Antigen
Continuous offensive security for the enterprise.
Infrastructure Engineer
About the role
Zag is building the platform for AI review agents. As coding agents produce more changes than humans can review, every team will need custom review agents, tailored to their codebase and their standards, running on every proposed change. We're building the infrastructure that makes that possible.
Review agents need real environments to do useful work. They need to build code, run tests, boot applications, and interact with them. Zag provisions these environments as ephemeral sessions on dedicated Apple Silicon that boot in seconds from pre-warmed snapshots. Every session exposes a durable, replayable stream. Getting this right, fast, reliable, and seamless for the teams that depend on it, is the core infrastructure challenge at Zag.
As a founding infrastructure engineer, you'll own the systems that make this work. That includes macOS virtualization and session lifecycle, compute provisioning and scheduling, the streaming and observability layer, and the integration points between Zag's orchestration engine and the sandboxed environments where agents run.
You should be comfortable working across the stack. On a given week you might be optimizing VM boot times, building out the session streaming protocol, debugging an Xcode build failure inside an agent environment, or designing how we scale from managed Apple Silicon to our own bare-metal fleet.
This is a foundational role. The infrastructure you build will define what Zag's agents can do and how fast they can do it. You'll work directly with the founders, ship to production daily, and have real ownership over the platform from day one.
What we're looking for:
- Strong systems engineering background. You've built and operated infrastructure that other engineers depend on.
- Experience with virtualization, containers, or sandboxed compute environments. macOS virtualization experience (Tart, Anka, or similar) is a plus but not required.
- Comfort with low-level systems work: networking, file systems, process management, performance optimization.
- Proficiency in at least two of: TypeScript, Go, Swift, Rust.
- Familiarity with Apple's build toolchain (Xcode, xcrun, simulators, codesigning) is a strong plus.
- You care about reliability and you care about speed. The engineers and agents using Zag's infrastructure need both.
About Antigen
Zag
About Zag
Coding agents are changing how software gets written. Tools like Claude Code and Codex can author changes faster than any team can review them, and the gap is only getting wider. The bottleneck in software development is shifting from writing code to validating it.
We think every serious engineering team will need review agents: custom agents, tailored to their codebase, their standards, and the specific behaviors they care about, running on every proposed change to their main branch. Static AI code review with inline comments won't scale. The kind of confidence that lets teams merge as fast as they author comes from agents that actually build, test, and run the code.
As human engineering work moves up a layer of abstraction, we believe a tech lead's primary job will be tuning better review agents. Not reading diffs line by line, but shaping the automated judgment that enforces their team's engineering culture at the scale of AI-authored code.
Zag is the platform for building and running those review agents. You describe agents in TypeScript or Swift as composable Tasks. Zag runs them in real sandboxed environments with real build tools, real test suites, and real running applications on every PR.
Today, we've opened early access to teams building for Apple platforms. Zag provisions dedicated Apple Silicon with Xcode, simulators, and the full native toolchain, so review agents can do what humans do: build the project, boot the app, and verify that it works.
How We Got Here
Zag is inspired by the system Google uses to validate code across its internal monorepo, where every proposed change is reviewed by both humans and automated agents before it can land. We believe that model, built for a world where machines participate in the review loop as first-class citizens, is the right shape for what's coming.
The Team
Zag is built by a small team from Google and Tesla based in San Francisco. We're backed by Y Combinator and building in the open at zag.dev.
Working at Zag
We're early. The product is live, the infrastructure works, and the first teams are onboarding. What we're building now will define the platform for a long time. You'll work directly with the founders, ship to production daily, and have real ownership over the systems you build.
We care about craft, clear thinking, and building something that engineers actually trust. If the idea of shaping how AI-authored code gets validated, and doing it by building beautiful, reliable infrastructure, sounds like your kind of problem, we'd love to talk.
