diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index bbed8ba..9f8a794 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -23,18 +23,29 @@ env:
 
 jobs:
   # ==========================================================================
-  # Build kernel for each architecture (native runners, no cross-compile).
+  # Build kernel for each architecture x flavor (native runners, no
+  # cross-compile). `system` boots the VZ/HV System VM; `microvm` boots
+  # Firecracker sandbox microVMs (arm64-only for now — Firecracker x86_64
+  # needs an ELF vmlinux and its own config).
   # ==========================================================================
   build-kernel:
-    name: Build Kernel (${{ matrix.arch }})
+    name: Build Kernel (${{ matrix.arch }}, ${{ matrix.flavor }})
     runs-on: ${{ matrix.runner }}
     strategy:
       matrix:
         include:
           - arch: arm64
+            flavor: system
+            artifact: kernel-arm64
             runner: ubuntu-24.04-arm
           - arch: x86_64
+            flavor: system
+            artifact: kernel-x86_64
             runner: ubuntu-24.04
+          - arch: arm64
+            flavor: microvm
+            artifact: microvm-kernel-arm64
+            runner: ubuntu-24.04-arm
 
     steps:
       - name: Checkout
@@ -56,6 +67,7 @@ jobs:
         run: |
           USE_DOCKER=0 \
           ARCH=${{ matrix.arch }} \
+          FLAVOR=${{ matrix.flavor }} \
           KERNEL_VERSION=${{ env.KERNEL_VERSION }} \
           OUTPUT_DIR="$(pwd)/output" \
           ./scripts/build-kernel.sh
@@ -63,15 +75,15 @@ jobs:
       - name: Generate checksum
         run: |
           cd output
-          sha256sum "kernel-${{ matrix.arch }}" > "kernel-${{ matrix.arch }}.sha256"
+          sha256sum "${{ matrix.artifact }}" > "${{ matrix.artifact }}.sha256"
 
       - name: Upload kernel artifact
         uses: actions/upload-artifact@v4
         with:
-          name: kernel-${{ matrix.arch }}
+          name: ${{ matrix.artifact }}
           path: |
-            output/kernel-${{ matrix.arch }}
-            output/kernel-${{ matrix.arch }}.sha256
+            output/${{ matrix.artifact }}
+            output/${{ matrix.artifact }}.sha256
           retention-days: 14
 
   # ==========================================================================
@@ -92,11 +104,11 @@ jobs:
       - name: Prepare release files
         run: |
           mkdir -p release
-          for ARCH in arm64 x86_64; do
-            DIR="artifacts/kernel-$ARCH"
-            if [ -f "$DIR/kernel-$ARCH" ]; then
-              cp "$DIR/kernel-$ARCH" "release/kernel-$ARCH"
-              cp "$DIR/kernel-$ARCH.sha256" "release/kernel-$ARCH.sha256"
+          for NAME in kernel-arm64 kernel-x86_64 microvm-kernel-arm64; do
+            DIR="artifacts/$NAME"
+            if [ -f "$DIR/$NAME" ]; then
+              cp "$DIR/$NAME" "release/$NAME"
+              cp "$DIR/$NAME.sha256" "release/$NAME.sha256"
             fi
           done
           echo "=== Release files ==="
@@ -112,8 +124,9 @@ jobs:
             Self-compiled Linux kernel for ArcBox VMs (`CONFIG_MODULES=n`, all drivers built-in).
 
             ### Files
-            - `kernel-arm64` — ARM64 Image (Apple Silicon / ARM VMs)
-            - `kernel-x86_64` — x86_64 bzImage
+            - `kernel-arm64` — ARM64 Image, System VM (Apple Silicon / ARM VMs)
+            - `kernel-x86_64` — x86_64 bzImage, System VM
+            - `microvm-kernel-arm64` — ARM64 Image, Firecracker sandbox microVMs
           files: release/*
           draft: false
           prerelease: ${{ contains(github.ref_name, 'alpha') || contains(github.ref_name, 'beta') }}
diff --git a/CLAUDE.md b/CLAUDE.md
index 16eddb9..7749879 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -6,6 +6,23 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 
 `arcbox-kernel` provides optimized Linux kernel and initramfs builds for ArcBox VMs, targeting Apple Virtualization.framework (primary) and KVM (secondary).
 
+Two kernel **flavors** build from the same source — do not conflate them:
+
+- `system` (default): the System VM guest kernel (`configs/arcbox-{arch}.config`,
+  artifact `kernel-{arch}`). Full container stack: netfilter, cgroups
+  controllers, dm, overlayfs, NFS, HZ=1000/voluntary (ABX-498 tuning).
