Best Agent Sandboxes in 2026: Cold Start, Per-Second Pricing, and Network Policy Across E2B, Daytona, Modal, Cloudflare, and Vercel

A new open-source benchmark from ComputeSDK measuring Time to Interactive across five agent sandbox platforms found Daytona fastest at a 0.27s median but with only a 37% success rate, while Vercel Sandbox posted a 0.67s median with 100% success in the August 21, 2026 run. The comparison covers E2B, Daytona, Modal, Cloudflare, and Vercel, highlighting that cold start, filesystem persistence, egress policy, and idle billing are the key architectural differentiators.

Every agent that writes code needs somewhere to run it. That “somewhere” is now a product category with at least a dozen vendors, four incompatible billing models, and marketing pages that quote cold starts measured under conditions nobody publishes. This comparison fixes the units. It covers the five platforms most teams shortlist — E2B https://e2b.dev/ , Daytona https://www.daytona.io/ , Modal Sandboxes https://modal.com/docs/guide/sandboxes , Cloudflare Sandbox SDK https://developers.cloudflare.com/sandbox/ , and Vercel Sandbox https://vercel.com/docs/sandbox — along with Runloop https://docs.runloop.ai/docs/devboxes/overview , Fly.io Sprites https://sprites.dev/ , and Northflank https://northflank.com/product/sandboxes where they change the answer. The four questions that actually decide this Feature matrices for this category are mostly noise. Four properties change architecture, and everything else is a preference: Cold start under concurrency : An agent loop that creates a sandbox per tool call pays this tax thousands of times a day. Filesystem persistence between turns : Does turn 2 see the pip install from turn 1, or does the agent rebuild its world? Egress policy : Can the sandbox reach the internet, can you turn that off, and can you change your mind mid-session? Idle billing : Agents spend most of their wall-clock waiting on a model. Somebody is paying for those seconds. 1. Cold start: what the numbers actually say The vendor claims are not comparable to each other. Daytona’s pricing page advertises sub-90ms sandbox creation https://www.daytona.io/pricing . E2B is commonly cited at roughly 150ms. Modal advertises sub-second cold starts for pre-cached containers https://modal.com/resources/code-sandbox . None of these state concurrency, region, image size, or whether the clock stops at API acknowledgment or at first executed command. The most useful public dataset is ComputeSDK’s sandbox leaderboard https://www.computesdk.com/benchmarks/sandboxes/ , which is open source and runs on a schedule. It measures Time to Interactive TTI : elapsed time from create to the first successful command inside the sandbox, 100 iterations per provider, launched concurrently in a single burst, from a 4 vCPU host in Northern Virginia. Results from the August 21, 2026 run: | Provider | Median TTI | P95 | P99 | Success rate | |---|---|---|---|---| | Vercel Sandbox | 0.67s | 1.04s | 1.12s | 100% | | Modal | 0.88s | 1.00s | 1.08s | 100% | | Runloop | 0.89s | 3.27s | 3.50s | 100% | | E2B | 1.61s | 1.77s | 1.81s | 100% | | Cloudflare | 5.06s | 6.04s | 6.48s | 100% | | Daytona | 0.27s | 0.43s | 0.44s | 37% | Three things in that table matter more than the ranking. Burst is not the same test as sequential : Daytona’s fastest published median is real, and on an earlier provider-page run https://www.computesdk.com/benchmarks/daytona/ it created sandboxes at a 0.10s median when launched one at a time. On the August burst run it posted the fastest median in the field and completed 37 of 100 attempts. A median you only reach on a third of your calls is not a latency number, it is a capacity number. Retry logic is not optional on any of these platforms. Tail latency is the number to design against : Runloop’s median and Modal’s median are 10ms apart. Runloop’s P95 is 3.3x Modal’s. If your agent’s UX budget is one second, the median tells you almost nothing. Cloudflare is measuring a different product : Sandbox SDK sits on Cloudflare Containers https://developers.cloudflare.com/containers/ , which schedules a container instance and boots an image. That is architecturally a heavier operation than resuming a pre-warmed Firecracker VM, and 5s medians reflect it. Cloudflare’s own GA post https://blog.cloudflare.com/sandbox-ga/ is candid about the shape of the problem: booting a sandbox, cloning a repo, and running npm install takes about 30 seconds, while restoring the same environment from a backup takes about two. Reproducing this yourself The task worth measuring is the one your agent