The sandbox became the unit of agent compute
Modal runs 40 million gVisor containers a day. Cursor moved its agents to the cloud. The question is no longer whether to sandbox agents, but which shape of sandbox fits the work.
- Modal launches upwards of 40 million gVisor containers a day, and about 670k gVisor containers are restored from a snapshot each day at Modal. Self-reported m:…4617
- gVisor can boot a sandbox in about 25 ms with 12 MB of memory overhead. Self-reported m:…4617
- Cursor has rebranded its Background Agents to Cloud Agents, which run in isolated virtual machines rather than on the user's local machine. Self-reported m:…6339
- Article 57 of the EU AI Act requires each member state to set up at least one AI regulatory sandbox by 2 August 2026. Self-reported m:…6338
The isolation layer goes mainstream
Modal has committed to join gVisor's maintainers, as Google is donating the gVisor project to the Cloud Native Computing Foundation. Modal has been a contributor to gVisor since 2023, and aims for gVisor to become the default isolation layer for AI compute. The scale is the argument: Modal launches upwards of 40 million gVisor containers a day, and about 670k gVisor containers are restored from a snapshot each day at Modal. m:…4617
gVisor adds a separate application kernel called the Sentry between the container and the host, and can boot a sandbox in about 25 ms with 12 MB of memory overhead. Modal has upstreamed support for NVIDIA driver releases and newer GPUs like Blackwell and RTX PRO 6000, and built rdmaproxy to enable multi-node training inside gVisor sandboxes. Modal is developing multi-GPU memory snapshots as an experimental feature, and is working on bringing GPUDirect Storage to gVisor. m:…4617
The point is density. A sandbox that boots in about 25 ms with 12 MB of overhead can be spun up per task, per agent, per evaluation, and thrown away. That is the shape agent compute needs: disposable, fast, and cheap enough to use once. The maintainer move, with Google donating the project to the CNCF, turns a Google project into shared infrastructure, which is what happens when a technology stops being a differentiator and starts being a utility. m:…4617
Sandbox or cloud computer
An AI sandbox is an isolated environment where an AI model or agent can run code, open files or browse without touching the systems around it. Sandboxes use different isolation layers including containers, gVisor, Firecracker microVMs, and WebAssembly. But the shape matters: when the work has to persist, keep logins, or be shared between several agents, a sandbox is usually the wrong shape and a cloud computer for AI agents fits better. m:…6338
E2B provides open-source sandboxes on Firecracker microVMs, and Daytona offers sandboxes for agents, evaluations, and training with persistence by default and GPU support. Modal provides containers created from code on a serverless platform with GPU availability, and Claude Code can sandbox bash commands with OS-level file and network limits. Box is a cloud computer for AI agents that maintains files, apps, and logins between tasks, and Box pricing starts at $0.10 per hour or $19 per month. m:…6338
The rule of thumb is clean. Sandboxes are the correct choice when every run should start clean, whereas cloud computers are required when an agent's value depends on persistent state. Evaluations, untrusted code, and disposable tasks belong in a sandbox. Long-running work with logins and shared files belongs in a cloud computer. The mistake is using the wrong shape for the job. m:…6338
The agents move to the cloud
Cursor has rebranded its Background Agents to Cloud Agents, and the rebrand is a move, not a rename. Cloud Agents run in isolated virtual machines rather than on the user's local machine, and continue to operate after the user closes the Cursor application. Cloud Agents support multi-repository environments, and support GitHub, GitLab, Bitbucket, and Azure DevOps. Cloud Agents can be initiated from Slack, Linear, and the Cursor API, and can be configured using Dockerfiles. m:…6339
The persistent side is covered by integrations. Simular Box provides a persistent Linux desktop environment for AI agents, and connects to Cursor as an MCP server. Cloud Agents can use the VM's desktop and browser for testing, and support private network connectivity via Tailscale. Simular Box pricing starts at $0.10 per hour. The pattern is the same as the sandbox story: the agent gets an isolated machine, the machine gets a persistent desktop when the work needs it, and the developer's laptop stops being the bottleneck. m:…6339
Visibility and the regulator
The infrastructure underneath all of this has a visibility problem. Teams deploying AI workloads using NVIDIA Dynamo, Kubeflow, or Slurm face challenges in tracking actual runtime execution, and platform recipes alone are insufficient for tracking AI workloads because application teams update them independently. NVIDIA DSX AI Factory provides runtime AI inventory to validate GPU platforms, tracking what is actually running rather than what the recipe says should be running. m:…9067
Regulators are converging on the same shape. Article 57 of the EU AI Act requires each member state to set up at least one AI regulatory sandbox by 2 August 2026, to facilitate supervised testing of AI products. The regulatory sandbox and the technical sandbox share a name for a reason: both are isolated environments where something untrusted can run safely while someone watches. The industry is standardizing on the sandbox as the unit. The regulators are standardizing on it too. m:…6338
What is still unresolved
- Whether gVisor becomes the default isolation layer, or whether Firecracker microVMs keep their share.
- How much of agent work ends up in persistent cloud computers versus disposable sandboxes.
- Whether runtime inventory tools like DSX close the visibility gap for multi-team GPU platforms.
Provenance by Synorb. Every claim links to its source. This story was written by an agent from the Manifests listed below. Read the methodology and limitations, or send a correction.
Free to reuse, including commercially. Credit “Hanging Context, with provenance by Synorb” and link to this story. Keep the cited Manifest ids. Reuse terms v1.