Best Sandboxes for Coding Agents: 2026 Comparison

Your PR review agent clones the monorepo, installs dependencies, runs the test suite, and posts a review. Twenty minutes later a second commit lands on the same branch, and the agent clones the whole repository again. The sandbox from the first call was gone the moment the review finished. Every review now pays the clone and install cost before analysis starts. The bill tracks the size of the repo, not the size of the diff.

This guide compares sandboxes for coding agents across five platforms: Blaxel, E2B, Vercel Sandbox, Daytona, and Cloudflare Sandbox SDK. It's written for engineering leaders choosing the execution layer for a coding, PR review, or app-builder agent heading to production.

Key takeaways

• Coding agents need fast resume, full state restore, and hardware-level isolation across dozens of calls per session.
• Blaxel resumes from standby in under 25ms with filesystem, memory, and running processes intact.
• E2B keeps paused sandboxes indefinitely and resumes them in about one second.
• Vercel Sandbox snapshots the filesystem on stop and starts a new session from that snapshot.
• Daytona's container class and Cloudflare's containers lacklacks the dedicated guest kernel microVMs provide, while Cloudflare's containers have their own dedicated kernel. Cloudflare sleeps after 10 idle minutes by default.

What makes a sandbox work for coding agents?

A code execution sandbox for AI agents is an isolated compute environment. The agent runs code it generated at runtime, with no access to the host, other tenants, or the wider network. A coding agent sandbox adds what a developer workstation has. That means a cloned repo, installed dependencies, a running dev server, and a preview URL.

Four criteria separate a sandbox that holds up in production from one that works in a demo:

• Resume speed: The gap between an agent's call and a ready environment. Agents make dozens of sequential calls, so a two-second delay per call becomes a stalled session.
• State fidelity: What comes back after a pause. Some platforms restore memory and running processes; others restore only the filesystem and restart everything else.
• Isolation: Containers are the industry standard for running your own trusted software in multi-tenant settings. Untrusted AI-generated code needs microVM isolation, because a container shares the host kernel with neighboring workloads.
• Networking and compliance: Custom domains for preview URLs, egress control, and secrets kept out of the sandbox. Your buyers also request SOC 2 or Health Insurance Portability and Accountability Act (HIPAA) evidence.

For coding agents, the repo and its dependencies should survive between sessions so the agent never re-clones. Preview URLs should stay stable while the environment sleeps. And an agent exploring two fixes at once needs parallel sandboxes, ideally forked from the same prepared state.

Get these wrong and users read per-call latency as a broken product. Security reviews also stall when a customer asks how tenants are separated.

Coding agent sandboxes compared at a glance

The table compares isolation, resume, retention and compliance, using each vendor's own documentation.

Blaxel and E2B charge no compute while a sandbox is idle, and Blaxel bills snapshot storage during standby. Daytona bills reserved resources while a sandbox is started. Its auto-stop window after each session is paid idle time. Vercel bills Active CPU only while code runs but charges memory for the whole session in one-minute increments.

1. Blaxel

Blaxel is the infrastructure foundation for autonomous agents. Its Sandboxes are the execution layer for agents that write and run code. A sandbox stays in standby at zero compute cost. It resumes in under 25ms with filesystem, memory, and running processes intact. Each sandbox runs in its own microVM on a custom Firecracker fork on bare metal. That's the same microVM technology AWS Lambda runs on. Model-written code never shares a kernel with another tenant, which removes the shared-kernel escape path containers expose. When connections close, the sandbox returns to standby automatically. A PR review agent pays for compute only while a review runs.

Strengths:

• Standby with full state: Filesystem, memory, and running processes survive standby, so the agent skips clone and install on every return. For guaranteed long-term retention, pair standby with Volumes.
• Snapshots and forking (private preview): Fork a prepared sandbox so an agent can try two fixes in parallel from the same installed state.
• First-class sandbox provider in the OpenAI Agents SDK: The Blaxel tutorial wires a coding agent to a sandbox. It sets image, region, memory, pause-on-exit, and time-to-live (TTL) options.
• Claude Managed Agents and Claude Code: Anthropic's Managed Agents run against an Anthropic-managed or self-hosted sandbox. Blaxel's docs include a Managed Agents tutorial plus a guide connecting Claude Code to a Blaxel sandbox.
• Networking: Custom domains on preview URLs and per-workload outbound domain filtering. Proxy secrets injection means API keys never enter the sandbox (public preview). Dedicated egress gateways provide static IPs (private preview).
• Agent Drive (private preview): Co-located shared storage mounted by several sandboxes at once. A planner agent and its workers read the same repo and artifacts without copying.
• Compliance: SOC 2 Type II, ISO 27001, and a HIPAA BAA available as an add-on.

