diff --git a/ex_engine/build_moe_topk.sh b/ex_engine/build_moe_topk.sh
new file mode 100755
index 00000000..5d41da85
--- /dev/null
+++ b/ex_engine/build_moe_topk.sh
@@ -0,0 +1,48 @@
+#!/usr/bin/env bash
+# build_moe_topk.sh — Compile moe_topk_softmax_v3.cu into importable .so
+set -euo pipefail
+cd "$(dirname "$0")"
+
+PYTHON=${PYTHON:-python3}
+TORCH_ROOT=$($PYTHON -c "import torch; import os; print(os.path.dirname(torch.__file__))")
+PY_INC=$($PYTHON -c "import sysconfig; print(sysconfig.get_path('include'))")
+PY_SUFFIX=$($PYTHON -c "import sysconfig; print(sysconfig.get_config_var('EXT_SUFFIX'))")
+TORCH_INC="${TORCH_ROOT}/include"
+TORCH_INC2="${TORCH_ROOT}/include/torch/csrc/api/include"
+TORCH_LIB="${TORCH_ROOT}/lib"
+
+for _CXX in /usr/local/corex/bin/clang++ g++; do
+    [ -x "$_CXX" ] && CXX="$_CXX" && break
+done
+
+mkdir -p build
+OUT="build/moe_topk_softmax_v3${PY_SUFFIX}"
+
+echo "[build] CXX=$CXX"
+echo "[build] Output: $OUT"
+
+$CXX -shared -fPIC -O2 -std=c++17 \
+    --cuda-gpu-arch=ivcore10 \
+    -I"$PY_INC" \
+    -I"$TORCH_INC" \
+    -I"$TORCH_INC2" \
+    -L"$TORCH_LIB" \
+    -ltorch -ltorch_cpu -ltorch_cuda -lc10 -lc10_cuda \
+    -Wl,--no-as-needed,-rpath,"$TORCH_LIB" \
+    -D_GLIBCXX_USE_CXX11_ABI=0 \
+    -DTORCH_EXTENSION_NAME=moe_topk_softmax_v3 \
+    csrc/moe_topk_softmax_v3.cu \
+    -o "$OUT" 2>&1
+
+echo "[build] Size: $(du -h "$OUT" | cut -f1)"
+
+# Verify import + GPU test
+$PYTHON << PY
+import importlib.util, torch
+spec = importlib.util.spec_from_file_location("moe_topk_softmax_v3", "$OUT")
+mod = importlib.util.module_from_spec(spec)
+spec.loader.exec_module(mod)
+g = torch.randn(4, 64, device="cuda", dtype=torch.float16)
+w, ids, src = mod.moe_topk_softmax(g, 8, True)
+print(f"[verify] ✓ weights={w.shape} ids={ids.shape} sum={w.sum(-1).tolist()}")
+PY