Run untrusted agent code in a sandbox you pay for per session

Four requests: create a sandbox on a managed Python image — CPU by default, or a GPU type on request — then exec a command inside it and read stdout, stderr and the exit code, poll its status, and terminate it. Create carries the sandbox price; each of the other three is a small per-operation price.

A short-lived CPU sandbox is the flat rate on the card. A GPU type prices the create call above it by tier, and a lifetime beyond the flat-rate window bills it by the hour for the whole lifetime you requested, up front, with no refund on early terminate — the parameter table below carries the exact window, caps and GPU types the route enforces, and the 402 quotes the exact figure before anything runs.

In Claude Code, Claude Desktop, Cursor, Windsurf, Cline and any other MCP host, this is the blockrun_modal tool of the BlockRun MCP server — the agent calls it like any other tool and the result comes back in the conversation. In OpenClaw, Codex and Hermes, ClawRouter exposes the same catalog. In your own code, the Python and TypeScript SDKs wrap the endpoint above with types; any HTTP client works too. Every harness, with its setup →

No account and no API key stand between an agent and the first call: the request is quoted in dollars and the agent's client pays it. A team that prefers keys gets one, with a monthly invoice.

E2B, Daytona and Modal each sell secure code execution for agents behind an account: a key, a monthly plan or a prepaid balance, and a usage bill at the end. Modal is the runtime behind this page — the same managed images, the same isolation — reached without the account.

Four requests: create a sandbox on a managed Python image, CPU by default or a GPU type on request; exec a command inside it and read stdout, stderr and the exit code; poll its status; terminate it. Create carries the sandbox price, and each of the other three is a small per-operation price, so an agent that runs one snippet pays for one sandbox and a few operations, not a month.

The one thing to know before creating: lifetime is priced up front. A short-lived CPU sandbox is the flat rate on the card; a longer lifetime or a GPU type prices the create call above it, and there is no refund on early terminate. The parameter table above carries the exact window, caps and GPU types the route enforces.