Tradeoffs:

• CPU-only: No GPU sandboxes, so training or large-model inference belongs on a GPU platform. Daytona offers a GPU class in this group.
• No air-gapped deployment: On-premise options are limited to private endpoint connectivity and bring-your-own-metal, with the control plane staying on Blaxel's side.

Pick Blaxel when the agent returns to the same environment repeatedly and users must not notice the resume.

2. E2B

E2B is an open-source sandbox platform whose managed sandboxes run as microVMs on Google Cloud. Bring Your Own Cloud (BYOC) deployment on AWS and GCP puts the infrastructure in your own account. Paused sandboxes are kept indefinitely, with no TTL and no automatic deletion, and they aren't billed while paused. Pause saves filesystem and memory. Resume takes about one second.

Strengths:

• Open source with BYOC: The Apache-2.0 core plus BYOC on AWS and GCP gives you an exit path if the managed service stops fitting.
• Multi-language runtime: The Code Interpreter SDK executes Python, JavaScript, TypeScript, R, Java, and Bash in a Jupyter-based environment. Official client SDKs cover JavaScript and Python.
• Pause without a clock: A paused sandbox stays paused indefinitely at no charge, comparable to Blaxel's standby retention, minus the resume speed.

Tradeoffs:

• Resume speed: One second per resume is visible across a session with repeated pauses. That's where E2B and Blaxel diverge most for interactive agents.
• Timeout kills by default: Sandboxes run 1 hour on Hobby and 24 hours on Pro. Pausing and resuming resets the window. But the default onTimeout is "kill", so an unattended agent loses its environment unless you opt into pause.
• No managed secrets proxy in GA: E2B's enterprise page describes secrets resolved at egress through a private-beta proxy.

E2B fits teams that want open-source code and indefinite pause and can accept a one-second resume.

3. Vercel Sandbox

Vercel Sandbox runs each sandbox in a microVM with a dedicated kernel. Persistence is on by default. When a sandbox stops, Vercel snapshots the filesystem, and a later start resumes from it. Hobby sessions cap at 45 minutes and Pro or Enterprise at 24 hours. The clock resets on each stop and resume.

Strengths:

• Persistent by default: No lifecycle flags to set. The filesystem comes back on the next start, which covers the re-clone problem for an app-builder agent.
• SDKs and agent support: JS/TS and Python SDKs. Vercel's 18 May 2026 changelog added Claude Managed Agents support.
• Concurrency headroom: 10 concurrent sandboxes on Hobby and 10,000 on Pro and Enterprise.

Tradeoffs:

• Resume is a new session: Vercel documents the snapshot on stop as filesystem-only. The agent has to restart a dev server, a database connection, or a half-finished test run after every stop.
• No published resume figure: Vercel's docs say "start in milliseconds" without a number, so measure it yourself before committing a latency budget.

Choose Vercel Sandbox when your stack already runs on Vercel and filesystem continuity is enough.

4. Daytona

Daytona offers sandboxes in three classes: containers by default, plus VM and GPU classes. Container sandboxes auto-stop after 15 minutes of inactivity and preserve the filesystem. VM sandboxes auto-pause at 60 minutes and keep memory too. GPU sandboxes are deleted on auto-stop. Stopped containers auto-archive after 7 days by default and 30 days at most.

Strengths:

• IDE integration: Native connections to VS Code, Cursor, Windsurf, and JetBrains integrated development environments (IDEs) over SSH. A web terminal and Virtual Network Computing (VNC) are also available.
• Computer Use API: Programmatic desktop interaction for agents that need to drive a graphical user interface (GUI) as well as a shell.
• Broad SDK coverage: Daytona SDKs cover Python, TypeScript, Ruby, Go, and Java, plus a REST API and Model Context Protocol (MCP) server.
• Compliance and previews: SOC 2 Type II and a HIPAA BAA, plus a custom preview proxy for preview URLs under your own domain.

Tradeoffs:

• Paid idle after every session: Reserved resources bill per second until auto-stop, after the agent has finished.
• Container isolation by default: The container class doesn't give each sandbox its own guest kernel the way microVMs do. Containers are the industry norm for trusted code and a weaker boundary for AI-generated code. The VM class exists but isn't the default.
• Resume time undocumented: Daytona publishes no official resume or creation figure.

Daytona suits teams that want IDE-connected environments and can accept the idle window and default container boundary.

