In 2026, agents write code faster than any team can review it, and every line they write needs an isolated machine to run in. Isolating untrusted code is an old problem, and Google built gVisor to solve it inside its own cloud; agents have made it every engineering team's problem.
That puts the sandbox vendor in the critical path of every coding and computer-use agent. Solari is the faster and cheaper choice when your agent needs to run code, browse the web and operate a desktop from one account; Modal fits teams whose sandboxes sit next to the GPU training and inference they already run on Modal. This guide compares the two on speed, price and fit.
Why Does the Sandbox Choice Matter Now?
A year ago most agents called a model and returned text. Today they clone repositories, install packages, run tests and open browsers, and each of those steps runs on a real machine. Running that code on your own servers puts your data and credentials one bad command away from the agent.
A sandbox moves that risk into a disposable machine. The vendor you pick decides three things for your agent: how fast each task starts, what each hour costs at volume, and how strong the wall is between one agent's code and the next.
Solari vs Modal at a Glance
Which Is Faster, Solari or Modal?
Solari is faster on a sandbox's full lifecycle. Creating the machine, running the same workload and tearing it down takes 8.2 s on Solari against 11.9 s on Modal.
Start time is close on both. A Solari machine starts usually in about a second, and Modal says its Sandboxes deliver sub-second cold starts even on custom and large images and scale to a million sandboxes in under a minute.
For an agent that opens a fresh machine per task, start and teardown repeat on every task. Across a batch of thousands of tasks, the faster lifecycle returns results sooner and keeps fewer machines waiting.
Which Is Cheaper, Solari or Modal?
Solari is cheaper per sandbox hour at list price. A 4 vCPU, 8 GB sandbox with 20 GB of disk costs $0.114 per hour on Solari and $0.761 per hour on Modal's Sandboxes tier.
Modal bills Sandboxes at three times its standard list rate because they run non-preemptible, and it charges the higher of what you request and what you use. That suits bursty code, and it means a large reservation keeps billing while the code sits idle.
Solari bills per second while an environment runs, and you can pause a sandbox for free between tasks. Snapshots bill at $0.05 per GB-month after the first 10 GB, so keeping a prepared machine on hand costs little.
What Can You Run on Each?
Both run agent-generated code in isolation; they differ in what surrounds the code. These are the jobs teams put on sandboxes first:
Coding agents. The agent clones a repository, installs dependencies and runs the tests inside a disposable machine. On Solari, named shells and Git operations keep the working directory and variables between calls, so a long fix never restarts from scratch.
Reinforcement learning rollouts. Reinforcement learning runs many graded episodes in parallel, each from the same starting state. Solari forks fresh sandboxes from one prepared snapshot; Modal pairs rollouts with GPU sandboxes and its own training API, which suits teams that train on Modal.
Data analysis. The agent loads a dataset, runs Python and charts the result. Solari keeps Python state between calls and returns charts as images, so the agent builds on its last step instead of reloading the data.
Web tasks next to code. An agent that collects pages and then processes them needs a browser and a sandbox. Solari browsers are ready in 8 ms, run Playwright as is, and bill to the same account as the sandbox.
Computer use. Models with computer use operate apps through a screen, clicking and typing like a person. A Solari desktop is a full Linux computer with a live view your agent sees and operates, and a person can watch or take over.
What Role Does Solari Play?
Solari gives an agent every machine it needs from one API. Solari launched with browsers, sandboxes and desktops on one account and one bill, so your agent runs code and operates the web without a second vendor.
Hardware isolation by default. Each Solari sandbox is a microVM of its own with a dedicated kernel, separated by hardware virtualization. Modal runs sandboxes on gVisor, a userspace kernel that filters system calls, or on a VM runtime with its own Linux kernel for workloads that need one.
State that survives a pause. Pause saves memory and processes, and resume brings the sandbox back exactly as it was. Your agent can stop mid-task, wait for a review and pick up at the same line.
Fleet scale. With Solari you can launch up to 100,000 sandboxes at once, so a whole queue of pull requests or rollouts runs in one pass. Size each one from 1 to 8 CPUs to match the job.
Save points and forks. Snapshot a running machine, revert it after a failed attempt, or start copies from it. Setup runs once, and every later task opens ready to work.
Which Should You Choose?
Choose Solari when your agents run code, browse and operate desktops, when cost per sandbox hour decides the budget at volume, and when you want a microVM boundary around every task. Stay with Modal when your sandboxes belong next to GPU training and inference you already run there. Modal is the more established vendor with the larger ecosystem across GPUs, inference and training; Solari is the younger company and moves faster on speed and price.
What Comes Next for Agent Sandboxes?
Over the next year, the sandbox becomes the default workspace for agents in four ways:
One machine per task. Agents will open a fresh sandbox for every task and throw it away after, so lifecycle speed matters more than idle capacity.
The whole computer. Coding agents will test their own work in a browser and on a desktop, not only in a terminal.
Long-running work. Agents will pause for hours while a person reviews, then resume with memory intact.
Isolation in every security review. Buyers will ask what separates one agent's code from the next before they sign.
What stays human is judgment: which code ships, which access an agent gets, and who reviews the diff before it merges. The best teams will spend their engineers on those calls and hand the rest to agents.
Get Started With Solari
Start with one job, such as running your coding agent's tests in a fresh sandbox for every pull request, then fork from a snapshot once it runs cleanly. Solari is the fastest and cheapest way to run cloud browsers and VMs for coding and computer-use agents. Get started with a free account and start running your agents today.
