compare · reviewed 2026-10-27
Firecracker vs semantic
Firecracker is an Apache-2.0 virtual machine monitor for KVM microVMs, with a jailer that applies cgroup and namespace isolation and drops privileges. [1] It runs on Linux. [1]
Firecracker is a building block: networking is TAP devices with rate limiters, and there is no egress policy engine, credential broker or agent log. [1] Semantic provides those on top of microVM isolation.
| Firecrackeropen source VMM | Semantic (smx)microVM + policy on your machines | |
|---|---|---|
| Isolation | KVM microVM plus jailer [1] | One microVM per agent, own kernel |
| Where it runs | Self-hosted VMM [1] | Managed private beta; on-prem for enterprise (contact us) |
| Egress rules | not documented (TAP networking and rate limiters) [1] | Security profiles enforced by host firewall; metadata and link-local always closed |
| Credentials kept out | not documented | Git tokens, SSH keys and model sign-ins stay on the host |
| File, Git, SSH permissions | not documented | Per path, repo, branch and SSH host; deny beats allow; enforced on the host |
| Tamper-evident agent log | not documented (logs and metrics) | Hash-chained log of runs, events and refusals; read with smx agent logs |
| Snapshots, pause/resume | Snapshots GA with pause/resume API [2] | Snapshot, pause and resume with memory, disk and running processes |
| Local hosts (Linux / WSL2 / macOS) | Linux only [1] | Linux (KVM) and Windows via WSL2; macOS planned |
| License | Apache-2.0 [1] | Proprietary (private beta) |
Firecracker, per its docsSemanticnot documented in the vendor's public docs
Which one fits
When Firecracker fits better
- You are building your own sandbox platform and want a minimal, hardened VMM. [1]
- You need direct control over the VM API and snapshots. [2]
When Semantic fits better
- You want sandboxes for agents now, not a platform to build.
- Agents work on your repos and you need branch-level Git and per-path file permissions enforced outside the agent.
- You need a tamper-evident log of what the agent did inside the sandbox, including refusals.
Restoring snapshots safely
Firecracker's docs warn that restoring the same snapshot more than once is insecure, because clones share random and crypto state. [2] Semantic reseeds sandboxes restored from the same snapshot so they never share random state.
Questions
Does Firecracker run on macOS?
No, it needs Linux with KVM. [1]
Does Firecracker filter egress?
Not by itself; it provides TAP networking and rate limiters. [1]
Sources
- Firecracker repository · last verified 2026-10-27
- Firecracker snapshot support · last verified 2026-10-27