Runtime vs AWS Lambda MicroVMs

Runtime runs agent code in Firecracker microVMs, like Lambda MicroVMs, and costs 85% 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 $4.20 on Lambda MicroVMs. At 100,000 runs a month that is $63.89 against $420.33, $356 a month saved, with no AWS account, IAM role or VPC to set up first.

Where Runtime is better

• You pay for the CPU you use. Lambda MicroVMs bill the baseline vCPUs and memory for every second a MicroVM runs, busy or not. 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.
• Lower rates on both meters. $0.025 per vCPU-hour against about $0.0997, and $0.0075 per GiB-hour of memory against about $0.0132 per GB-hour. With both CPUs busy the whole time, the example job still costs $1.33 on Runtime and $4.20 on Lambda MicroVMs.
• Bigger sandboxes. A paid Runtime sandbox takes up to 16 vCPUs and 64 GiB, with memory chosen apart from CPU. A MicroVM's baseline tops out at 4 vCPUs and 8 GB, always 2 GB per vCPU.
• Sessions that last. A MicroVM keeps its state for up to 8 hours. A Runtime sandbox runs as long as you extend its lease, or stays up with persistent: true, and a paused one keeps its memory for 1 to 365 days.
• Fork a running machine. A Runtime fork copies a sandbox as it is now, memory and processes included, into up to 10 running copies.
• 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 access key goes into a prompt or a config file, and the MCP server reuses the same connection.
• Guardrails for agents. Read-only keys, a daily spending limit per key and maxCostMicros on each create keep an agent inside its budget, and every write takes an idempotency key.

At a glance

Lambda MicroVMs' figures come from AWS's public pricing and product pages, checked 25 September 2026. Rates are for Arm (Graviton) in US East (N. Virginia).

	Runtime	AWS Lambda MicroVMs
Isolation	Firecracker microVM, own kernel	Firecracker microVM
CPU billing	$0.025 per vCPU-hour of measured CPU, with a small floor	$0.0000276944 per baseline vCPU-second while running
Memory billing	$0.0075 per reserved GiB-hour	$0.0000036667 per baseline GB-second while running
Sizes	Up to 16 vCPUs and 64 GiB paid, chosen apart	Baseline up to 4 vCPUs and 8 GB, 2 GB per vCPU
Session length	Leases extended as needed, or persistent	State kept up to 8 hours
Suspend	Files, memory and processes, kept 1 to 365 days	Memory and disk in a snapshot, at $0.08 per GB-month
Free start	100 sandbox hours, no card	No free tier for MicroVMs
Plan fee	None; prepaid credit from $10	None; an AWS account
Agent sign-in	Browser approval; no key in the agent's config	AWS credentials and IAM

Cost for the same job

Take 1,000 runs of a 2 vCPU, 4 GiB sandbox (a 2 vCPU, 4 GB baseline on Lambda MicroVMs). 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.

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                                                   $0.64Lambda   CPU    1,000 × 60 s × 2 × $0.0000276944              = $3.32         Memory 1,000 × 60 s × 4 × $0.0000036667              = $0.88         Total                                                   $4.20

• Saving: 85%, or $3.56 per 1,000 runs.
• Per month: at 100,000 runs, $63.89 on Runtime against $420.33 on Lambda MicroVMs.
• Busier work: with both CPUs busy for the whole minute, $1.33 on Runtime against $4.20 on Lambda. At this size Runtime is cheaper however busy the sandbox is.

Snapshot storage and its reads and writes, data transfer, taxes and credits 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 MicroVM 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.

A MicroVM image built from a container image maps to a custom image built from the same Dockerfile, and a MicroVM's HTTPS endpoint maps to a preview:

TypeScriptimport { Sandbox } from "withruntime";const box = await Sandbox.create({ funding: "trial" });try {  await box.spawn("python3 -m http.server 8080");  const preview = await box.previews.create(8080);  console.log(preview.urlWithToken);} finally {  await box.stop();}

When Lambda MicroVMs may fit better

• Everything else is on AWS. A MicroVM reaches your VPC through the Lambda Network Connector and is governed by the IAM policies you already run.
• Many regions. AWS runs Lambda in regions worldwide. Runtime runs in one US region.
• Arm code. MicroVMs run on Graviton. Runtime sandboxes are x86-64.

Sources

Checked 25 September 2026.

• AWS Lambda pricing
• Lambda MicroVMs
• Announcing Lambda MicroVMs
• Runtime pricing, security and products