Modal's Sandbox API provides isolated containers with process I/O, custom images, configurable CPU and memory, secrets, volumes, networking controls, and snapshots. Its V2 backend is explicitly aimed at workloads needing more than 20 sandbox creates per second or more than 10,000 concurrent sandboxes.12 AgentVM is solving a different scaling problem: how to give an agent a bounded, inspectable Linux server and a safe way to acquire it.34
If your primary metric is sandbox throughput, Modal and AgentVM are not really chasing the same target. If your primary requirement is a temporary machine that behaves like infrastructure and can be bought by an agent, the comparison becomes much more interesting.
Modal is an execution platform first
Modal Sandboxes expose a process-style interface with exec, stdin, stdout, stderr, custom images, volumes, secrets, resource sizing, and networking options. Modal also provides Functions and other serverless primitives around the same platform.12
That model is well suited to applications that need large fleets of short-lived execution environments, structured concurrency, warm pools, or cloud resources that are controlled directly from application code.
AgentVM is a machine lifecycle product first
AgentVM provisions Linux machines that are expected to be reached over SSH and managed as servers. It exposes plans, regions, images, machine state, expiry, and connection details rather than presenting the VM only as a child process of an SDK call.3
This is intentionally less abstract. An agent can install packages, run daemons, expose an endpoint, reconnect later, or hand the same machine to a human operator using familiar server tooling.
Security boundaries are expressed differently
Modal documents secure-by-default sandbox networking, including blocked inbound access by default and configurable outbound restrictions.2 Those controls are attractive when arbitrary code needs a tightly specified execution network.
AgentVM's standard machine model emphasizes SSH public-key access, managed firewall behavior, bounded runtime, and keeping cloud-provider credentials out of the agent's possession.3 The security model is therefore closer to managed server tenancy than to a sandbox policy object.
Machine payments are the AgentVM-specific layer
AgentVM's MPP endpoints let an autonomous client encounter a payment challenge for bounded compute and satisfy it as part of the HTTP workflow.4 This is useful when the agent itself is expected to acquire temporary infrastructure within a budget.
Modal's public sandbox documentation focuses on account-authenticated SDK and platform operations.1 Teams that already have a Modal account and application control plane may prefer that model; teams experimenting with machine-paid resources may care more about AgentVM's purchasing boundary.
Choose for concurrency or for computer ownership
Choose Modal when you need serverless functions, very high sandbox concurrency, image-based execution, sophisticated sandbox networking, or an application-native process API. Those are core strengths of the platform's current sandbox design.
Choose AgentVM when a job should own a temporary server-shaped resource with SSH, provider-backed placement, an explicit lifetime, and a payment/lifecycle envelope that an agent can understand.