Firecracker vs gVisor vs Kata Containers: which isolation for AI agents?

01What is each one, in a sentence?

They answer the same question, how to run code you do not trust on a Linux host, at different layers. Firecracker is a building block you program against. gVisor and Kata are runtimes that slot into Docker, containerd or Kubernetes in place of the default runc, so the workload still arrives as an OCI container image.

All three are Apache-2.0 licensed. Firecracker came from Amazon Web Services and runs Lambda and Fargate. gVisor is written in Go. Kata Containers is stewarded by the Open Infrastructure Foundation.

• Firecracker: a VMM that runs in user space and uses KVM to create microVMs, with 5 emulated devices and a separate jailer process as a second line of defence.
• gVisor: in its own words, an application kernel that implements a Linux-like interface and runs in user space; its Sentry intercepts system calls and a Gofer process handles file access. It ships as the OCI runtime runsc.
• Kata Containers: lightweight virtual machines that feel and perform like containers, compatible with the OCI image format and the Kubernetes CRI, run by the containerd-shim-kata-v2 runtime with a kata-agent inside each VM.

02Firecracker vs gVisor vs Kata at a glance

The table below compares them on the four things that usually decide the choice. It is built from each project's own documentation, read on 31 October 2026. Start-up figures are each project's own claims, not a benchmark we ran.

Kata's row depends on which hypervisor you configure. Its docs list Cloud Hypervisor, Firecracker, QEMU, Dragonball and StratoVirt, and mark only QEMU as supporting GPUs and confidential-computing technologies such as Intel TDX and AMD SEV-SNP.

• Boundary. Firecracker: hardware virtualization; the guest has its own kernel. gVisor: the Sentry, a user-space kernel, in front of the host kernel. Kata: hardware virtualization; one VM per pod with its own guest kernel.
• Syscall path. Firecracker: system calls go to the guest's Linux kernel, and only device I/O crosses to the host. gVisor: every system call is handled by the Sentry, which uses a smaller set of host calls. Kata: as Firecracker, through whichever hypervisor it runs.
• Platform. Firecracker: x86_64 and aarch64 Linux with read/write access to /dev/kvm. gVisor: x86_64 and ARM64 Linux 5.6 or later; the Systrap platform works without virtualization support. Kata: Linux hosts with hardware virtualization; its architecture document assumes physical hardware.
• Start-up. Firecracker: under 125 ms per its project page. gVisor: no kernel to boot, so a sandbox starts like a process. Kata: a VM boot, with the time set by the hypervisor and guest kernel you pick.

03Is gVisor a VM?

Not in the usual sense, and its docs say so: gVisor describes itself as not a VM in the everyday sense of the term, and as a third approach that keeps many of a VM's security benefits with a lighter footprint. It can be read as a merged guest kernel and VMM, or as seccomp on steroids. There is no guest operating system and no virtual hardware; the Sentry reimplements the Linux system call interface in a host process.

That design has two documented costs. gVisor does not implement every system call, /proc file or /sys file, so some software fails in ways it would not on Linux. And it warns of higher per-system-call overhead and possibly poor performance for system-call-heavy workloads. Fly.io's comparison makes the same point for agent loops: installs, git and test runs make many small file and network calls, which is where the extra layer shows.

gVisor can still use KVM. Its platform docs describe a KVM platform that runs best on bare metal and the Systrap platform, the default since mid-2023, which is the better choice inside a VM or on a machine without virtualization support. That flexibility is why it appears in Kubernetes environments where nested virtualization is not available.

04Firecracker vs Kata: a VMM or a runtime?

The comparison people search for is a little lopsided, because Kata can use Firecracker. Firecracker on its own gives you an API socket to configure a machine, attach a kernel, a root filesystem and network devices, and start it. Everything above that, images, networking, lifecycle, snapshots and multi-tenant scheduling, is yours to build, which is what services such as AWS Lambda, Fly.io and E2B did.

Kata starts from the container world instead. You keep your OCI images and your Kubernetes manifests, select Kata as the runtime class, and each pod gets a VM. Choosing Kata does not mean choosing Firecracker: the hypervisor is a configuration setting, and the trade-offs in the table follow from it.

05Which isolation for untrusted code from AI agents?

No single answer fits every team, and the three are often combined with other controls rather than chosen alone. A few questions narrow it. Does the agent run syscall-heavy work such as package installs, compilers and test suites, or short CPU-bound snippets? Do your hosts expose KVM, or are they cloud VMs without nested virtualization? Do you already run Kubernetes and want isolation through a runtime class, or are you building your own service?

Whichever you pick, the isolation primitive does not decide what the sandbox can reach or which credentials it holds. Network egress rules, where API keys live and how you undo a bad change come from the system around the VM or the Sentry, and those matter as much as the kernel boundary when an agent has been prompt-injected.

• Building a sandbox service on KVM hosts: Firecracker gives the smallest VMM to build on.
• Kubernetes, hosts without usable KVM, short CPU-bound jobs: gVisor, through runsc and a runtime class.
• Kubernetes with VM-level isolation per pod: Kata, with the hypervisor chosen for the features you need.

06None of the three runs natively on a Mac. What do Mac users do?

Firecracker needs /dev/kvm, gVisor needs Linux 5.6 or later, and Kata runs on Linux hosts. macOS has no KVM; it offers Apple's Hypervisor and Virtualization frameworks instead. So on a Mac, all three run only inside a Linux VM, and Firecracker or Kata inside that VM also needs nested virtualization, which Apple supports from macOS 15 on Macs with the M3 chip or later.

Mac users therefore pick one of three routes: a Linux VM through a tool such as Lima, with nested virtualization switched on when the chip allows it; a tool that builds its sandboxes directly on Apple's Virtualization framework, such as Apple's own Containerization package, or Docker Desktop, whose Linux VM runs on Apple's Virtualization framework or Docker's own VMM; or a remote Linux host with KVM. Our companion post on Firecracker and Apple silicon walks through each.