+- `microvm`: the Firecracker sandbox guest kernel
+  (`configs/arcbox-microvm-arm64.config`, artifact `microvm-kernel-arm64`,
+  arm64-only). Runs NESTED inside the System VM; optimized for kernel entry
+  → `/sbin/vm-agent` in the 200–300 ms class. virtio-mmio only — no
+  PCI/ACPI/EFI/netfilter/BPF; HZ=100/PREEMPT_NONE (nested ticks are
+  expensive). Consumed by boot-assets `upstream.toml` as the `vmlinux`
+  binary (`install_dir = "kernel"`).
+
+A flavor's load-bearing symbols are asserted post-`olddefconfig` in
+`scripts/build-kernel.sh` — extend the flavor's assertion list when adding a
+symbol whose silent loss would only surface at guest runtime.
+
 ## Build Commands
 
 ```bash
@@ -15,6 +32,9 @@ This file provides guidance to Claude Code (claude.ai/code) when working with co
 # Build kernel for x86_64
 ARCH=x86_64 ./scripts/build-kernel.sh
 
+# Build the Firecracker sandbox microVM kernel (arm64-only)
+FLAVOR=microvm ./scripts/build-kernel.sh
+
 # Build kernel with specific version
 KERNEL_VERSION=6.18.0 ./scripts/build-kernel.sh
 
@@ -44,8 +64,9 @@ cargo build -p arcbox-agent --target aarch64-unknown-linux-musl --release
 ```
 arcbox-kernel/
 ├── configs/
-│   ├── arcbox-arm64.config     # ARM64 kernel config (Apple Silicon)
-│   └── arcbox-x86_64.config    # x86_64 kernel config
+│   ├── arcbox-arm64.config           # ARM64 System VM config (Apple Silicon)
+│   ├── arcbox-x86_64.config          # x86_64 System VM config
+│   └── arcbox-microvm-arm64.config   # ARM64 Firecracker sandbox config
 ├── scripts/
 │   ├── build-kernel.sh         # Kernel build (Docker-based)
 │   ├── build-initramfs.sh      # Initramfs build (Alpine + agent)
diff --git a/README.md b/README.md
index 4f1db07..372354c 100644
--- a/README.md
+++ b/README.md
@@ -9,6 +9,25 @@ This repository contains:
 - Build scripts for kernel and initramfs
 - GitHub Actions CI for automated releases
 
+## Kernel Flavors
+
+Two independent guest kernels are built from the same kernel source:
+
+| Flavor | Config | Artifact | Boots |
+|--------|--------|----------|-------|
+| `system` (default) | `configs/arcbox-{arch}.config` | `kernel-{arch}` | ArcBox System VM (VZ/HV backends) |
+| `microvm` | `configs/arcbox-microvm-arm64.config` | `microvm-kernel-arm64` | Firecracker sandbox microVMs, nested inside the System VM |
+
+The microvm flavor is arm64-only for now: Firecracker x86_64 boots an ELF
+`vmlinux` (not a bzImage) and needs its own config
+(`VIRTIO_MMIO_CMDLINE_DEVICES`, kvmclock). It targets kernel entry →
+PID 1 in the 200–300 ms class under nested virtualization: virtio-mmio
+device model only, no PCI/ACPI/EFI/netfilter, everything built in.
+
+```bash
+FLAVOR=microvm ./scripts/build-kernel.sh
+```
+
 ## Features
 
 | Feature | Description |
@@ -49,8 +68,9 @@ tar -xzf arcbox-kernel-arm64-v0.1.0.tar.gz
 ```
 arcbox-kernel/
 ├── configs/
-│   ├── arcbox-arm64.config     # ARM64 kernel config
-│   └── arcbox-x86_64.config    # x86_64 kernel config
+│   ├── arcbox-arm64.config           # ARM64 System VM kernel config
+│   ├── arcbox-x86_64.config          # x86_64 System VM kernel config
+│   └── arcbox-microvm-arm64.config   # ARM64 Firecracker sandbox kernel config
 ├── scripts/
 │   ├── build-kernel.sh         # Kernel build script
 │   ├── build-initramfs.sh      # Initramfs build script
diff --git a/configs/arcbox-microvm-arm64.config b/configs/arcbox-microvm-arm64.config
new file mode 100644
index 0000000..5a7f69a
--- /dev/null
+++ b/configs/arcbox-microvm-arm64.config
@@ -0,0 +1,252 @@
+# ArcBox microVM (sandbox) kernel configuration for ARM64
+#
+# Guest kernel for Firecracker sandbox microVMs, which run NESTED inside the
+# ArcBox System VM (KVM inside a VZ guest on Apple Silicon).
