# Best sandbox for the Vercel AI SDK in 2027 Runtime Cloud (withruntime.com) connects to the AI SDK as tools and costs 66% less than Vercel Sandbox. ## Which sandbox is best for the Vercel AI SDK? It depends on whether the model needs a real machine. For chat turns that mostly wait on the model, Runtime costs least: $53.47 a month for the turns priced below, against $159.11 on Vercel Sandbox and $276.00 on E2B, with any model. Pick just-bash if text tools over your app's own files are enough, a hosted code tool if you stay with OpenAI or Anthropic, or Vercel Sandbox for the SDK's built-in tools. ## How does the AI SDK connect an agent to a sandbox? The SDK runs tools in your own process unless a tool sends the work elsewhere. Its [tools registry](https://ai-sdk.dev/tools-registry) and [harness docs](https://ai-sdk.dev/docs/ai-sdk-harnesses/harness-agent) list these ways to run code: | Route | Where code runs | Models | | ------------------------------------------- | -------------------------------- | ------ | | `@ai-sdk/sandbox-just-bash` | A simulated bash in your process | Any | | `openai.tools.codeInterpreter()` | OpenAI's hosted container | OpenAI | | `anthropic.tools.codeExecution_20260120` | Anthropic's hosted container | Claude | | `code-execution`, `bash-tool`, Vercel's own | Vercel Sandbox | Any | | `bedrock-agentcore` | AWS Bedrock's code interpreter | Any | just-bash describes itself as "a simulated bash environment with virtual filesystem", so it cannot install a package or run a real binary. A provider's own code tool ties the agent to that provider's models. ## What matters in a sandbox for the AI SDK? - **Any model.** Tools that are ordinary AI SDK tools let Claude, GPT, Gemini and open models through the AI Gateway all use the same sandbox. - **A real machine.** A full Linux system where `pip install` and `npm install` work when the model needs more. - **Chat sessions that cost nothing while idle.** Each conversation can keep one sandbox that pauses between turns and wakes with its files, memory and processes. - **Streaming routes.** `streamText` keeps the same tools; stop the sandbox in `onFinish`, and a time limit stops it if the client disconnects. - **Harness agents too.** The SDK's `HarnessAgent` takes a sandbox adapter, with ports for bridge harnesses such as Claude Code and Codex. ## What does an AI SDK chat app cost per month? Fifty thousand chat turns, each two minutes on a 2 vCPU, 4 GiB sandbox and busy for 10 CPU-seconds, at each provider's published rates: | Provider | Isolation | CPU billed on | A month of turns | | -------------- | ----------------------- | ----------------- | --------------------------------- | | Runtime Cloud | Firecracker microVM | Measured use | $53.47 | | Vercel Sandbox | Firecracker microVM | Measured use | $159.11 | | E2B | Firecracker microVM | Every vCPU held | $276.00 | | Daytona | Containers by default | Every vCPU held | $276.00 | | Modal | gVisor, a shared kernel | The CPU requested | $396.60 | ## When might another sandbox fit better? - **No sandbox at all.** If the model only needs shell-like text tools over files your app already holds, just-bash runs in your process with nothing to create. ## Runtime Cloud With Runtime an AI SDK agent gets a full Linux microVM from one line, `tools: runtimeTools(sbx)`, with any model the SDK can call. The four tools run commands and read, write and list files in a Firecracker microVM with its own kernel. They are plain AI SDK tools, so changing models is a one-word change. The same machine is also a sandbox for the SDK's `HarnessAgent`: `createRuntimeSandbox()` from `withruntime/ai-harness`, with ports for bridge harnesses such as Claude Code and Codex ([guide](/docs/vercel-ai-sdk)). - **The machine.** Ubuntu 24.04 with `sudo`, Python, Node.js, Bun and gcc, where pandas, NumPy and matplotlib are already installed. - **Chat sessions.** `Sandbox.getOrCreate("chat-42")` gives each conversation one named sandbox that pauses itself after 300 seconds with nothing happening and wakes on the next turn. - **Cost.** CPU is billed on measured use. The fifty thousand turns above cost $53.47 on Runtime, 66% less than Vercel Sandbox and 81% less than E2B, at rates checked 25 October 2026. ### A run on Runtime, recorded 2 October 2026 ```ts check import { generateText, stepCountIs } from "ai"; import { Sandbox } from "withruntime"; import { runtimeTools } from "withruntime/ai"; await using sbx = await Sandbox.create(); const { text } = await generateText({ model: "anthropic/claude-sonnet-4.6", tools: runtimeTools(sbx), stopWhen: stepCountIs(10), prompt: "Print the first 15 Fibonacci numbers with Node.", }); console.log(text); ``` We ran this `generateText` loop with `ai` 7.0.87 and the SDK's mock model in place of Claude, so the model's two tool calls were scripted and the AI SDK ran them against a live sandbox: ```text runtime_write_file fib.mjs Wrote 132 bytes to /workspace/fib.mjs runtime_exec node fib.mjs && node --version exitCode 0 0 1 1 2 3 5 8 13 21 34 55 89 144 233 377 v24.21.0 ``` Node.js 24 was there with nothing installed first. Streaming routes, chat sessions and spending limits are in [code execution for the AI SDK](/integrations/vercel-ai-sdk). Try it free after `npx withruntime login`. An app that already calls another sandbox moves over with the [migration guide](/docs/migrate). ## Sources Checked 25 October 2026. - [AI SDK tools registry](https://ai-sdk.dev/tools-registry): the code execution and sandbox tools and where each runs - [AI SDK HarnessAgent](https://ai-sdk.dev/docs/ai-sdk-harnesses/harness-agent): the sandbox adapters and what bridge harnesses need - [just-bash](https://github.com/vercel-labs/just-bash): its own description - Each provider's published rates, checked 25 October 2026, as the [pricing guide](/docs/pricing) lists them - The recorded run: Runtime's TypeScript SDK with `ai` 7.0.87's `MockLanguageModelV4`, against production on 2 October 2026