Azure Container Apps Sandboxes vs smol machines

Both give each agent its own microVM with its own kernel and can copy a running machine with its memory. Azure Container Apps Sandboxes lives inside your Azure account with strict outbound rules and 40 regions, while smol machines is an open-source engine that runs the same VM on your laptop, in its hosted cloud or on your own servers.

The companies and products

Azure Container Apps Sandboxes

Azure Container Apps Sandboxes is a service inside Microsoft Azure that gives each agent or user an isolated microVM you create, suspend and resume through an SDK.

It is part of Azure Container Apps, the hyperscaler's serverless container platform, and lives in your Azure subscription as a sandbox group resource. Each sandbox boots from an OCI image or a snapshot, has its own kernel, and can be suspended with its memory and resumed in under a second. It is built for teams already on Azure that want stateful code execution with Azure networking, identity and billing.

Kind of product: A compute type inside Azure Container Apps, next to apps, jobs and dynamic sessions
Isolation: Each sandbox runs in its own secure boundary with its own kernel
Regions: 40 Azure regions, 9 of them in the EU
Sizes: Tiers from 0.25 cores / 0.5 GB to 4 cores / 8 GB; up to 16 vCPU / 32 GB by API
Quota: 500 concurrent active cores and 3,000 API requests a minute by default, raised by support request
Access: Microsoft Entra ID accounts only, with the Container Apps SandboxGroup Data Owner role
Compliance: Azure holds a SOC 2 Type 2 report for its cloud services; the scope list names which services it covers

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. “34th cheapest of 345” means 33 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	Azure Container Apps Sandboxes: 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	288th of 367, with limits $5,276 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	302nd of 366, with limits $6,544 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; smol machines ranks 12th with a one-minute minimum and pay-for-what-the-guest-uses billing, and Azure ranks 34th with memory suspend and sub-second resume.	34th cheapest of 345 $354 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, and both start a stopped machine again on the next request; boat ranks 1st, adding a desktop, hosting on up to 50 ports and a credentials proxy.	22nd cheapest of 361 $2,260 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 Both can copy a running machine with its memory, so many rollouts start from one prepared state; smol machines branches pay the one-minute minimum once rather than per clone.	153rd of 360, with limits $10,740 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 Both fit agent evals; smol machines has a registry image with the Harbor eval harness, and Azure has Copilot CLI and Claude Code images run through exec.	75th cheapest of 364 $1,728 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 Android apps or boots VMs needs nested virtualization, which neither Azure nor smol cloud exposes and boat does through /dev/kvm.	103rd cheapest of 377 $1,046 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 A dev box wants SSH, which neither offers; Azure also bills every running second, so a box left on all month only gets close with a 3-year commitment.	322nd of 368, with limits $262 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 Computer-use agents need a screen; both Azure and smol cloud are headless, while boat streams a Linux desktop at 60fps with computer-use tools.	279th of 369, with limits $1,573 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 Neither ships a managed browser: on Azure you install one in your image, and smol machines has a guide for running your own Chromium.	288th of 367, with limits $795 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	284th of 346, with limits $561 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	239th of 338, with limits $10,956 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	278th of 360, with limits $517 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	Azure Container Apps Sandboxes	smol machines	boat
Isolation	MicroVM per sandbox with its own kernel	libkrun microVM with its own guest kernel	Full VM with its own kernel on dedicated AMD Ryzen 9 9950X hosts
Biggest machine	Tiers up to 4 cores / 8 GB; up to 16 vCPU / 32 GB by API	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
Stop, suspend and wake	Suspend with memory and disk, resume in under a second with processes running; traffic wakes it	Filesystem survives a stop, memory paths are emptied; a command or request starts it again; stopped disk keeps billing	Disk is saved every minute and on stop; a stopped sandbox costs nothing and is started by API
Copy a running machine	Snapshot a running sandbox with its memory and create new sandboxes from it	Branch a running machine with its memory and processes; checkpoints capture RAM to a file	Fork a running sandbox with its disk
Nested virtualization	Not documented	Not exposed in the cloud API; a local smolvm flag only	Yes, /dev/kvm for Android emulators and VMs
Docker inside	Depends on the image: azure-dev ships Docker on systemd; the default ubuntu image has only Buildah	Docker runs inside the VM, with its data on the machine's ext4 disk	Docker, systemd and root on every sandbox
Getting a shell	Interactive shell through the aca CLI, SDK or portal; no SSH	Command API, sessions and a WebSocket terminal capped at one hour per connection; no SSH	SSH, plus a command API and terminal
Inbound access	Public HTTPS routes per published port; private endpoint from your VNet; no public IP	Up to 16 published ports through a returned URL or an authenticated connect route; no dedicated IP	HTTPS URLs for up to 50 ports, token-protected by default; raw TCP; dedicated IPv4 or IPv6
Outbound rules	Allow, deny, rewrite and header rules by host, path and method; VNet integration	Blocked, open, or an allowlist of hosts and CIDR ranges	Open internet, no provider-side allowlist
Desktop, browser and computer use	Headless; no desktop or managed browser	No hosted desktop; a guide shows running your own Chromium	Linux desktop streamed at 60fps, Chromium and computer-use tools preinstalled
Coding agents	Copilot CLI and Claude Code images, run through the exec API	Registry images with the Codex CLI and the Harbor eval harness, run through the command API	Seven agents preinstalled, with a prompt, steer and events API
Keeping API keys out of the sandbox	Group secrets usable in egress header rules; Copilot and Anthropic tokens are injected into the sandbox at startup	Cloud secrets are environment variables the guest can read; key swapping only in self-hosted smolvm	Credentials proxy for model providers and any HTTPS API; switch a credential to another account when credits run out
Regions	40 Azure regions, 9 of them in the EU	No region choice in the cloud API	EU only (Germany, Finland, France), with EU data residency
Self-hosting	No; runs only inside an Azure subscription	Open-source smolvm runs on your laptop or your own servers with the same .smolmachine artifact	No; hosted service

