diff --git a/test_se_multi_gpu.py b/test_se_multi_gpu.py
new file mode 100644
index 00000000..794c8f55
--- /dev/null
+++ b/test_se_multi_gpu.py
@@ -0,0 +1,68 @@
+#!/usr/bin/env python3
+"""Test: does the SE's L1 GEMM produce NaN on non-zero GPUs?"""
+import torch
+from dsv4.layers.shared_expert import Nvfp4SharedExpert
+
+torch.manual_seed(42)
+
+# Load a real checkpoint weight for layer 0's shared expert
+from safetensors.torch import load_file
+import json, os
+cdir = "/root/nvidia-meeting/DeepSeek-V4-Pro-NVFP4"
+
+# We'll use L0's weights and try running on different GPUs
+with open(os.path.join(cdir, "model.safetensors.index.json")) as f:
+    wmap = json.load(f)["weight_map"]
+
+# Load L0 SE weights
+shards_needed = set()
+for proj in ['gate_proj', 'up_proj', 'down_proj']:
+    k = f"model.layers.0.mlp.shared_experts.{proj}.weight"
+    if k in wmap:
+        shards_needed.add(wmap[k])
+
+all_w = {}
+for sn in shards_needed:
+    all_w.update(load_file(os.path.join(cdir, sn)))
+
+def get_weight(proj):
+    w = all_w.get(f"model.layers.0.mlp.shared_experts.{proj}.weight")
+    ws = all_w.get(f"model.layers.0.mlp.shared_experts.{proj}.weight_scale")
+    ws2 = all_w.get(f"model.layers.0.mlp.shared_experts.{proj}.weight_scale_2")
+    isc = all_w.get(f"model.layers.0.mlp.shared_experts.{proj}.input_scale")
+    return w, ws, ws2, isc
+
+for gpu in [0, 1]:
+    torch.cuda.set_device(gpu)
+    dev = f"cuda:{gpu}"
+    
+    se = Nvfp4SharedExpert(hidden_size=7168, intermediate_size=3072, device=dev)
+    
+    gw, gws, gws2, gisc = get_weight('gate_proj')
+    uw, uws, uws2, uisc = get_weight('up_proj')
+    dw, dws, dws2, disc = get_weight('down_proj')
+    
+    se.l1_fp4 = [torch.cat([gw, uw], dim=0).to(dev)]
+    se.l1_sf = [torch.cat([gws, uws], dim=0).to(dev)]
+    se.l1_gs = [1.0]
+    se.l1_ws2 = [gws2.to(dev) if gws2 is not None else None]
+    se._saved_l1_gsa = gisc.float().item()
+    
+    se.l2_fp4 = [dw.to(dev)]
+    se.l2_sf = [dws.to(dev)]
+    se.l2_gs = [1.0]
+    se.l2_ws2 = [dws2.to(dev) if dws2 is not None else None]
+    se._saved_l2_gsa = disc.float().item()
+    
+    # Run
+    x = torch.randn(1, 7168, dtype=torch.bfloat16, device=dev)
+    out = se.run(x)
+    
+    # Fix gsa
+    if hasattr(se, '_saved_l1_gsa'):
+        se._l1_activation_global_scale = se._saved_l1_gsa
+    if hasattr(se, '_saved_l2_gsa'):
+        se._l2_activation_global_scale = se._saved_l2_gsa
+    
+    has_nan = torch.isnan(out).any().item()
+    print(f"GPU {gpu}: |out|={out.abs().max().item() if not has_nan else 'NaN'} has_nan={has_nan} shape={out.shape}")