+#
+# Optimized for:
+# - kernel entry -> /sbin/vm-agent (PID 1) in ~200-300 ms under nested virt
+# - Firecracker aarch64 device model only: virtio-mmio via DT, 16550 UART
+#   (ttyS0), PL031 RTC, GICv3, PSCI — no PCI, no ACPI, no EFI
+# - plain ext4 rootfs over virtio-blk (dm-snapshot CoW lives in the System
+#   VM, the microVM sees an ordinary block device)
+# - arbitrary user workloads from Docker-image templates (busybox userland,
+#   node/python/etc.) driven by vm-agent's vsock exec/PTY protocol
+# - Firecracker memory snapshot/restore (transparent to the guest; VMGenID
+#   reseeds the RNG in restored clones; ptp_kvm + PL031 give the guest a
+#   host-clock source for post-restore wall-time resync, CORE-75)
+#
+# Everything built in; CONFIG_MODULES stays off. Fragment style matches
+# configs/arcbox-arm64.config: copied to .config, resolved by olddefconfig,
+# then asserted by scripts/build-kernel.sh (microvm assertion set).
+# EXPERT is required to expose the VT/INPUT/... disables below.
+
+# Basic setup
+CONFIG_LOCALVERSION="-arcbox-microvm"
+CONFIG_DEFAULT_HOSTNAME="arcbox-sandbox"
+CONFIG_EXPERT=y
+CONFIG_IKCONFIG=y
+CONFIG_IKCONFIG_PROC=y
+# CONFIG_MODULES is not set
+
+# Processor type and features
+CONFIG_ARM64=y
+CONFIG_64BIT=y
+CONFIG_MMU=y
+CONFIG_SMP=y
+CONFIG_NR_CPUS=32
+# Firecracker never hotplugs vCPUs, and dropping HOTPLUG_CPU removes the
+# cpuhp state machinery from boot.
+# CONFIG_HOTPLUG_CPU is not set
+# Apple Silicon cores have no AArch32 EL0, so 32-bit compat is dead weight
+# (and vdso32 would need a separate 32-bit toolchain).
+# CONFIG_COMPAT is not set
+# The sandbox never hosts further guests; KVM init has no business here.
+# CONFIG_VIRTUALIZATION is not set
+
+# Core syscall surface for arbitrary workloads. Several of these are
+# EXPERT-gated defaults; stated explicitly so a Kconfig default change can
+# never silently drop them.
+CONFIG_MULTIUSER=y
+CONFIG_SYSVIPC=y
+CONFIG_POSIX_MQUEUE=y
+CONFIG_POSIX_TIMERS=y
+CONFIG_FUTEX=y
+CONFIG_EPOLL=y
+CONFIG_SIGNALFD=y
+CONFIG_TIMERFD=y
+CONFIG_EVENTFD=y
+CONFIG_AIO=y
+CONFIG_IO_URING=y
+CONFIG_ADVISE_SYSCALLS=y
+CONFIG_MEMBARRIER=y
+CONFIG_RSEQ=y
+CONFIG_SHMEM=y
+CONFIG_KALLSYMS=y
+CONFIG_ELF_CORE=y
+CONFIG_COREDUMP=y
+CONFIG_BINFMT_ELF=y
+CONFIG_BINFMT_SCRIPT=y
+
+# Timing / scheduler: HZ=100 + NO_HZ_IDLE + PREEMPT_NONE match the
+# Firecracker CI kernel the 15 ms warm-exec number was measured on; nested
+# timer ticks are expensive (each L2 tick is an L1 KVM arch-timer
+# injection), so keep them rare. This deliberately differs from the System
+# VM kernel's HZ=1000/voluntary (ABX-498): that guest churns containers,
+# this one runs a single workload.
+CONFIG_HIGH_RES_TIMERS=y
+CONFIG_NO_HZ_IDLE=y
+CONFIG_HZ_100=y
+CONFIG_HZ=100
+CONFIG_PREEMPT_NONE=y
+# PSI taxes the scheduler wakeup fast path (ABX-498); nothing in the
+# microVM consumes /proc/pressure.
+# CONFIG_PSI is not set
+
+# Isolation primitives workloads actually use: Chromium/Puppeteer sandboxes
+# need USER_NS + seccomp; language runtimes probe /proc/self/cgroup (core
+# cgroups only, no controllers — a sandbox is a single workload, memory
+# limiting is VM sizing).