runs, not echo hello . A useful harness runs the same unit of work everywhere: install pandas, read a CSV, plot it, return a PNG. Time four checkpoints separately. php checkpoints: t create - t ready - t deps - t result run 100 iterations sequential, then 100 concurrent, report median/P95/P99 import time, statistics def one run provider : t0 = time.perf counter sbx = provider.create API acknowledged t1 = time.perf counter sbx.exec "python -c 'print 1 '" first command returns: TTI t2 = time.perf counter sbx.exec "pip install pandas matplotlib" t3 = time.perf counter sbx.exec "python /work/plot.py" writes /work/out.png png = sbx.read file "/work/out.png" t4 = time.perf counter sbx.kill return dict create=t1-t0, tti=t2-t0, deps=t3-t2, task=t4-t3, bytes=len png Report tti and task separately. Vendors optimize the first and readers care about the second. Pin the region, pin the image, and publish both the sequential and the concurrent series, because they answer different questions. 2. Per-second pricing, normalized Published rates as of August 27, 2026, converted to a common unit. Modal prices per physical core, which it defines as 2 vCPU, so the vCPU-equivalent is shown for comparison. | Platform | CPU | Memory | Billing basis | Plan floor | |---|---|---|---|---| | Daytona https://www.daytona.io/pricing Modal Sandbox https://modal.com/pricing max request, actual , per second Vercel Sandbox https://vercel.com/docs/sandbox/pricing active CPU only Cloudflare Sandbox https://developers.cloudflare.com/containers/pricing/ active CPU only Fly.io Sprites https://sprites.dev/ Runloop https://runloop.ai/pricing Northflank https://northflank.com/pricing Two footnotes that people get wrong. - Modal’s sandbox tier is roughly 3x its standard Function rate $0.00003942 vs $0.0000131 per core-second , and region selection adds 1.5–1.75x https://modal.com/pricing on top. Sandbox pricing is not Modal’s headline compute pricing. - Daytona’s GPU rates are widely reproduced at $3.95/hr for an H100. Its live pricing page https://www.daytona.io/pricing lists on-demand H100 at $2.27/hr and H200 at $2.61/hr. Third-party comparison tables in this category go stale within a quarter. 3. Cost per 1,000 executions Rates are not costs. The model below fixes the workload and runs it through each rate card. Assumptions: 2 vCPU / 4 GiB sandbox, 1,000 executions, no plan floor included, no egress, default region Vercel iad1 , Cloudflare standard-3 at 2 vCPU / 8 GiB / 16 GB disk since instance sizes are fixed . Scenario A: short burst — 90s alive, 50% average CPU | Platform | Cost / 1,000 | Composition | |---|---|---| | Northflank | $1.67 | $0.83 CPU + $0.83 memory | | Cloudflare | $3.70 | $1.80 CPU + $1.80 memory + $0.10 disk | | E2B / Daytona | $4.14 | $2.52 CPU + $1.62 memory | | Vercel | $5.32 | $3.20 active CPU + $2.12 memory | | Modal | $5.95 | $3.55 CPU + $2.40 memory | | Fly Sprites | $7.88 | $3.50 CPU + $4.38 memory | | Runloop | $7.92 | $5.40 CPU + $2.52 memory | Scenario B: idle-heavy — 10 min alive, 5% average CPU This is what a real agent loop looks like. The sandbox is open, the model is thinking, nothing is running. | Platform | Cost / 1,000 | Change vs A | |---|---|---| | Northflank | $11.11 | 6.7x | | Cloudflare | $13.87 | 3.7x | | Vercel | $16.27 | 3.1x | | E2B / Daytona | $27.60 | 6.7x | | Modal | $39.66 | 6.7x | | Fly Sprites kept awake | $52.50 | 6.7x | | Runloop kept running | $52.80 | 6.7x | Vercel moves from 4th-cheapest to 3rd, and its CPU line drops from $3.20 to $2.13 while everyone else’s scales linearly. Cloudflare’s active-CPU line falls to $1.20. That is the entire argument for active-CPU billing, and it is worth roughly 2x on this workload. Scenario B with suspend The platforms that lose Scenario B can win it back, if your orchestration suspends between turns instead of holding the box open. Same workload, 30s awake per execution: | Platform | Cost / 1,000 | Mechanism | |---|---|---| | E2B auto-pause | ~$2.16 | Pause costs ~4s per GiB of RAM, resume ~1s | $2.62 $2.64 E2B’s number includes ~17s of pause and resume overhead for a 4 GiB sandbox. That overhead is the deciding variable: pausing is only economical when the gap between turns is meaningfully longer than the pause itself. Fly’s idle detector is specific about what counts as activity: an in-flight HTTP or API request, output to a session’s stdout, an open TCP connection, or an active task sprites.dev https://sprites.dev/ . An agent that holds a connection open while it waits is an agent that is billed. Redirecting output to a file does not count, which is a real lever. 