2026 guide to agent sandboxes: cold start times, pricing models, and network policies across major platforms

In 2026, the landscape of agent sandboxes has evolved significantly, with multiple platforms offering distinct features and pricing models. A comprehensive comparison of the top platforms—E2B, Daytona, Modal Sandboxes, Cloudflare Sandbox SDK, and Vercel Sandbox—along with Runloop, Fly.io Sprites, and Northflank, highlights key differences in performance and cost efficiency. The comparison focuses on cold start times, per-second pricing, and network policies, which are critical for developers running code in isolated environments. The most useful public dataset for evaluating these platforms is ComputeSDK’s sandbox leaderboard, which measures Time to Interactive (TTI) as the time from the creation of a sandbox to the first successful command executed within it. The dataset runs 100 iterations per provider, launched concurrently from a 4 vCPU host in Northern Virginia. Results from an August 21, 2026, run show that the task being measured is more important than the benchmark of echoing 'hello'. A useful harness installs pandas, reads a CSV, plots it, and returns a PNG, with separate timing for each checkpoint. Pricing models vary significantly, with Modal pricing per physical core, defined as 2 vCPU, and the vCPU-equivalent shown for comparison. Published rates as of August 27, 2026, are converted to a common unit, with assumptions of 2 vCPU / 4 GiB sandbox, 1,000 executions, and default regions. Vercel moves from the fourth-cheapest to third, with its CPU line dropping from $3.20 to $2.13, while Cloudflare’s active-CPU line falls to $1.20. This represents a significant cost advantage for active-CPU billing. The platforms differ in how they handle idle detection and billing. E2B’s idle detector includes ~17s of pause and resume overhead for a 4 GiB sandbox, making pausing economical only when the gap between executions is longer than the pause itself. Fly’s idle detector considers in-flight HTTP or API requests, output to stdout, open TCP connections, or active tasks as activity, meaning an agent holding a connection open is billed. Redirecting output to a file does not count as activity, which is a key lever for cost optimization. Network policy and credential management are also critical. Every platform in the comparison now supports sandboxes with no internet access, but differences exist in precedence, granularity, and the ability to change policies without a restart. E2B and Vercel resolve conflicts in opposite directions: E2B allows rules take precedence over deny rules, while Vercel denies ranges override allowed ranges. E2B documents that blocked TCP connections can appear successful from inside the sandbox, as the firewall accepts the connection before checking the destination. Cloudflare runs outbound handlers in the Workers runtime, outside the sandbox, with access to Workers bindings. The sandbox issues a plain request, and the handler attaches the secret, with credentials scoped per instance. Vercel brokers credentials on egress with matchers scoped by path, method, query string, or headers, and the firewall runs on the host outside the microVM, where sandbox code cannot disable it. E2B ships per-host request transforms in public beta, injecting 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, these design choices are more important than cold start times. A prompt-injected agent with a GitHub token in its environment represents a different incident than one that can only reach GitHub through a proxy holding the token. Sources include E2B pricing, Daytona pricing, Modal pricing, Cloudflare Containers pricing, and Vercel Sandbox pricing, among others.