+CONFIG_NAMESPACES=y
+CONFIG_USER_NS=y
+CONFIG_PID_NS=y
+CONFIG_NET_NS=y
+CONFIG_IPC_NS=y
+CONFIG_UTS_NS=y
+CONFIG_TIME_NS=y
+CONFIG_SECCOMP=y
+CONFIG_SECCOMP_FILTER=y
+CONFIG_CGROUPS=y
+
+# Boot-time fat from the Firecracker CI kernel, explicitly OFF
+# CONFIG_AUDIT is not set
+# CONFIG_PROFILING is not set
+# CONFIG_BPF_SYSCALL is not set
+# CONFIG_KEXEC is not set
+# CONFIG_KEXEC_FILE is not set
+# CONFIG_CRASH_DUMP is not set
+# CONFIG_EFI is not set
+# CONFIG_ACPI is not set
+# CONFIG_PCI is not set
+# CONFIG_NUMA is not set
+# CONFIG_SWAP is not set
+# CONFIG_SUSPEND is not set
+# CONFIG_HIBERNATION is not set
+# CONFIG_PM is not set
+# CONFIG_CPU_IDLE is not set
+# CONFIG_CPU_FREQ is not set
+# CONFIG_RANDOMIZE_BASE is not set
+# CONFIG_IOMMU_SUPPORT is not set
+# CONFIG_VT is not set
+# CONFIG_INPUT is not set
+# CONFIG_HID_SUPPORT is not set
+# CONFIG_USB_SUPPORT is not set
+# CONFIG_SOUND is not set
+# CONFIG_WLAN is not set
+# CONFIG_WIRELESS is not set
+# CONFIG_RFKILL is not set
+# CONFIG_DEBUG_FS is not set
+# CONFIG_FTRACE is not set
+# CONFIG_LOCKUP_DETECTOR is not set
+# CONFIG_DETECT_HUNG_TASK is not set
+# CONFIG_SCHED_DEBUG is not set
+CONFIG_MAGIC_SYSRQ=y
+CONFIG_JUMP_LABEL=y
+
+# Memory management. THP=madvise: opt-in for workloads that ask, without
+# khugepaged churning snapshot dirty-page sets in the background.
+CONFIG_TRANSPARENT_HUGEPAGE=y
+CONFIG_TRANSPARENT_HUGEPAGE_MADVISE=y
+# CONFIG_MEMORY_HOTPLUG is not set
+# CONFIG_ZSWAP is not set
+
+# Networking. Static addressing comes from the kernel ip= parameter that
+# arcbox-vm/sandbox/boot.rs appends (ip=<client>::<gw>:<mask>::eth0:off),
+# handled by IP_PNP; the autoconf protocols are never used. NAT/firewalling
+# for sandboxes happens in the System VM (L1) — vm-agent uses raw
+# SIOCSIFADDR/SIOCADDRT ioctls, no iptables in the microVM.
+CONFIG_NET=y
+CONFIG_PACKET=y
+CONFIG_UNIX=y
+CONFIG_INET=y
+CONFIG_IP_PNP=y
+# CONFIG_IP_PNP_DHCP is not set
+# CONFIG_IP_PNP_BOOTP is not set
+# CONFIG_IP_PNP_RARP is not set
+CONFIG_IPV6=y
+# CONFIG_NETFILTER is not set
+# CONFIG_BRIDGE is not set
+CONFIG_VSOCKETS=y
+CONFIG_VIRTIO_VSOCKETS=y
+
+# Firecracker device model. NETDEVICES/NET_CORE are NOT default-on: without
+# them olddefconfig silently drops VIRTIO_NET (the exact silent-degrade
+# class the build assertions exist for). ETHERNET is the vendor-NIC
+# umbrella; virtio-net does not need it.
+CONFIG_BLOCK=y
+CONFIG_BLK_DEV=y
+CONFIG_NETDEVICES=y
+CONFIG_NET_CORE=y
+# CONFIG_ETHERNET is not set
+CONFIG_VIRTIO=y
+CONFIG_VIRTIO_MENU=y
+CONFIG_VIRTIO_MMIO=y
+CONFIG_VIRTIO_BLK=y
+CONFIG_VIRTIO_NET=y
+# Balloon: the only memory-reclaim lever Firecracker offers; kept built-in
+# so a future reclaim feature (and snapshots that include a balloon device)
+# need no kernel change. Costs nothing at boot when the device is absent.