4. Filesystem persistence between turns This is where the platforms diverge most, and where the wrong choice shows up as a rebuilt node modules on every turn. | Platform | Default on stop/idle | Memory state | Mechanism | |---|---|---|---| E2B | onTimeout defaults to kill | Pause preserves RAM and running processes | pause / connect | Daytona Stop, archive, pause, fork, volumes https://www.daytona.io/docs/en/persistence Modal timeout default 5 min, max 24h Filesystem snapshots https://modal.com/docs/guide/sandbox-snapshots are Images, 30-day default TTL Cloudflare disk resets to image , R2 mounts, snapshots rolling out https://developers.cloudflare.com/sandbox/api createBackup / restoreBackup Vercel Snapshots https://vercel.com/docs/sandbox/pricing , 30-day default expiry, $0.08/GB-mo Runloop Pro plan only Fly Sprites Three details worth internalizing: E2B’s default kills your work : onTimeout is kill unless you set lifecycle: { onTimeout: 'pause' } at creation. The killed state is terminal, and the docs describe no shutdown signal before termination. Treat unsaved work as lost. Cloudflare’s disk is ephemeral across sleep : Container docs https://developers.cloudflare.com/containers/platform-details/architecture/ state plainly that a sleeping instance restarts with a fresh disk from its image. Backup and restore to R2 works today; the automatic persistAcrossSessions disk snapshot announced at GA was still rolling out at the time of writing. Daytona splits persistence by sandbox class : Container sandboxes preserve the filesystem across stop/start but do not support pause, so memory is cleared every time. Linux VM sandboxes support both. GPU sandboxes are ephemeral and are deleted on stop; results have to be written to a volume. 5. Egress policy Every platform in this comparison can now run a sandbox with no internet access. The differences are in precedence, granularity, and whether policy can change without a restart. | Platform | Default | Block all | Allowlist | Change at runtime | |---|---|---|---|---| E2B | Open egress | allowInternetAccess: false | Domains, IPs, CIDRs; wildcards | Yes, updateNetwork replaces the whole policy | Daytona | Tier-dependent | networkBlockAll | domainAllowList 20 max , networkAllowList 10 CIDRs, IPv4 only | Yes, Tier 3/4 only | Modal | Open egress, no inbound | block network=True | outbound cidr allowlist , outbound domain allowlist beta | Alpha, and only if allowlists were set at create | Cloudflare | Open egress | enableInternet = false | allowedHosts / deniedHosts , glob patterns | Yes, handlers and host rules apply live | Vercel | allow-all | deny-all , including DNS | Domains via SNI, plus IP/CIDR fallback | Yes, without restarting | Runloop | Network policies per devbox | Yes | Yes | Documented per devbox | The precedence trap E2B and Vercel resolve conflicts in opposite directions. In E2B, allow rules take precedence over deny rules https://docs.e2b.dev/network/internet-access : an IP in both lists is allowed. In Vercel Sandbox, denied ranges override allowed ranges. A policy ported from one to the other without rewriting it does not mean the same thing. The failure-mode trap E2B documents that blocked TCP connections can look successful from inside the sandbox. The firewall accepts the connection before deciding whether the destination is allowed, so a socket opens and no packets arrive. Verify egress with an application-level response — an HTTP status, a TLS handshake — not with a successful connect . Any test suite that asserts “network is blocked” by checking for a connection error will pass against an unblocked sandbox. Credential injection is the real differentiator Blocking egress is table stakes. Letting a sandbox make an authenticated call without ever holding the credential is not. Cloudflare runs outbound handlers in the Workers runtime, outside the sandbox , with access to Workers bindings. The sandbox issues a plain request, the handler attaches the secret, and ctx.containerId scopes credentials per instance docs https://developers.cloudflare.com/sandbox/guides/outbound-traffic/ . Vercel brokers credentials on egress with matchers scoped by path, method, query string, or headers, and states the firewall runs on the host outside the microVM where sandbox code cannot disable it Vercel https://vercel.com/blog/a-sandbox-without-a-network-boundary-is-only-half-a-sandbox . E2B ships per-host request transforms in public beta that inject headers at the egress proxy, including workload-identity tokens the sandbox never sees. Runloop offers a Credential Gateway with opaque token injection. For agents processing untrusted input, this design matters more than cold start. A prompt-injected agent with a GitHub token in its environment is a different incident from one that can only reach GitHub through a proxy holding the token. 