Modal Labs / modal.com Modal Labs Raises $355M at $4.65B Valuation as AI Agent Sandboxes Become Critical Infrastructure
Modal closed a $355M Series C led by General Catalyst and Redpoint on May 21, crossing $300M ARR after 5x growth in eight months. Its sandbox product — which powers code execution for Devin, Windsurf, and several Claude Managed Agent partners — now accounts for more than a third of revenue.
Modal Labs announced a $355 million Series C on May 21, raising its post-money valuation to $4.65 billion. General Catalyst and Redpoint led the round, with Redpoint taking a board seat. Accel, Menlo Ventures, and Bain Capital Ventures also participated, along with all existing investors doubling down.
The company hit over $300 million in annualized revenue, up 5x from around $60 million at its Series B close in September 2025. That’s eight months of growth.
What Modal Actually Does
Modal is a serverless GPU platform. You write Python, decorate a function with @app.function, and Modal runs it on the appropriate GPU, scales it to zero when idle, and handles the rest. The initial pitch was infrastructure for ML engineers who don’t want to manage cloud instances. That market is real, but a different product line is now driving more than a third of revenue: sandboxes.
A Modal Sandbox is an isolated container environment for running untrusted code. The platform has launched over one billion of them. AI coding agents need this. When Devin runs a user’s code, that code can’t execute on shared production infrastructure. When a Claude Managed Agent builds a web app, it needs somewhere to run and test it. When an RL training run generates thousands of code samples to evaluate, each evaluation needs its own environment.
Scott Wu, CEO of Cognition (which makes Devin and Windsurf), put it plainly: “Modal powers both our reinforcement learning infrastructure and production inference. Millions of sandboxes on one end, real-time serving on the other.”
DoorDash CTO Andy Fang also cited Modal by name when Anthropic announced Claude Managed Agents self-hosted sandboxes at Code with Claude London on May 19, two days before this funding announcement: “As we scale agentic commerce for local businesses, we need a highly efficient path to production with full harness control, scale, and reliability.” DoorDash is one of four launch partners running Claude Managed Agents on Modal infrastructure.
Why This Round Is Large
The $355M in a single round for a 120-person company across New York, San Francisco, and Stockholm is notable. Modal’s CEO Erik Bernhardsson has said the next phase involves low-latency inference scaling and collapsing training-inference loops for reinforcement learning workflows — both GPU-intensive. The round also expands the sandboxing infrastructure that’s increasingly load-bearing for the agentic software engineering stack.
A billion sandboxes isn’t a marketing number. It reflects how many discrete code-execution events AI agents have generated in roughly 18 months of this product category existing. Each one is a separate Modal API call. At the current trajectory of agent deployments, that number compounds quickly.
The Infrastructure Layer
Modal sits a level below the AI coding tools that get most of the attention. Cursor, Windsurf, and Claude Code are the interfaces. The underlying execution environments that make them safe to run at scale are less visible. This round is a signal that the infrastructure layer has gotten large and is accelerating.
The round closed in two tranches: a first close at $2.5 billion valuation and the larger second tranche at $4.65 billion.
Sources: Modal Series C announcement — Modal Labs, May 21, 2026; Serverless AI infrastructure startup Modal Labs seals $355M funding round — SiliconAngle; Claude Managed Agents: Self-hosted sandboxes and MCP Tunnels — Anthropic