+CONFIG_VIRTIO_BALLOON=y
+CONFIG_HW_RANDOM=y
+CONFIG_HW_RANDOM_VIRTIO=y
+CONFIG_HW_RANDOM_ARM_SMCCC_TRNG=y
+CONFIG_TTY=y
+CONFIG_SERIAL_8250=y
+CONFIG_SERIAL_8250_CONSOLE=y
+CONFIG_SERIAL_8250_NR_UARTS=1
+CONFIG_SERIAL_8250_RUNTIME_UARTS=1
+CONFIG_SERIAL_OF_PLATFORM=y
+CONFIG_SERIAL_EARLYCON=y
+CONFIG_UNIX98_PTYS=y
+CONFIG_DEVPTS_FS=y
+# CONFIG_LEGACY_PTYS is not set
+# The default sandbox rootfs ships an EMPTY /dev; without the devtmpfs
+# automount PID 1 has no /dev/console for stdio (vm-agent mounts /dev
+# itself, but only after its fds are already bound).
+CONFIG_DEVTMPFS=y
+CONFIG_DEVTMPFS_MOUNT=y
+# Firecracker boots the root directly from virtio-blk; there is no
+# initramfs stage.
+# CONFIG_BLK_DEV_INITRD is not set
+
+# Time: cold-boot wall clock + post-restore resync (CORE-75). Firecracker
+# aarch64 exposes a PL031 RTC backed by the L1 host clock: RTC_HCTOSYS sets
+# CLOCK_REALTIME at cold boot with no host RPC; RTC_INTF_DEV lets vm-agent
+# RTC_RD_TIME-resync (seconds granularity) after restore. ptp_kvm exposes
+# the L1 host CLOCK_REALTIME at ns granularity via the KVM SMCCC vendor
+# service (/dev/ptp0) for a precise one-shot resync. SYSTOHC stays off: the
+# virtual RTC mirrors the host clock, the guest must not write back into
+# it. (PTP_1588_CLOCK_VMCLOCK is deliberately absent: it depends on ACPI,
+# which this config cuts, and Firecracker presents no vmclock device.)
+CONFIG_RTC_CLASS=y
+CONFIG_RTC_HCTOSYS=y
+CONFIG_RTC_HCTOSYS_DEVICE="rtc0"
+CONFIG_RTC_INTF_DEV=y
+CONFIG_RTC_DRV_PL031=y
+# CONFIG_RTC_SYSTOHC is not set
+CONFIG_PTP_1588_CLOCK=y
+CONFIG_PTP_1588_CLOCK_KVM=y
+# Steal-time accounting is inert until Firecracker configures KVM pvtime,
+# but PARAVIRT is cheap and future-proofs it.
+CONFIG_PARAVIRT=y
+CONFIG_PARAVIRT_TIME_ACCOUNTING=y
+# DT-based VMGenID (kernel >= 6.10): reseeds the guest RNG when a restored
+# clone diverges from its snapshot origin. VIRT_DRIVERS is the (default-off)
+# menu gate it lives under.
+CONFIG_VIRT_DRIVERS=y
+CONFIG_VMGENID=y
+
+# File systems. ext4 only: template rootfs images are flattened ext4
+# (oci2rootfs); the dm-snapshot CoW layer lives outside the microVM. No
+# overlayfs consumer exists inside the microVM today (verified against
+# rootfs_builder.rs and the sandbox boot path).
