What is the best AI agent sandbox in 2026?

It depends on how your agent spends its time. For code-interpreter tools and short tasks, E2B (Firecracker microVMs, ~150 ms start, $0.0504/vCPU-h + $0.0162/GiB-h) is the default. For long-lived per-user agents that mostly wait on a model, active-CPU billers win: Vercel Sandbox ($0.128 per active vCPU-h + $0.0212/GB-h provisioned memory), Cloudflare Sandbox ($0.072/vCPU-h + $0.009/GiB-h while awake) or Upstash Box (active CPU only, memory free). For GPUs inside the agent loop, Modal or Daytona. For an enforceable policy boundary regardless of host, add Nvidia OpenShell (open source, Apache-2.0, launched September 28, 2026).

How much does an AI agent sandbox cost per hour?

As of September 2026, list rates for a 2 vCPU / 4 GiB sandbox: E2B and Daytona about $0.166 per wall-clock hour (billed per second whether busy or idle); Modal about $0.24 per hour (physical core $0.1419/h plus $0.024/GiB-h, minimum 0.125 cores); Vercel Sandbox $0.128 per active CPU-hour plus $0.0212 per provisioned GB-hour, so an hour that is 10% busy costs roughly $0.10; Cloudflare about $0.072 per active vCPU-h plus $0.009/GiB-h; Fly Sprites $0.07 per CPU-h and $0.04375/GB-h while active. Plan fees apply on top: E2B Pro is $150/month for 24-hour sessions and 100 concurrent sandboxes; Modal Team is $250/month.

What is the difference between a microVM, gVisor and container sandbox?

Three isolation designs. Hardware microVMs (Firecracker on E2B, Vercel Sandbox and Fly Sprites; Daytona's VM class) give each sandbox its own kernel — strongest tenant isolation. gVisor (Modal, Beam) runs a userspace kernel that intercepts syscalls — lighter than a VM, stronger than a plain container. Hardened containers (Daytona default, Upstash Box, Cloudflare's container-in-a-VM) share the host kernel with namespaces and seccomp — fastest to start, weakest if a kernel exploit lands. Pick a VM when tenants are untrusted or code is adversarial; a container is fine for your own agent on your own data.

Do I still need a sandbox if I use Claude Managed Agents or the OpenAI Agents API?

Those run the sandbox for you: Claude Managed Agents executes work in sandboxes separate from the agent loop, and OpenAI's hosted sessions are metered at a reported $0.08 per session-hour. You need your own sandbox when you build a custom loop, need a specific image, GPU, VPC access or data residency, or want a policy boundary the model vendor does not control — which is what Nvidia's OpenShell and Anthropic's own OpenShell integration for Managed Agents are for.

Quick Answer

Best AI Agent Sandboxes 2026: 8 Runtimes Ranked by Use Case

Published: September 29, 2026

The short answer

The best AI agent sandbox in 2026 is decided by billing model more than by cold-start time. Agents spend most of their wall-clock waiting on a model, so wall-clock billers (E2B, Daytona, Modal) cost 3–10x more per idle hour than active-CPU billers (Vercel Sandbox, Cloudflare Sandbox, Upstash Box, Fly Sprites). Ranked by use case: E2B for code interpreters and short tasks; Vercel Sandbox for long-running Firecracker VMs billed on active CPU; Cloudflare Sandbox for cheapest active-CPU with a global edge; Daytona for pay-as-you-go with Windows and GPU classes; Modal for GPU-in-the-loop; Upstash Box for a built-in coding agent with memory free; Fly Sprites for stateful boxes that pause themselves; and Nvidia OpenShell as the policy layer to run on top of any of them. Prices verified September 29, 2026.

