CodeSandbox SDK vs Replit
CodeSandbox SDK is a sandbox API: your code starts Firecracker VMs that hibernate with their memory and wake on the next request. Replit is an AI app builder: you describe an app, Replit Agent writes it, and Replit hosts it.
The companies and products
CodeSandbox SDK
CodeSandbox SDK is an API from CodeSandbox, now a Together AI company, that starts sandboxed development VMs on the same infrastructure as the CodeSandbox editor.
Each sandbox is a Firecracker microVM built from a template or any Dockerfile. When it goes idle it hibernates with a memory snapshot, and it resumes or forks from that snapshot in seconds. You drive it from a TypeScript SDK through terminals, commands, files and HTTPS hosts. Together's docs now call it the legacy offering and point new users to its successor, the together-sandbox SDK.
Replit
Replit is an AI app builder and hosting platform: you describe an app in chat, Replit Agent writes it, and Replit publishes it.
You work in a browser workspace where Replit Agent sets up the project, writes the code, tests it and fixes problems, with system packages managed by Nix. When the app is ready you publish it as an Autoscale, Static, Scheduled or Reserved VM deployment, with Postgres and object storage next to it. It is built for people and teams who want a working app, not for programs that need to create many machines by API, so this page compares the parts where the two overlap.
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. “46th cheapest of 345” means 45 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 | CodeSandbox SDK: price rank | Replit: price rank | boat: price rank |
|---|---|---|---|
| Software factory 100 at once · 4 vCPU / 8 GB · 2,200 sessions of 8 h a month A software factory starts and steers many agents from code; CodeSandbox SDK gives you the VMs but no agents, and Replit's MCP server drives Replit Agent one app at a time. | 178th of 367, with limits $1,939 a month | 181st of 367, with limits $2,000 a month | 3rd cheapest of 367 $634 a month |
| Always-on AI employees 50 machines 24/7 · 2 vCPU / 4 GB | 215th of 366, with limits $2,478 a month | 202nd of 366, with limits $2,033 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 CodeSandbox SDK is a full fit here, with VMs that hibernate with their memory and wake on the next request; Replit's Autoscale is lower at $146 a month but it is a web host, not a code runner. | 46th cheapest of 345 $642 a month | 228th of 345, with limits $146 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 CodeSandbox SDK caps Scale at 250 VMs at once and Replit does not publish its limit, so 300 user sandboxes fit neither as is; boat ranks 1st here. | 140th of 361, with limits $1,707 a month | 233rd of 361, with limits $825 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 CodeSandbox SDK's memory forks let many rollouts branch from the same running state, which Replit does not offer. | 348th of 360, with limits $3,861 a month | 258th of 360, with limits $4,226 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 CodeSandbox SDK fits agent evals because your code can start and fork many VMs, while Replit has no API to start many machines; boat ranks 10th with full VMs. | 64th cheapest of 364 $1,335 a month | 265th of 364, with limits $685 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 jobs that build containers need Docker, which CodeSandbox SDK has and Replit's Nix-based environments do not document; boat also adds /dev/kvm for Android and VM builds. | 92nd cheapest of 377 $860 a month | 275th of 377, with limits $425 a month | 4th cheapest of 377 $86 a month |
| 24/7 dev boxes 1 machine 24/7 · 4 vCPU / 8 GB A Replit workspace is a good place to code by hand, and a CodeSandbox SDK VM bills every minute it runs; boat gives a full VM with SSH, Docker and systemd that costs nothing when stopped. | 310th of 368, with limits $240 a month | 165th of 368, with limits $109 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 has a computer-use API: CodeSandbox SDK has no desktop and Replit's VNC pane shows a desktop to a person, while boat streams one at 60fps to agents. | 206th of 369, with limits $691 a month | 190th of 369, with limits $619 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 | 251st of 367, with limits $443 a month | 229th of 367, with limits $317 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 | 281st of 346, with limits $508 a month | 234th of 346, with limits $217 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 | 193rd of 338, with limits $7,390 a month | 150th of 338, with limits $4,378 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 | 240th of 360, with limits $326 a month | 208th of 360, with limits $215 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 | CodeSandbox SDK | Replit | boat |
|---|---|---|---|
| Kind of product | Sandbox API: Firecracker VMs you start from a TypeScript SDK | AI app builder with browser workspaces and app hosting | Sandboxes you create, stop and fork by API, SDK or CLI |
| Isolation | Firecracker microVM with its own kernel | Not documented; the security page says strong logical separation between users | Full VM with its own kernel on dedicated AMD Ryzen 9 9950X hosts |