+CONFIG_EXT4_FS=y
+CONFIG_EXT4_FS_POSIX_ACL=y
+CONFIG_EXT4_FS_SECURITY=y
+CONFIG_PROC_FS=y
+CONFIG_PROC_SYSCTL=y
+CONFIG_SYSFS=y
+CONFIG_TMPFS=y
+CONFIG_TMPFS_POSIX_ACL=y
+CONFIG_TMPFS_XATTR=y
+CONFIG_INOTIFY_USER=y
+CONFIG_FANOTIFY=y
+CONFIG_FILE_LOCKING=y
+# CONFIG_OVERLAY_FS is not set
+# CONFIG_FUSE_FS is not set
+# CONFIG_BLK_DEV_LOOP is not set
+# CONFIG_QUOTA is not set
+
+# Crypto (ext4 metadata checksums)
+CONFIG_CRYPTO=y
+CONFIG_CRYPTO_CRC32C=y
+CONFIG_CRC32=y
diff --git a/scripts/build-kernel.sh b/scripts/build-kernel.sh
index f64b3fe..73346dc 100755
--- a/scripts/build-kernel.sh
+++ b/scripts/build-kernel.sh
@@ -2,9 +2,17 @@
 # Build Linux kernel for ArcBox
 #
 # Usage:
-#   ./build-kernel.sh                    # Build for ARM64
+#   ./build-kernel.sh                    # Build System VM kernel for ARM64
 #   ARCH=x86_64 ./build-kernel.sh        # Build for x86_64
+#   FLAVOR=microvm ./build-kernel.sh     # Build the sandbox microVM kernel
 #   KERNEL_VERSION=6.18.0 ./build-kernel.sh  # Use specific version
+#
+# Flavors:
+#   system  (default) — System VM guest kernel (VZ/HV backends),
+#                       configs/arcbox-{arch}.config, output kernel-{arch}
+#   microvm           — Firecracker sandbox guest kernel (arm64 only),
+#                       configs/arcbox-microvm-{arch}.config,
+#                       output microvm-kernel-{arch}
 
 set -e
 
@@ -14,16 +22,15 @@ PROJECT_DIR="$(dirname "$SCRIPT_DIR")"
 # Configuration
 KERNEL_VERSION="${KERNEL_VERSION:-6.18.38}"
 TARGET_ARCH="${ARCH:-arm64}"
+FLAVOR="${FLAVOR:-system}"
 OUTPUT_DIR="${OUTPUT_DIR:-$PROJECT_DIR/output}"
 CONFIG_DIR="$PROJECT_DIR/configs"
 
-# Determine config file
+# Determine architecture parameters
 if [ "$TARGET_ARCH" = "arm64" ]; then
-    CONFIG_FILE="$CONFIG_DIR/arcbox-arm64.config"
     CROSS_COMPILE="aarch64-linux-gnu-"
     KERNEL_IMAGE="Image"
 elif [ "$TARGET_ARCH" = "x86_64" ]; then
-    CONFIG_FILE="$CONFIG_DIR/arcbox-x86_64.config"
     CROSS_COMPILE=""
     KERNEL_IMAGE="bzImage"
 else
@@ -31,12 +38,58 @@ else
     exit 1
 fi
 
+# Determine flavor parameters: config file, output name, and the post-
+# olddefconfig assertion sets. olddefconfig silently drops unknown or
+# unsatisfiable symbols; each flavor asserts its load-bearing ones actually
+# resolved (a renamed choice symbol or a new dependency gate in the fragment
+# otherwise degrades silently — 6.18 did exactly that to the legacy iptables
+# stack via NETFILTER_XTABLES_LEGACY).
+if [ "$FLAVOR" = "system" ]; then
+    CONFIG_FILE="$CONFIG_DIR/arcbox-$TARGET_ARCH.config"
+    OUTPUT_NAME="kernel-$TARGET_ARCH"
+    # CONFIG_PREEMPT_VOLUNTARY is load-bearing for container-teardown
+    # latency (see the config comment); a future KERNEL_VERSION that drops
+    # the voluntary choice must fail loudly here rather than silently fall
+    # back to lazy/full.
+    ASSERT_Y="CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU CONFIG_IP_NF_NAT
+              CONFIG_IP6_NF_NAT CONFIG_HZ_1000 CONFIG_PSI_DEFAULT_DISABLED
+              CONFIG_PREEMPT_VOLUNTARY"
+    ASSERT_N=""
+elif [ "$FLAVOR" = "microvm" ]; then
+    if [ "$TARGET_ARCH" != "arm64" ]; then
+        echo "Error: microvm flavor is arm64-only (Firecracker x86_64 needs an ELF vmlinux and a separate config)"
+        exit 1
+    fi
+    CONFIG_FILE="$CONFIG_DIR/arcbox-microvm-$TARGET_ARCH.config"
+    OUTPUT_NAME="microvm-kernel-$TARGET_ARCH"
+    # The Firecracker sandbox contract: virtio-mmio devices, vsock exec/PTY,
+    # devtmpfs automount over the empty template /dev, static ip=, PL031 +
+    # ptp_kvm clocks, VMGenID RNG reseed. Also assert that the deliberately
+    # cut subsystems stayed cut (a fragment typo re-enabling PCI/netfilter
+    # would otherwise ship silently).
