep 50 GB of files between sessions do not fit without your own snapshot or backup code, and its 1,500 vCPU account cap is short of the 2,000 vCPU the 1,000-job burst needs, though it can be raised. smol machines fits all five scenarios but caps machines by plan (20 on Standard, 100 on Pro, 1,000 on Startup), with stopped machines still holding a slot. boat's limit that bites is starts: on the 1,000-job burst, starts above 90 a minute wait in a queue.

Scenario	Cloudflare Sandbox	smol machines	boat
One coding agent, workdays	missing persistent disk	None that bite	None that bite
One agent that never stops	missing persistent disk	None that bite	None that bite
50 agents in parallel	missing persistent disk	None that bite	None that bite
Sandboxes for your users	None that bite	None that bite	None that bite
1,000 short jobs at once	Workers Paid: max 1,500 vCPU running at once (needs 2,000)	None that bite	max 2,400 starts/day (needs ~6,667) max 600 starts/hour (needs ~1,000) bursts above 90 starts/min are queued (a burst of 333 takes ~4 min to start)

Which one should you use?

Use Cloudflare Sandbox when

your app already runs on Workers and you want short sandboxes that sleep when idle, wake on request, and follow egress rules you write in code.

Egress rules you can program. Teams that must control traffic can block every host not listed and run their own Worker code on each outbound request.
Sleeps when idle, wakes on request. Useful for many short, spiky sessions: a sandbox sleeps when quiet, wakes on the next request, and bills CPU only while busy.
Right next to your Workers app. If your app already runs on Workers, sandboxes sit beside Durable Objects and R2, across several regions of Cloudflare's network.

Use smol machines when

you want one open-source VM engine from your laptop to your own servers, machines that keep their files, or live branches of a running machine.

Open source, laptop to your own servers. Teams that want the same VM locally, in a hosted cloud and on their own servers can use one open-source engine.
Live branches with memory. Useful for RL and test fan-out: branch a running machine with its memory and processes, paying the one-minute minimum once.
Files that survive a stop. Agents that come back to the same work keep their filesystem across a stop, on machines of up to 32 vCPU.

Where boat fits

If your agents work for hours on builds, tests, emulators or a desktop, both Cloudflare Sandbox and smol machines leave pieces for you to build. boat gives each agent a full VM that keeps its disk, runs full Docker with /dev/kvm, streams a desktop, and comes with coding agents you drive from outside.

Files kept, stops free

On Cloudflare a sleeping sandbox wakes with a fresh disk unless your code saves a snapshot, which expires after 30 days. smol machines keeps files but bills the disk while stopped. boat saves the disk every minute and a stopped sandbox costs nothing.

A whole machine, not just a VM boundary

Cloudflare runs Docker with iptables off and has no raw TCP; smol cloud has no SSH, no nested virtualization and 16 published ports. boat has full Docker, /dev/kvm, SSH, 50 HTTPS ports and raw TCP.

Desktop, agents and keys built in

Neither ships a desktop. On Cloudflare you bake agents into your image and write the code that adds each token; on smol cloud secrets sit in the guest, readable by a prompt injection. boat has a 60fps desktop, seven agents and a credentials proxy.

Use boat when your agents do real work for hours: full Docker, emulators, SSH and a desktop, on a machine that keeps its files, with coding agents you drive from outside and keys that never enter the sandbox. Compare it one to one: boat vs Cloudflare Sandbox and boat vs smol machines.

Questions people ask

Is Cloudflare Sandbox cheaper than smol machines?

In all five scenarios on this page, smol machines has the lower estimate, for example $93 a month against $148 for one agent that never stops. For sandboxes for your users they are close, at $465 against $476. Cloudflare also misses three scenarios because its disk resets on sleep.

Which is faster, Cloudflare Sandbox or smol machines?

Neither has a result on the CPU benchmark used here, so there is no fair speed comparison. smol machines publishes a boot time under 200ms for smolvm. boat scored 26.69 runs per second on that benchmark.

Can Cloudflare Sandbox and smol machines run Docker?

Both can. Cloudflare supports docker:dind with iptables and IP forwarding turned off, because containers cannot change iptables. smol machines runs Docker inside the VM with its data on the ext4 disk. boat runs full Docker with root and systemd, plus /dev/kvm.

Which one keeps my files between sessions?

smol machines keeps the filesystem across a stop, though the disk keeps billing. Cloudflare starts from a fresh disk after sleep unless your code saved a snapshot (public beta, kept 30 days) or an R2 backup. boat saves the disk every minute and on stop.

Can either one fork a running sandbox?

smol machines can branch a running machine into children that keep its memory and processes. Cloudflare has no fork; you restore a saved snapshot or backup into a new sandbox. boat forks a running sandbox with its disk.

Can I self-host Cloudflare Sandbox or smol machines?

smol machines, yes: smolvm is open source and runs on macOS, Linux and Windows hosts. Cloudflare's SDK is open source, but the platform it runs on cannot be self-hosted. boat is a hosted service only.

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