5. Cloudflare Sandbox SDK

Cloudflare's Sandbox SDK is generally available and runs each sandbox as a dedicated Linux container tied to a Durable Object. It lives inside the Workers platform: you deploy with wrangler, coordinate through Durable Objects, and store artifacts in R2. By default a sandbox sleeps after ten idle minutes and loses its state. Cloudflare also documents R2 backup and restore.

Strengths:

• Workers-native: Durable Objects give each sandbox a stable identity, and R2 holds files. Everything deploys through the workflow a Workers team already runs.
• R2 backup and restore: The SDK writes R2 backups of directories and restores them into a fresh sandbox. Cloudflare documents these as directory backups, so restores cover files only.
• Configurable sleep: sleepAfter adjusts the idle timeout and keepAlive: true holds a container up. Since Cloudflare stops charging only after an instance sleeps, a kept-alive container keeps billing.

Tradeoffs:

• Ephemeral on sleep: Files and processes are gone once the sandbox sleeps. A coding agent re-clones on every return unless you script backups to R2. Blaxel's comparison with Cloudflare Sandbox walks through what that costs an agent.
• Container isolation: Container-based isolation shares the host kernel across workloads, the boundary microVM platforms avoid for untrusted code.
• TypeScript only: The SDK ships as @cloudflare/sandbox for TypeScript, so Python agent stacks need a Worker in front. Custom instances top out at 4 vCPU and 12 GiB.

Use Cloudflare when Workers is already your platform and each agent call can start from a clean container.

Which sandbox fits which coding agent workload?

Match the platform to how often your agent comes back to the same environment and what it expects to find there.

• Blaxel: Coding agents, PR review agents, and app builders that return to one environment all day. They need memory and processes back before the user notices. Not for GPU work or air-gapped sites.
• E2B: Teams that want open-source code, BYOC, and indefinite pause, and whose agents tolerate a visible resume between calls.
• Vercel Sandbox: Vercel-hosted products where filesystem continuity is enough and the agent can restart its own processes after each stop.
• Daytona: IDE-centric workflows, Computer Use, or a GPU class in the same account, where a paid idle window per session is acceptable.
• Cloudflare Sandbox SDK: Workers-native teams running short, stateless executions at the edge, with R2 backups covering the files that matter.

Choose a code execution sandbox built for production agents

Match the sandbox to how your agent resumes. An agent whose sandbox restores memory and processes picks up mid-task. One that restores only files re-runs setup, and one that restores nothing re-clones. AI agent workloads in production that write and run code hit that resume path on every tool call. Per-call delays compound across calls until the session feels broken.

For coding agents that revisit the same environment, agent infrastructure platforms like Blaxel keep Sandboxes in standby at zero compute cost and restore the full environment on resume. Volumes add guaranteed long-term storage, and Agent Drive (private preview) provides co-located shared storage for repos and artifacts across agents. E2B is an alternative for teams prioritizing open source and BYOC, Vercel fits products that need filesystem continuity, Daytona emphasizes IDE-connected environments and GPU options, and Cloudflare suits short Workers-native executions.

Frequently asked questions

What is the best sandbox for coding agents?

PR review and app-builder agents return to the same repo repeatedly. The best sandbox for them restores memory and running processes on resume. It also isolates each tenant in a microVM and charges no compute while idle. Blaxel meets all three for CPU workloads. E2B is the pick for open-source and BYOC requirements, and Daytona for IDE-connected or GPU work.

How do microVMs differ from containers for AI-generated code?

Containers share the host kernel and are the industry standard for running your own trusted software in multi-tenant settings. MicroVMs give each workload its own guest kernel behind hardware virtualization. You need that boundary when a model wrote the code at runtime. A kernel exploit inside one container can reach the host and neighboring tenants. An exploit inside a microVM stops atis generally contained by the hypervisor boundary, but vulnerabilities in the hypervisor, VMM, or virtualized devices can allow an escape.

How fast should a coding agent sandbox resume?

A coding agent sandbox should resume quickly enough that repeated tool calls do not make the session feel stalled. Blaxel reports a standby resume in under 25 milliseconds, while E2B documents a resume time of about one second.

Can a sandbox keep state for weeks without compute cost?

Yes, on two of the platforms here. Blaxel keeps a sandbox in standby indefinitely, with no compute charge and only snapshot storage billed. It restores memory and processes on resume. Use Volumes for guaranteed persistence, since standby isn't a durability guarantee. E2B keeps paused sandboxes indefinitely at no charge and restores memory in about a second.