+    ASSERT_Y="CONFIG_VIRTIO_MMIO CONFIG_VIRTIO_BLK CONFIG_VIRTIO_NET
+              CONFIG_VIRTIO_VSOCKETS CONFIG_DEVTMPFS_MOUNT CONFIG_IP_PNP
+              CONFIG_UNIX98_PTYS CONFIG_EXT4_FS CONFIG_SERIAL_8250_CONSOLE
+              CONFIG_RTC_DRV_PL031 CONFIG_PTP_1588_CLOCK_KVM CONFIG_VMGENID"
+    ASSERT_N="CONFIG_PCI CONFIG_NETFILTER CONFIG_MODULES CONFIG_ACPI CONFIG_EFI"
+else
+    echo "Error: Unsupported flavor: $FLAVOR (expected 'system' or 'microvm')"
+    exit 1
+fi
+
+# Collapse the multi-line assertion lists to one line: they are textually
+# interpolated into the Docker build script, where an embedded newline would
+# terminate the `for ... in` list early.
+ASSERT_Y=$(echo $ASSERT_Y)
+ASSERT_N=$(echo $ASSERT_N)
+
 echo "========================================"
 echo "  ArcBox Kernel Build"
 echo "========================================"
 echo ""
 echo "  Kernel Version: $KERNEL_VERSION"
 echo "  Target Arch:    $TARGET_ARCH"
+echo "  Flavor:         $FLAVOR"
 echo "  Output Dir:     $OUTPUT_DIR"
 echo ""
 
@@ -56,6 +109,7 @@ mkdir -p "$OUTPUT_DIR"
 #   - CWD = extracted kernel source root (linux-$KERNEL_VERSION)
 #   - $ARCBOX_SRC = path to arcbox-kernel repo
 #   - $TARGET_ARCH, $KERNEL_IMAGE, $CROSS_COMPILE set
+#   - $CONFIG_FILE, $ASSERT_Y, $ASSERT_N set (flavor-resolved above)
 #   - $OUTPUT_PATH = where to copy the final kernel binary
 do_build() {
     local ARCBOX_SRC="$1"
@@ -65,30 +119,21 @@ do_build() {
     sh "$ARCBOX_SRC/scripts/inject-drivers.sh" "$ARCBOX_SRC"
 
     # Copy config and update for this kernel version.
-    cp "$ARCBOX_SRC/configs/arcbox-$TARGET_ARCH.config" .config
+    cp "$CONFIG_FILE" .config
     make ARCH=$TARGET_ARCH ${CROSS_COMPILE:+CROSS_COMPILE=$CROSS_COMPILE} olddefconfig
 
-    # olddefconfig silently drops unknown or unsatisfiable symbols; assert the
-    # load-bearing ones actually resolved (a renamed choice symbol or a new
-    # dependency gate in the fragment otherwise degrades silently — 6.18 did
-    # exactly that to the legacy iptables stack via NETFILTER_XTABLES_LEGACY).
-    for sym in CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU CONFIG_IP_NF_NAT \
-               CONFIG_IP6_NF_NAT CONFIG_HZ_1000 \
-               CONFIG_PSI_DEFAULT_DISABLED; do
+    for sym in $ASSERT_Y; do
         grep -q "^$sym=y" .config || {
             echo "ERROR: $sym missing after olddefconfig" >&2
             exit 1
         }
     done
-
-    # Voluntary preemption is load-bearing for container-teardown latency
-    # (see the config comment). Assert it survived olddefconfig; a future
-    # KERNEL_VERSION that drops the voluntary choice must fail loudly here
-    # rather than silently fall back to lazy/full.
-    grep -q '^CONFIG_PREEMPT_VOLUNTARY=y' .config || {
-        echo 'ERROR: CONFIG_PREEMPT_VOLUNTARY missing after olddefconfig' >&2
-        exit 1
-    }
+    for sym in $ASSERT_N; do
+        if grep -q "^$sym=y" .config; then
+            echo "ERROR: $sym enabled after olddefconfig (must stay off)" >&2
+            exit 1
+        fi
+    done
 
     # Build.
     echo "Building kernel..."
@@ -113,6 +158,9 @@ else
 fi
 
 if [ "$BUILD_IN_DOCKER" = "1" ]; then
+    # $ASSERT_Y/$ASSERT_N/$OUTPUT_NAME and the config basename are expanded
+    # host-side into the container script, so both paths share one
+    # flavor-resolution.