Every feature Battleships tracks (43)

Feature	Azure Container Apps Sandboxes	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	Yes	Not published	Yes
Desktop GUI	No	No	Yes
Browser	No	No	Yes
Computer-use API	No	No	Yes
SSH	No	No	Yes
Persistent disk	Yes	Yes	Yes
Pause/resume	Yes	Yes	Yes
Automatic snapshots	Yes	No	Yes
Fork/clone	Yes	Yes	Yes
Live fork (no pause)	Yes	Yes	Yes
Memory fork	Yes	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	No	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	No	Yes	No
Scoped API keys	Not published	Not published	Yes
Spend limits	Yes	Yes	Yes
Usage per sandbox (API)	Yes	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

Azure Container Apps SandboxesNot measured

smol machinesNot measured

boat26.69 runs/s

Neither Azure Container Apps Sandboxes nor smol cloud has a comparable CPU measurement yet, so this page makes no speed claim between them. boat did 26.69 runs per second on the StarSling hpc-sandbox-benchmarks 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. Azure Container Apps Sandboxes 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	Azure Container Apps Sandboxes, 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	$68 · Pay-as-you-go	$25 · Standard	$20 · $20/mo
One agent that never stops 4 vCPU / 8 GB, 50 GB disk, running 24/7 all month	$262 · Pay-as-you-go · 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	$3,421 · Pay-as-you-go	$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	$989 · Pay-as-you-go	$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	$2,148 · Pay-as-you-go	$1,389 · Startup	$2,000 · $2000/mo · with limits

Azure Container Apps Sandboxes: Azure bills per second on the Container Apps Consumption meters for the vCPU and memory of the sandbox's tier while it runs, including idle time before auto-suspend (5 minutes by default). There is no plan fee, stopped sandboxes pay no CPU or memory, and some regions such as West Europe charge more.

smol machines: smol cloud charges $0.04 for every hour a machine runs plus $0.05 per active vCPU-hour and $0.0162 per active GB-hour of memory, with a one-minute minimum and disk billed even while stopped. Pro ($20 a month) and Startup ($150 a month) are fees on top of usage, not credit.

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

Limits in those scenarios

Azure has no session cap, but it bills a running sandbox every second, so one agent that never stops only gets close with a 3-year commitment. Azure's default quota is 500 active cores, raised by support request, and Docker inside means picking an image like azure-dev. smol machines caps machines by plan, 20 on Standard, 100 on Pro and 1,000 on Startup, with stopped machines still holding a slot, so 50 agents needs Pro and 1,000 short jobs at once needs Startup. boat's tighter limit is starts: at 1,000 short jobs at once its $2,000 plan queues starts above 90 a minute.