| Creating machines from code | SDK creates, forks and hibernates sandboxes; 1,000 new sandboxes an hour on Scale | MCP server tools to create, update and publish apps; no API to start many machines | API, SDK and CLI to create, stop, resume and fork many sandboxes |
| Machines at once | 250 VMs at once on Scale; more on Enterprise | Not published | 300 at once fits on two $100 seats; bursts above 90 starts a minute are queued |
| Pause and resume | Hibernates with a memory snapshot; resumes with processes still running | Workspace files and Agent checkpoints; a Reserved VM runs continuously | Disk saved every minute and on stop; resume boots the machine again |
| Wake on request | Yes; an HTTP request to a host wakes a hibernated VM | Autoscale starts on the first request and goes idle after 15 minutes | No; a stopped sandbox is started by API |
| Docker and nested virtualization | Docker and root, built from any Dockerfile; nested virtualization not documented | System packages come from Nix; the docs do not describe Docker, systemd or /dev/kvm | Docker, root, systemd and /dev/kvm on every machine |
| Shell access | Terminals, commands and files through the SDK; no SSH | SSH into the workspace on paid plans | SSH, plus exec and files over the API |
| Inbound access | HTTPS host per port, public by default, signed tokens for private hosts; no raw TCP or public IP | Published apps on HTTPS domains, custom domains and private deployments | HTTPS URLs for up to 50 ports, token-protected by default; raw TCP; a dedicated IPv6 or IPv4 |
| Desktop and computer use | No desktop; a headless Chromium template | VNC pane that streams a native desktop to your browser; no computer-use API | Linux desktop streamed at 60fps, Chromium and computer-use tools |
| Coding agents | Run your own agent through the command API | Replit Agent, which you can also drive from an MCP client | Claude Code, Codex, OpenCode and more preinstalled, with a prompt, steer and events API |
| Keeping keys out of the sandbox | Secrets passed in as environment variables | Replit manages keys for OpenAI, Anthropic, Google and OpenRouter models; other keys are secrets in the app | Credentials proxy for model providers and any HTTPS API; switch a credential to another account when credits run out |
| Regions | No region choice; a country hint steers scheduling but is not guaranteed | North America, Europe, Asia, South America and Australia for published apps on Core and up | EU only: Germany, Finland, France |
Every feature Battleships tracks (43)
| Feature | CodeSandbox SDK | Replit | boat |
|---|---|---|---|
| Full VM (own kernel) | Yes | Yes | Yes |
| Docker inside | Yes | No | Yes |
| Nested virtualization | No | No | Yes |
| Root | Yes | Not published | Yes |
| Systemd | Not published | No | Yes |
| Desktop GUI | No | Yes | Yes |
| Browser | No | No | Yes |
| Computer-use API | No | No | Yes |
| SSH | No | Yes | Yes |
| Persistent disk | Yes | Yes | Yes |
| Pause/resume | Yes | No | Yes |
| Automatic snapshots | Yes | Yes | Yes |
| Fork/clone | Yes | Yes | Yes |
| Live fork (no pause) | Yes | No | Yes |
| Memory fork | Yes | No | 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 | No | No | No |
| Secret proxy | No | Yes | Yes |
| Secret proxy for any API | No | No | Yes |
| Preinstalled agents | No | Yes | Yes |
| Agent harness API | No | Yes | Yes |
| MCP server | No | Yes | No |
| GPU | No | No | No |
| Windows | No | No | No |
| Arm64 | No | Not published | No |
| Self-hosting | No | No | No |
| BYOC | No | No | No |
| Open source | No | No | No |
| Scoped API keys | Not published | Not published | Yes |
| Spend limits | Not published | Yes | Yes |
| Usage per sandbox (API) | No | Yes | Yes |
| Audit logs | Not published | Yes | No |
| SSO | Yes | Yes | No |
| SOC 2 | Yes | Yes | No |
| HIPAA | No | No | No |
| EU data residency | No | Yes | Yes |
| Zero data retention | Not published | Not published | Yes |
Performance
Neither CodeSandbox SDK nor Replit has a comparable CPU measurement, so we cannot say which of the two is faster. boat did 26.69 runs per second on StarSling's hpc-sandbox-benchmarks Node.js loop at 4 vCPU / 8 GB, on dedicated AMD Ryzen 9 9950X hosts, and neither of the other two was part of that run.
Node.js build-and-test loop at 4 vCPU / 8 GB, higher is better. Measured with the open hpc-sandbox-benchmarks suite. CodeSandbox SDK and Replit 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 | CodeSandbox SDK, a month | Replit, 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 | $193 · Scale | $122 · Pro $100 (annual) · with limits | $20 · $20/mo |
| One agent that never stops 4 vCPU / 8 GB, 50 GB disk, running 24/7 all month | $341 · Scale | $122 · Pro $100 (annual) · with limits | $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 | $2,500 · Scale | $1,330 · Pro $1,000 (annual) · with limits | $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 | $815 · Scale · with limits | $403 · Pro $250 (annual) · with limits | $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 | $1,632 · Scale · with limits | $825 · Pro $1,000 (annual) · with limits | $2,000 · $2000/mo · with limits |
CodeSandbox SDK: You buy VM credits and each size burns a fixed number per hour, billed per started minute while the VM runs, including idle time before it hibernates. Scale adds a $170 monthly platform fee that is not usage credit, and a hibernated VM costs nothing.