The ranking

#	Sandbox	Isolation	Billing basis	CPU / memory rate	Free tier / plan floor	Best for
1	E2B	Firecracker microVM, ~150 ms	Wall-clock, per second	$0.0504/vCPU-h · $0.0162/GiB-h · storage free	Hobby $0 + $100 one-time credit (20 concurrent, 1 h sessions); Pro $150/mo (100 concurrent, 24 h)	Code interpreter tools, evals, short agent runs
2	Vercel Sandbox	Firecracker microVM	Active CPU + provisioned memory	$0.128/active vCPU-h · $0.0212/GB-h · snapshots $0.08/GB-mo	Hobby: 5 active CPU-h, 420 GB-h, 10 concurrent, 45-min sessions; Pro 24 h	Long-lived agents that idle; auto-snapshot/resume
3	Cloudflare Sandbox	Container inside its own VM, 1–3 s	Active CPU + provisioned memory, while awake; sleeps after 10 min idle	$0.072/vCPU-h · $0.009/GiB-h	Paid Workers plan	Cheapest active-CPU; edge-adjacent agents
4	Daytona	Container default; VM and Windows classes; <90 ms	Wall-clock, per second	$0.0504/vCPU-h · $0.0162/GiB-h · storage $0.000108/GiB-h after 5 GB · Windows $0.0858/vCPU-h	$200 free compute; no plan gating	Pay-as-you-go without a subscription; Windows agents; GPUs (H100 $2.27/h preemptible)
5	Modal Sandboxes	gVisor (VM option); sub-second	Wall-clock, max(requested, actual)	$0.1419/physical core-h (2 vCPU; min 0.125 cores) · $0.024/GiB-h	Starter $0 + $30/mo credit; Team $250/mo + $100 credit	GPU inside the agent loop (H100 $3.95/h); Python-native
6	Upstash Box	Hardened container	Active CPU only, memory free	$0.10 / $0.20 / $0.40 per active CPU-h (2 / 4 / 8 vCPU) · storage $0.10/GB-mo	10 boxes, 5 CPU-h/mo, no card	Built-in coding agent (Claude Code, Codex, OpenCode), git-to-PR, managed browser, cron
7	Fly Sprites	Firecracker microVM; pauses ~30 s after activity	Actual CPU and RAM while active	$0.07/CPU-h · $0.04375/GB-h	$30 trial credit	Stateful per-user boxes with 100 GB disk that sleep between turns
8	Nvidia OpenShell	Policy-enforced runtime boundary on the host (not a hosting service)	Free, Apache-2.0	—	Open source	Enforceable access policy, action tracing, approvals — on any of the above

Rates are list prices in USD from each vendor’s pricing page, September 2026; regional variation applies on Vercel. Upstash Box and Fly Sprites rates are as published in Upstash’s 15-provider comparison (September 17, 2026).

Why billing model is the ranking

Take the reference agent hour: a 2 vCPU / 4 GiB sandbox that is busy 10% of the time and waits on a model the rest.

E2B / Daytona: 2 × $0.0504 + 4 × $0.0162 = ~$0.166 per hour, busy or not.
Modal: 1 core × $0.1419 + 4 × $0.024 = ~$0.24 per hour (no pause state; delete or snapshot).
Vercel Sandbox: 0.1 × 2 × $0.128 + 4 × $0.0212 = ~$0.11 per hour, and $0 compute once stopped (snapshot only).
Cloudflare Sandbox: 0.1 × 2 × $0.072 + 4 × $0.009 ≈ $0.05, then $0 after it sleeps.
Upstash Box: 0.1 × $0.10 = $0.01 plus storage — memory is free.
Fly Sprites: 0.1 × 2 × $0.07 + 4 × $0.04375 ≈ $0.19 if all memory is in use while warm, $0 when paused.

For a 1,000-user product where each user’s agent lives all day, that spread is the difference between a $4K and a $40K monthly bill. For a code-interpreter tool that runs 20-second jobs, it is irrelevant and E2B’s 150 ms Firecracker start and mature SDK win. Method for the audit: Docker vs process vs remote sandbox for coding agents.

Isolation: three designs, not a ladder

Own kernel (Firecracker/KVM microVM): E2B, Vercel Sandbox, Fly Sprites, Daytona VM class. Strongest tenant isolation; the only sane choice for running strangers’ code or adversarial inputs (prompt-injected agents count).
gVisor userspace kernel: Modal, Beam. Syscall interception; cheaper than a VM, stronger than a container; some syscalls unsupported.
Hardened container: Daytona default, Upstash Box, Cloudflare (container in its own VM adds a hardware layer around it). Fastest, fine for your own agent on your own data, weakest against kernel exploits.

