Runtime vs CodeSandbox

Runtime runs agent code in Firecracker microVMs, like the CodeSandbox SDK, and costs 74% less for an agent that mostly waits on a model.

The saving: 1,000 one-minute runs of a 2 vCPU, 4 GiB sandbox cost $0.64 on Runtime and $2.48 on CodeSandbox. At 100,000 runs a month that is $63.89 against $247.67, $184 a month saved.

Where Runtime is better

• You pay for the CPU you use. CodeSandbox bills a VM's size in credits for as long as it runs. Runtime measures the CPU your code actually uses, so time spent waiting on a model costs only a small floor, a twentieth of a vCPU.
• Cheaper even when busy. With both CPUs working the whole time, the example job costs $1.33 on Runtime and $2.48 on CodeSandbox.
• Billed by the second. CodeSandbox rounds each VM's runtime up to the next minute. Runtime compute has no one-minute minimum.
• Any shape. CodeSandbox sells fixed VM sizes. On Runtime you choose vCPUs and memory for each sandbox and pay for no more.
• No plan fee for concurrency. More than 10 VMs at once on CodeSandbox needs the $170-a-month Scale plan. Runtime has no plan: a paid account starts at 100 sandboxes at once and raises the limit on request.
• Your agent sets itself up. It runs npx withruntime sandbox run --trial -- ..., shows you a link, and starts once you approve in the browser. No API key goes into a prompt or a config file, and the MCP server reuses the same connection.

At a glance

CodeSandbox's figures come from the Together Code Sandbox documentation, which covers the CodeSandbox SDK, checked 23 September 2026.

	Runtime	CodeSandbox SDK
Isolation	Firecracker microVM, own kernel	Firecracker microVM
CPU billing	$0.025 per vCPU-hour of measured CPU, with a small floor	By VM size: Nano (2 cores, 4 GB) is $0.1486 an hour
Memory billing	$0.0075 per reserved GiB-hour	Inside the VM size
Billing unit	By the second	By the minute, rounded up
Plan fee	None; prepaid credit from $10	Build free with 10 VMs at once; Scale $170 a month
Free start	50 sandbox hours, no card	The free Build plan
Snapshots, forks	Files, memory and running processes	Memory snapshot and restore

Cost for the same job

Take 1,000 runs of a 2 vCPU, 4 GiB sandbox. Each run lasts 60 seconds and keeps the CPU busy for 20 CPU-seconds: an agent that spends most of its time waiting for a model. On CodeSandbox that is a Nano VM, 10 credits an hour at $0.01486 a credit.

TextRuntime      CPU    1,000 × 20 s / 3,600 × $0.025      = $0.14             Memory 1,000 × 60 s / 3,600 × 4 × $0.0075 = $0.50             Total                                        $0.64CodeSandbox  Size   1,000 × 60 s / 3,600 × $0.1486     = $2.48

• Saving: 74%, or $1.84 per 1,000 runs.
• Per month: at 100,000 runs, $63.89 on Runtime against $247.67 on CodeSandbox.
• Busier work: with both CPUs busy for the whole minute, $1.33 on Runtime against $2.48 on CodeSandbox.

Each run here is a whole minute, so CodeSandbox's rounding adds nothing; a 40-second run would still be billed as a minute there. Plan fees, storage, network and taxes are left out of both. See pricing for Runtime's terms.

How to switch

Give your coding agent the one instruction in migration. It replaces the CodeSandbox calls on a branch, tests them on the free trial, and tells you what you save each month. Your old code stays on the main branch until you merge.

Runtime:

TypeScriptimport { Sandbox } from "withruntime";const box = await Sandbox.create({ funding: "trial" });try {  console.log((await box.exec("python3 -c 'print(6 * 7)'", { check: true })).stdout);} finally {  await box.stop();}

When CodeSandbox may fit better

• Very large machines. CodeSandbox VMs go up to 64 cores and 128 GB.
• Many VMs on a plan. The Scale plan runs 250 VMs at once.

Sources

Checked 23 September 2026. The rates are from Together's documentation of the CodeSandbox SDK; CodeSandbox is a Together company.

• Together Code Sandbox
• CodeSandbox SDK pricing
• Runtime pricing, security and products