Replit: Plans (Core $20, Pro from $100) turn into monthly credits for Agent work and hosting, then usage goes to pay-as-you-go. A Reserved VM has a fixed monthly price per size and bills whether busy or idle, so our prices treat each agent as one Reserved VM and leave out Agent usage.
Replit: Plans start at $20 a month, and the whole fee is usage credit spent per second while a sandbox runs. A stopped sandbox costs nothing and keeps its disk.
Limits in those scenarios
CodeSandbox SDK's Scale plan allows 250 VMs at once, so 300 sandboxes for your users and 1,000 short jobs at once do not fit without Enterprise; each VM has a 20 GB disk, and prices for more disk and for egress are not published. Replit is marked as not a fit in every scenario because one Reserved VM is one published app that runs all month, it does not publish how many can run at once, and it does not document Docker. On boat, the 1,000-job burst is queued above 90 starts a minute and needs more starts per day than the $2,000 plan allows.
| Scenario | CodeSandbox SDK | Replit | boat |
|---|---|---|---|
| One coding agent, workdays |
|
| None that bite |
| One agent that never stops |
|
| None that bite |
| 50 agents in parallel |
|
| None that bite |
| Sandboxes for your users |
|
| None that bite |
| 1,000 short jobs at once |
|
|
|
Which one should you use?
Use CodeSandbox SDK when
your code needs to start many VMs that sleep between visits and wake on the next HTTP request with their memory intact, and you are fine building on what Together now calls its legacy SDK.
- Built to start machines from code. Good for programs that need many VMs: the SDK creates and forks sandboxes, up to 1,000 new ones an hour on Scale.
- Memory hibernation and wake on request. Useful for sandboxes that sleep between visits: an HTTP request wakes a hibernated VM with its processes still running.
- Forks that share memory. Good for branching many runs from one warm state, such as rollouts or test variants.
Use Replit when
you want Replit Agent to build a web app from a description and host it for you, with databases, hosting that sleeps when idle, or regions outside Europe.
- An app built and hosted for you. Useful if you want a working app from a description: Replit Agent builds, tests and publishes it with Postgres and storage.
- Hosting that costs nothing when idle. Useful for web apps with uneven traffic: Autoscale wakes on the first request and costs nothing while idle.
- Regions on five continents. Useful if your users are spread out: Replit publishes apps in North America, Europe, Asia, South America and Australia.
Where boat fits
If what you are really choosing is a place for AI agents to work for hours, boat gives each one a full VM with SSH, Docker, systemd and /dev/kvm, with the agents, a desktop and a keys proxy already set up. CodeSandbox SDK gives you VMs but leaves the rest to you, and Replit is built around its own agent and published apps rather than machines your code starts.
A whole machine for the agent's tools
CodeSandbox SDK runs Docker but has no SSH and no documented /dev/kvm, and Replit's Nix setup does not describe Docker or systemd. Emulator builds and VM-based tests cannot start on either.
Agents and keys built in
On CodeSandbox SDK you build the agent harness yourself and pass keys in as environment variables. Replit's MCP server drives Replit Agent only, and keys other than AI models sit in the app where the agent's code can read them.
A desktop and open ports for agents
Neither gives an agent a desktop it can drive: CodeSandbox SDK has none and Replit's VNC pane is for a person. Both serve HTTPS only, so databases or game servers an agent starts cannot take raw TCP.
Use boat when your agents do real work for hours: installs, builds, Docker, emulators, a browser and servers other people reach, on a full machine with the agent and its keys already set up. Compare it one to one: boat vs CodeSandbox SDK and boat vs Replit.
Questions people ask
Is CodeSandbox SDK cheaper than Replit?
In our scenarios Replit comes out lower, for example $122 against $193 a month for one coding agent on workdays, and $1,330 against $2,500 for 50 agents. But Replit is marked as not a fit in each one, because it prices an agent as a Reserved VM app that runs all month. boat comes to $20 and $317 for the same two.
Which is faster, CodeSandbox SDK or Replit?
We cannot say. Neither is in the StarSling CPU benchmark we use, so there is no comparable number for either. boat did 26.69 runs per second in that benchmark at 4 vCPU / 8 GB.
Can CodeSandbox SDK or Replit run Docker?
CodeSandbox SDK runs Docker with root inside each VM, and you can build a sandbox from any Dockerfile. Replit sets up environments with Nix packages and its docs do not describe running Docker. Every boat sandbox has Docker, systemd and /dev/kvm.
Can I start many Replit machines from my own code?
Not like a sandbox API. Replit's MCP server lets an MCP client create, update and publish apps through Replit Agent, but there is no API to start many machines. CodeSandbox SDK and boat both create and fork sandboxes from code.
Is CodeSandbox SDK still maintained?
CodeSandbox is now part of Together AI. Together's docs call the CodeSandbox-based SDK deprecated and name together-sandbox as its successor, while self-serve sign-up still runs through CodeSandbox.
Where do they run?
CodeSandbox SDK has no region choice, only a country hint that is not guaranteed. Replit hosts data mainly on Google Cloud in the United States and publishes apps on five continents on Core and up. boat runs only in the EU, in Germany, Finland and France.
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