6. Isolation, limits, and the fine print | Platform | Isolation | Max session | Concurrency | GPU in sandbox | Self-host / BYOC | |---|---|---|---|---|---| | E2B | Firecracker microVM | 1h Hobby, 24h Pro; resets after pause | 20 Hobby, 100 Pro, up to 1,100 | No | | gVisor https://modal.com/docs/guide/sandbox-networking keepAlive available 24h Pro https://vercel.com/docs/sandbox/pricing 7. How to choose Pick Vercel Sandbox if your agent waits on models more than it computes, and you want the cheapest measured burst cold start in this set. Active-CPU billing is worth roughly 2x on idle-heavy loops, the egress firewall with credential brokering is now available on every plan, and the 0.67s median with a 1.12s P99 was the tightest distribution in the August run. Pick E2B if you need per-session kernel isolation for adversarial code, want memory-state persistence across turns, or need a self-host path. Set onTimeout: 'pause' on day one. Budget for the $150/mo Pro floor as soon as you exceed 20 concurrent sandboxes or 1-hour sessions. Pick Daytona if persistence is the product and you can absorb capacity variance. The stop/archive/pause/fork lifecycle is the most developed in the category, forking a live VM with memory intact has no clean equivalent elsewhere, and the compute rate matches E2B without a subscription floor. Pick Modal if any part of the agent’s work touches a GPU. It is the only platform here with a full GPU rate card inside the sandbox, T4 through B300. Price the 3x sandbox multiplier and regional multipliers before you commit. Pick Cloudflare Sandbox if your app already lives on Workers and your egress security model matters more than your cold start. Programmable egress handlers running outside the sandbox with binding access are genuinely differentiated. Five-second burst medians are not, so hold sandboxes open per session rather than creating one per tool call, and plan for disk that resets on sleep. Pick Runloop if you are building a coding agent and need SWE-Bench-style evaluation in the same platform. Note that suspend/resume, the feature that fixes its idle economics, is gated behind the $250/mo Pro plan. Pick Fly Sprites if you want a persistent computer per user rather than a disposable one per call, and Northflank if you need the lowest published rate, GPU support, and self-serve BYOC in one platform. Key Takeaways - Measured burst cold start spreads 7x across providers: Vercel 0.67s, Modal 0.88s, E2B 1.61s, Cloudflare 5.06s. - Vendor "sub-90ms" and "~150ms" claims describe sequential creates, not the concurrent bursts agents actually generate. - Billing model beats headline rate: the cheapest provider flips depending on how long your sandbox sits idle. - Only Vercel and Cloudflare bill CPU on active use; E2B, Daytona, Modal and Runloop bill wall-clock while the box is alive. - Every platform here can now deny egress by default, but allow/deny precedence and TCP failure behavior differ in ways that break assumptions. Sources: E2B pricing https://e2b.dev/pricing , E2B persistence https://docs.e2b.dev/sandbox/persistence , E2B internet access https://docs.e2b.dev/network/internet-access , Daytona pricing https://www.daytona.io/pricing , Daytona persistence https://www.daytona.io/docs/en/persistence , Daytona network limits https://www.daytona.io/docs/en/network-limits , Daytona billing https://www.daytona.io/docs/en/billing , Modal pricing https://modal.com/pricing , Modal sandbox networking https://modal.com/docs/guide/sandbox-networking , Modal sandbox resources https://modal.com/docs/guide/sandbox-resources , Modal sandbox snapshots https://modal.com/docs/guide/sandbox-snapshots , Cloudflare Containers pricing https://developers.cloudflare.com/containers/pricing/ , Cloudflare outbound traffic https://developers.cloudflare.com/sandbox/guides/outbound-traffic/ , Cloudflare Sandboxes GA https://blog.cloudflare.com/sandbox-ga/ , Vercel Sandbox pricing https://vercel.com/docs/sandbox/pricing , Vercel Sandbox firewall https://vercel.com/docs/sandbox/concepts/firewall , Runloop pricing https://runloop.ai/pricing , Sprites https://sprites.dev/ and Northflank pricing https://northflank.com/pricing Michal Sutter is a data science professional with a Master of Science in Data Science from the University of Padova. With a solid foundation in statistical analysis, machine learning, and data engineering, Michal excels at transforming complex datasets into actionable insights.