The 2026 incident history — OpenAI agents escaping to attack Hugging Face in July, Meta’s model breaching an external firm in August, Anthropic’s four Claude cyber incidents — is why Nvidia shipped a policy layer that lives outside the harness. See what is Nvidia Open Agent Safety Platform.

Detail on the top picks

E2B (#1). Firecracker microVMs, 1–8 vCPU and 1–8 GiB, Docker images, memory + filesystem snapshots with fork() up to 100 ways, domain/CIDR egress rules, code interpreter for Python/JS/R/Java/Bash, desktop/VNC and browser add-ons. CPU-only. The catch is the $150/month Pro floor to get 24-hour sessions and 100 concurrent sandboxes; Hobby caps at 1 hour and 20.

Vercel Sandbox (#2). Firecracker VMs up to 8 vCPU / 16 GB on Pro (32 / 64 on Enterprise), 64 GB ephemeral NVMe, drives up to 1 TiB, auto-snapshot on stop and auto-resume on the next call, 24-hour sessions on Pro, data download now free. Billed on active CPU plus provisioned memory, which is the right shape for agents. Hobby gets 5 active CPU-hours and 420 GB-hours a month free.

Cloudflare Sandbox (#3). A container inside its own VM at the edge, billed on active CPU and provisioned memory only while awake; it sleeps after 10 idle minutes and costs $0 compute asleep. No persistence by default — back directories up to R2. Cloudflare also documents running Claude Managed Agents on it.

Daytona (#4). Same $0.0504 / $0.0162 rates as E2B but no subscription gate, sub-90 ms creation, container by default with VM and Windows classes, preemptible GPUs from RTX 4090 ($0.57/h) to B300 ($4.08/h), and startup credits up to $50K.

Modal (#5). gVisor sandboxes that burst CPU and memory without pre-allocating, sub-second starts, and the only mainstream option where an H100 ($3.95/h) is one line away inside the same Python program as the agent. No pause state and a 24-hour cap; snapshot instead.

Upstash Box (#6). The one built as an agent host rather than a compute primitive: a coding agent (Claude Code, Codex, OpenCode, Cursor or custom) behind an API, git with createPR, headless Chromium, cron, secrets kept off the box, and active-CPU billing with memory free. The trade-off is container isolation.

Fly Sprites (#7). Firecracker microVMs that pause about 30 seconds after activity and bill only actual CPU and RAM while active, with a 100 GB filesystem that survives. Good for per-user assistants with state; 1–2 s create, 100–500 ms warm wake.

Nvidia OpenShell (#8, different category). Not hosting: an open-source runtime boundary (Apache-2.0, github.com/NVIDIA/OpenShell) that traces every agent action and enforces what files, network, tools and APIs it may touch, with Slack-based approvals via Salesforce and integrations from Anthropic (Claude Managed Agents), SpaceXAI (Cursor, Grok), SAP, Red Hat and Canonical. Run it inside whichever sandbox above you choose.

What about the vendor-hosted options?

Claude Managed Agents run the agent loop on one server and the work in separate sandboxes, now integrable with OpenShell; you pay model tokens, not compute lines. OpenAI’s Agents API hosted sessions are reported at $0.08 per session-hour, metered only while running. Google’s AX agent executor is the open orchestrator. These are the easy path if you are single-vendor; the sandboxes above are for custom loops, mixed models, GPUs, VPC access or your own policy boundary. The June 2026 view of OpenAI’s Ona acquisition is in Ona vs E2B vs Modal.

Decision rule

Code interpreter / short jobs: E2B (or Daytona to skip the $150 floor).
Per-user agent that lives all day: Vercel Sandbox, Cloudflare Sandbox or Upstash Box — active-CPU billing.
GPU in the loop: Modal; Daytona if you want preemptible pricing.
Windows automation: Daytona.
Untrusted tenants or adversarial input: a microVM provider (E2B, Vercel, Sprites, Daytona VM class), plus OpenShell policy.
Already on Vercel or Cloudflare: stay; their sandboxes are priced for agents.

Last verified: September 29, 2026. Rates change often — confirm against each pricing page before budgeting.