Scenario	Azure Container Apps Sandboxes	smol machines	boat
One coding agent, workdays	None that bite	None that bite	None that bite
One agent that never stops	3-year commitment	None that bite	None that bite
50 agents in parallel	None that bite	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	None that bite	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 Azure Container Apps Sandboxes when

your team already runs on Azure and wants sandboxes that suspend with their memory, wake on traffic, sit behind per-request egress rules, or run in a region outside the EU.

Memory suspend and wake on traffic. For stateful jobs that sleep between requests: a sandbox suspends with its memory and resumes in under a second with processes running.
Fine-grained outbound rules. Its egress policy can allow, deny or rewrite each outbound request by host, path and method, and join your Azure VNets.
Inside Azure, in 40 regions. Teams already on Azure get Entra ID sign-in, Azure billing and their own networks, in 40 regions around the world.

Use smol machines when

you want one open-source VM engine from your laptop to your own servers, fan out many branches of a running machine, or need arm64 or 32 vCPU machines.

Open source, laptop to your own servers. One open-source engine, smolvm, runs the same machine on your laptop, in smol cloud or on servers you run yourself.
Live branches that pay once. Branch a running machine with its memory and processes, and the one-minute minimum is paid once, not per clone.
Bigger machines and arm64. Startup machines go up to 32 vCPU / 32 GB, and registry images come in both amd64 and arm64.

Where boat fits

Azure Container Apps Sandboxes and smol machines are both good at short, stateful microVMs that sleep and wake. If your agents instead work for hours like a person at a computer, installing tools, running emulators, using a browser and serving apps, boat gives each one a whole machine with that built in.

A whole computer you can SSH into

Neither Azure nor smol cloud offers SSH or exposes /dev/kvm, so an agent cannot start an Android emulator or a VM, and SSH tools must be rewired to an exec API. boat has both, plus raw TCP and 50 HTTPS ports.

A screen and a browser for every agent

Both are headless: for a computer-use agent you build, package and maintain a browser, a virtual display and a stream in your own image. boat streams a Linux desktop at 60fps with Chromium and computer use ready.

Agents you drive from outside, keys kept outside

On both, coding agents run through raw exec calls, and model tokens or secrets sit inside the sandbox where a prompt injection can read them. boat drives seven agents inside from outside by API, and real keys stay in a credentials proxy.

Use boat when your agents need a whole computer for real work: SSH, Docker, emulators, a desktop and a browser, with coding agents you drive from outside and keys that never enter the sandbox. Compare it one to one: boat vs Azure Container Apps Sandboxes and boat vs smol machines.

Questions people ask

Is Azure Container Apps Sandboxes cheaper than smol machines?

No, smol machines costs less in all five scenarios on this page, for example $68 vs $25 a month for one coding agent on workdays. Azure bills the full tier while a sandbox runs, while smol bills the CPU and memory the guest actually uses plus a base fee per running hour.

Which is faster, Azure Container Apps Sandboxes or smol machines?

Neither has been measured on the same CPU test yet, so there is no fair answer. boat did 26.69 runs per second on the StarSling Node.js build-and-test loop at 4 vCPU / 8 GB.

Can I run Docker in Azure Container Apps Sandboxes and smol machines?

Yes on both, with care. Azure's azure-dev image ships Docker on systemd, while the default ubuntu image has only Buildah; smol says Docker data must live on the machine's ext4 disk. boat runs Docker on every sandbox and also exposes /dev/kvm for emulators and VMs.

Can I SSH into either one?

No. Azure gives a shell through the aca CLI, SDK or portal, and smol cloud gives a command API and a WebSocket terminal capped at one hour per connection. Every boat sandbox has an SSH endpoint.

Can I self-host smol machines or Azure Container Apps Sandboxes?

smol machines, yes: the smolvm engine is open source and runs on macOS, Linux and Windows hosts. Azure Container Apps Sandboxes runs only inside an Azure subscription, and boat is a hosted service only.

Do they keep API keys out of the sandbox?

Not fully. Azure can use group secrets in egress header rules, but its Copilot and Anthropic tokens are injected into the sandbox at startup, and smol cloud secrets are plaintext inside the guest. boat's credentials proxy keeps real keys outside for model providers and any HTTPS API.

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