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Nullspace currently has a default Firecracker guest kernel lane and an opt-in FUSE-capable lane for shared volumes and bucket mounts. The Python SDK does not yet expose Template.with_kernel(...), so kernel choice is an environment lane, not a per-template SDK method.

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Current lanes

LaneUse it forCurrent selector
DefaultGeneral sandboxes and templatesRuntime host NULLSPACE_KERNEL_PATH default
FUSE-enabledShared volumes, s3fs, gcsfuse, JuiceFSSet NULLSPACE_KERNEL_PATH to vmlinux.fuse and use the matching rootfs
For private beta, use a deployment lane whose host kernel and rootfs are both FUSE-capable when you need shared volumes or bucket mounts. Until an explicit SDK selector ships, do not document or call Template.with_kernel(...).

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Kernel version

The default local download lane uses Firecracker 1.14.1 and attempts the Firecracker Linux 5.10 guest kernel artifact for the host architecture. The FUSE builder pins NULLSPACE_FUSE_LINUX_VERSION=5.10.252 unless overridden. Check the actual running guest when exact version matters: 
from nullspace import Sandbox

with Sandbox.create(template="base") as sandbox:
    print(sandbox.commands.run("uname -r", shell=True).stdout.strip())
On a runtime host, operators can inspect the configured artifact path: 
echo "${NULLSPACE_KERNEL_PATH:-./.local/artifacts/vmlinux}"
test -f "${NULLSPACE_KERNEL_PATH:-./.local/artifacts/vmlinux}.config" \
  && grep '^CONFIG_FUSE_FS=' "${NULLSPACE_KERNEL_PATH}.config"

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Template compatibility

Snapshot-backed templates record kernel compatibility metadata. If a runtime host cannot restore a template or snapshot safely because the kernel or architecture differs, the request fails explicitly instead of silently creating an incompatible sandbox. Concepts: Create, Resume. API reference: buildTemplate, createSandbox.