diff --git a/tests/test_ref_minimal.py b/tests/test_ref_minimal.py
new file mode 100644
index 00000000..937eb2ee
--- /dev/null
+++ b/tests/test_ref_minimal.py
@@ -0,0 +1,41 @@
+"""Minimal test: CUTLASS reference FMHA, n=256 only."""
+import sys
+sys.path.insert(0, '/root/cutlass/examples/python/CuTeDSL')
+
+import torch, math, cutlass, cutlass.cute as cute, cuda.bindings.driver as cuda
+from cute.blackwell.kernel.attention.fmha.fmha import BlackwellFusedMultiHeadAttentionForward, FMHA_OperandMajorMode
+
+HEAD_DIM = 64
+n = 256
+torch.manual_seed(42)
+m = 128; batch = 1
+q = torch.randn(batch, 1, m, HEAD_DIM, dtype=torch.bfloat16, device='cuda')
+k = torch.randn(batch, 1, n, HEAD_DIM, dtype=torch.bfloat16, device='cuda')
+v = torch.randn(batch, 1, n, HEAD_DIM, dtype=torch.bfloat16, device='cuda')
+c = torch.zeros(batch, 1, m, HEAD_DIM, dtype=torch.bfloat16, device='cuda')
+
+qf = q[0,0].float(); kf = k[0,0].float(); vf = v[0,0].float()
+scale = 1.0/math.sqrt(HEAD_DIM)
+ref = torch.softmax(qf @ kf.T * scale, dim=-1) @ vf
+
+stream = cuda.CUstream(torch.cuda.current_stream().cuda_stream)
+kernel = BlackwellFusedMultiHeadAttentionForward(
+    q_major_mode=FMHA_OperandMajorMode.K, k_major_mode=FMHA_OperandMajorMode.K,
+    v_major_mode=FMHA_OperandMajorMode.MN, o_major_mode=FMHA_OperandMajorMode.K,
+    q_head_dim=HEAD_DIM, kv_head_dim=HEAD_DIM, num_q_heads=1, num_kv_heads=1,
+    q_dtype=cutlass.BFloat16, k_dtype=cutlass.BFloat16, v_dtype=cutlass.BFloat16,
+    o_dtype=cutlass.BFloat16, acc_dtype=cutlass.Float32, epilogue_dtype=cutlass.Float32,
+    use_2cta_instrs=False,
+)
+print(f'n={n}: Compiling reference FMHA...', flush=True)
+try:
+    kernel.run(q, k, v, c, stream)
+    torch.cuda.synchronize()
+    out = c[0,0].float()
+    cos = torch.nn.functional.cosine_similarity(out.flatten().unsqueeze(0), ref.flatten().unsqueeze(0)).item()
+    print(f'Reference FMHA n={n} (2 tiles): cos {cos:.6f}  {"PASS" if cos >= 0.99 else "FAIL"}')
+    if cos < 0.99:
+        print(f'  out[0,:4]={out[0,:4].tolist()}')
+        print(f'  ref[0,:4]={ref[0,:4].tolist()}')
+except Exception as e:
+    import traceback; traceback.print_exc()