     docker run --rm \
         -v "$PROJECT_DIR:/workspace" \
         -v "$OUTPUT_DIR:/output" \
@@ -127,23 +175,25 @@ curl -L --retry 8 --retry-all-errors -o linux.tar.xz https://cdn.kernel.org/pub/
 tar -xJf linux.tar.xz && rm linux.tar.xz
 cd linux-$KERNEL_VERSION
 sh /workspace/scripts/inject-drivers.sh /workspace
-cp /workspace/configs/arcbox-$TARGET_ARCH.config .config
+cp /workspace/configs/$(basename "$CONFIG_FILE") .config
 make ARCH=$TARGET_ARCH olddefconfig
-for sym in CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU CONFIG_IP_NF_NAT CONFIG_IP6_NF_NAT CONFIG_HZ_1000 CONFIG_PSI_DEFAULT_DISABLED; do
+for sym in $ASSERT_Y; do
     grep -q \"^\$sym=y\" .config || {
         echo \"ERROR: \$sym missing after olddefconfig\" >&2
         exit 1
     }
 done
-grep -q '^CONFIG_PREEMPT_VOLUNTARY=y' .config || {
-    echo 'ERROR: CONFIG_PREEMPT_VOLUNTARY missing after olddefconfig' >&2
-    exit 1
-}
+for sym in $ASSERT_N; do
+    if grep -q \"^\$sym=y\" .config; then
+        echo \"ERROR: \$sym enabled after olddefconfig (must stay off)\" >&2
+        exit 1
+    fi
+done
 echo 'Building kernel...'
 make ARCH=$TARGET_ARCH -j\$(nproc) $KERNEL_IMAGE
-cp arch/$TARGET_ARCH/boot/$KERNEL_IMAGE /output/kernel-$TARGET_ARCH
+cp arch/$TARGET_ARCH/boot/$KERNEL_IMAGE /output/$OUTPUT_NAME
 echo 'Build complete!'
-ls -lh /output/kernel-$TARGET_ARCH
+ls -lh /output/$OUTPUT_NAME
 "
 else
     BUILD_DIR="/tmp/arcbox-kernel-build-$$"
@@ -157,7 +207,7 @@ else
     rm "linux.tar.xz"
     cd "linux-$KERNEL_VERSION"
 
-    do_build "$PROJECT_DIR" "$OUTPUT_DIR/kernel-$TARGET_ARCH"
+    do_build "$PROJECT_DIR" "$OUTPUT_DIR/$OUTPUT_NAME"
 
     rm -rf "$BUILD_DIR"
 fi
@@ -167,5 +217,5 @@ echo "========================================"
 echo "  Build Complete!"
 echo "========================================"
 echo ""
-echo "  Output: $OUTPUT_DIR/kernel-$TARGET_ARCH"
-ls -lh "$OUTPUT_DIR/kernel-$TARGET_ARCH"
+echo "  Output: $OUTPUT_DIR/$OUTPUT_NAME"
+ls -lh "$OUTPUT_DIR/$OUTPUT_NAME"
diff --git a/scripts/package-release.sh b/scripts/package-release.sh
index 4f64d83..a4ffadc 100755
--- a/scripts/package-release.sh
+++ b/scripts/package-release.sh
@@ -30,18 +30,18 @@ echo ""
 rm -rf "$RELEASE_DIR"
 mkdir -p "$RELEASE_DIR"
 
-for ARCH in arm64 x86_64; do
-    KERNEL="$OUTPUT_DIR/kernel-$ARCH"
+for NAME in kernel-arm64 kernel-x86_64 microvm-kernel-arm64; do
+    KERNEL="$OUTPUT_DIR/$NAME"
 
     if [ ! -f "$KERNEL" ]; then
-        echo "Warning: kernel-$ARCH not found, skipping"
+        echo "Warning: $NAME not found, skipping"
         continue
     fi
 
-    echo "Packaging $ARCH..."
-    cp "$KERNEL" "$RELEASE_DIR/kernel-$ARCH"
-    sha256sum "$RELEASE_DIR/kernel-$ARCH" > "$RELEASE_DIR/kernel-$ARCH.sha256"
-    echo "  Created: kernel-$ARCH + kernel-$ARCH.sha256"
+    echo "Packaging $NAME..."
+    cp "$KERNEL" "$RELEASE_DIR/$NAME"
+    sha256sum "$RELEASE_DIR/$NAME" > "$RELEASE_DIR/$NAME.sha256"
+    echo "  Created: $NAME + $NAME.sha256"
 done
 
 echo ""
@@ -50,4 +50,4 @@ echo "  Packaging Complete!"
 echo "========================================"
 echo ""
 echo "Release files:"
-ls -lh "$RELEASE_DIR"/kernel-* 2>/dev/null || echo "  (none)"
+ls -lh "$RELEASE_DIR"/*kernel-* 2>/dev/null || echo "  (none)"