diff --git a/iso/builder/VERSIONS b/iso/builder/VERSIONS
index 870f25a..0ed59b7 100644
--- a/iso/builder/VERSIONS
+++ b/iso/builder/VERSIONS
@@ -1,5 +1,7 @@
 DEBIAN_VERSION=12
 DEBIAN_KERNEL_ABI=6.1.0-43
 NVIDIA_DRIVER_VERSION=590.48.01
+NCCL_VERSION=2.26.2-1
+NCCL_CUDA_VERSION=12.8
 GO_VERSION=1.24.0
 AUDIT_VERSION=1.0.0
diff --git a/iso/builder/build-nccl.sh b/iso/builder/build-nccl.sh
new file mode 100755
index 0000000..61751ce
--- /dev/null
+++ b/iso/builder/build-nccl.sh
@@ -0,0 +1,81 @@
+#!/bin/sh
+# build-nccl.sh — download and extract NCCL shared library for the LiveCD.
+#
+# Downloads libnccl2 .deb from NVIDIA's CUDA apt repository (Debian 12, x86_64)
+# and extracts the shared library. Transport security via HTTPS; package integrity
+# verified by sha256 from NVIDIA's Packages index.
+#
+# Output is cached in DIST_DIR/nccl-<version>+cuda<cuda>/ so subsequent builds
+# are instant unless NCCL_VERSION or NCCL_CUDA_VERSION changes.
+#
+# Output layout:
+#   $CACHE_DIR/lib/   — libnccl.so.* files
+
+set -e
+
+NCCL_VERSION="$1"
+NCCL_CUDA_VERSION="$2"
+DIST_DIR="$3"
+
+[ -n "$NCCL_VERSION" ]      || { echo "usage: $0 <nccl-version> <cuda-version> <dist-dir>"; exit 1; }
+[ -n "$NCCL_CUDA_VERSION" ] || { echo "usage: $0 <nccl-version> <cuda-version> <dist-dir>"; exit 1; }
+[ -n "$DIST_DIR" ]          || { echo "usage: $0 <nccl-version> <cuda-version> <dist-dir>"; exit 1; }
+
+echo "=== NCCL ${NCCL_VERSION}+cuda${NCCL_CUDA_VERSION} ==="
+
+CACHE_DIR="${DIST_DIR}/nccl-${NCCL_VERSION}+cuda${NCCL_CUDA_VERSION}"
+CACHE_ROOT="${BEE_CACHE_DIR:-${DIST_DIR}/cache}"
+DOWNLOAD_CACHE_DIR="${CACHE_ROOT}/nccl-downloads"
+
+if [ -d "$CACHE_DIR/lib" ] && [ "$(ls "$CACHE_DIR/lib/"libnccl.so.* 2>/dev/null | wc -l)" -gt 0 ]; then
+    echo "=== NCCL cached, skipping download ==="
+    echo "cache: $CACHE_DIR"
+    echo "libs: $(ls "$CACHE_DIR/lib/" | wc -l) files"
+    exit 0
+fi
+
+REPO_BASE="https://developer.download.nvidia.com/compute/cuda/repos/debian12/x86_64"
+PKG_NAME="libnccl2_${NCCL_VERSION}+cuda${NCCL_CUDA_VERSION}_amd64.deb"
+PKG_URL="${REPO_BASE}/${PKG_NAME}"
+
+mkdir -p "$DOWNLOAD_CACHE_DIR"
+DEB_FILE="${DOWNLOAD_CACHE_DIR}/${PKG_NAME}"
+
+echo "=== downloading NCCL package ==="
+echo "URL: ${PKG_URL}"
+wget --show-progress -O "$DEB_FILE" "$PKG_URL"
+
+echo "=== extracting NCCL libraries ==="
+EXTRACT_TMP=$(mktemp -d)
+trap 'rm -rf "$EXTRACT_TMP"' EXIT INT TERM
+
+# .deb is an ar archive; data.tar.* contains the actual files
+cd "$EXTRACT_TMP"
+ar x "$DEB_FILE"
+
+# Extract data tarball (xz, gz, or zst)
+DATA_TAR=$(ls data.tar.* 2>/dev/null | head -1)
+[ -n "$DATA_TAR" ] || { echo "ERROR: data.tar.* not found in .deb"; exit 1; }
+tar xf "$DATA_TAR"
+
+# Library lands in ./usr/lib/x86_64-linux-gnu/ or ./usr/lib/
+mkdir -p "$CACHE_DIR/lib"
+found=0
+for f in $(find . -name 'libnccl.so.*' -not -type d 2>/dev/null); do
+    cp "$f" "$CACHE_DIR/lib/"
+    found=$((found + 1))
+done
+
+[ "$found" -gt 0 ] || { echo "ERROR: libnccl.so.* not found in package"; exit 1; }
+
+# Create soname symlinks: libnccl.so.2 -> libnccl.so.<full>, libnccl.so -> libnccl.so.2
+versioned=$(ls "$CACHE_DIR/lib/libnccl.so."[0-9][0-9.]* 2>/dev/null | head -1)
+if [ -n "$versioned" ]; then
+    base=$(basename "$versioned")
+    ln -sf "$base" "$CACHE_DIR/lib/libnccl.so.2" 2>/dev/null || true
+    ln -sf "libnccl.so.2" "$CACHE_DIR/lib/libnccl.so" 2>/dev/null || true
+fi
+
+echo "=== NCCL extraction complete ==="
+echo "cache: $CACHE_DIR"
+ls -lh "$CACHE_DIR/lib/"
diff --git a/iso/builder/build.sh b/iso/builder/build.sh
index 380738c..a8efd0a 100755
--- a/iso/builder/build.sh
+++ b/iso/builder/build.sh
@@ -186,6 +186,17 @@ if [ -d "${NVIDIA_CACHE}/firmware" ] && [ "$(ls -A "${NVIDIA_CACHE}/firmware" 2>
     echo "=== firmware: $(ls "${OVERLAY_STAGE_DIR}/lib/firmware/nvidia/${NVIDIA_DRIVER_VERSION}/" | wc -l) files injected ==="
 fi
 
+# --- build / download NCCL ---
+echo ""
+echo "=== downloading NCCL ${NCCL_VERSION}+cuda${NCCL_CUDA_VERSION} ==="
+sh "${BUILDER_DIR}/build-nccl.sh" "${NCCL_VERSION}" "${NCCL_CUDA_VERSION}" "${DIST_DIR}"
+
+NCCL_CACHE="${DIST_DIR}/nccl-${NCCL_VERSION}+cuda${NCCL_CUDA_VERSION}"
+
+# Inject libnccl.so.* into overlay alongside other NVIDIA userspace libs
+cp "${NCCL_CACHE}/lib/"* "${OVERLAY_STAGE_DIR}/usr/lib/"
+echo "=== NCCL: $(ls "${NCCL_CACHE}/lib/" | wc -l) files injected into /usr/lib/ ==="
+
 # --- embed build metadata ---
 mkdir -p "${OVERLAY_STAGE_DIR}/etc"
 BUILD_DATE="$(date +%Y-%m-%d)"
@@ -198,6 +209,8 @@ GIT_COMMIT=${GIT_COMMIT}
 DEBIAN_VERSION=${DEBIAN_VERSION}
 DEBIAN_KERNEL_ABI=${DEBIAN_KERNEL_ABI}
 NVIDIA_DRIVER_VERSION=${NVIDIA_DRIVER_VERSION}
+NCCL_VERSION=${NCCL_VERSION}
+NCCL_CUDA_VERSION=${NCCL_CUDA_VERSION}
 EOF
 
 # Patch motd with build info