From 85cc95fa59f24a9a8324c015e740b76e7d507290 Mon Sep 17 00:00:00 2001
From: Li Wei <liwei.109@outlook.com>
Date: Wed, 11 Mar 2026 13:02:12 +0800
Subject: [PATCH] [dev] split fused moe experts to ensure quantization

Signed-off-by: Li Wei <liwei.109@outlook.com>
---
 examples/model_free_ptq/qwen3.5_int8.py       | 24 ++++++++
 .../entrypoints/model_free/process.py         | 61 +++++++++++++++++++
 2 files changed, 85 insertions(+)
 create mode 100644 examples/model_free_ptq/qwen3.5_int8.py

diff --git a/examples/model_free_ptq/qwen3.5_int8.py b/examples/model_free_ptq/qwen3.5_int8.py
new file mode 100644
index 0000000000..29703b7a64
--- /dev/null
+++ b/examples/model_free_ptq/qwen3.5_int8.py
@@ -0,0 +1,24 @@
+from llmcompressor import model_free_ptq
+
+MODEL_ID = "Qwen/Qwen3.5-35B-A3B"
+SAVE_DIR = MODEL_ID.rstrip("/").split("/")[-1] + "-W8A8-INT8"
+
+# Apply W8A8 to the model
+# Once quantized, the model is saved
+# using compressed-tensors to the SAVE_DIR.
+model_free_ptq(
+    model_stub=MODEL_ID,
+    save_directory=SAVE_DIR,
+    scheme="W8A8",
+    ignore=[
+        "lm_head",
+        "re:.*mlp.gate$",
+        "re:.*mlp.shared_expert_gate.*",
+        "re:.*norm.*",
+        "re:.*embed_tokens.*",
+        "re:.*visual.*",
+        "re:.*conv1d.*"
+    ],
+    max_workers=15,
+    device="cuda:0",
+)
diff --git a/src/llmcompressor/entrypoints/model_free/process.py b/src/llmcompressor/entrypoints/model_free/process.py
index 44835c7f81..a6c4e3709b 100644
--- a/src/llmcompressor/entrypoints/model_free/process.py
+++ b/src/llmcompressor/entrypoints/model_free/process.py
@@ -77,6 +77,7 @@ def process_file(
     """
     assert not is_microscale_scheme(scheme), "Use `_process_file_microscale_scheme`"
     tensors = load_file(file_path)
+    tensors = split_fused_moe_experts(tensors)
 
     if converter is not None:
         converter.process(tensors)
@@ -194,3 +195,63 @@ def process_file_microscale_scheme(
     total_size = sum(tensor.nbytes for tensor in tensors.values())
     weight_map = {key: os.path.basename(save_path) for key in tensors.keys()}
     return total_size, weight_map
+
+
+def split_fused_moe_experts(tensors: dict[str, torch.Tensor]) -> dict[str, torch.Tensor]:
+    """
+    Find fused MoE experts (with gate_up_proj/down_proj).
+    Split them from 3D tensors into individual 2D expert tensors.
+    
+    Args:
+        tensors: Dictionary of loaded tensors from safetensors file
+        
+    Returns:
+        New dictionary with split expert weights
+    """
+    _tensors = {}
+    
+    for name, tensor in tensors.items():
+        # Check if this is a MoE expert weight (3D tensor for experts)
+        if tensor.ndim == 3 and ("experts.gate_up_proj" in name or "experts.down_proj" in name):
+            # Get number of experts
+            num_experts = tensor.shape[0]
+            
+            if "gate_up_proj" in name:
+                # gate_up_proj is typically [num_experts, 2*intermediate, hidden]
+                if tensor.shape[1] % 2 != 0:
+                    print(f"Warning: gate_up_proj {name} has odd second dimension: {tensor.shape}")
+                    continue
+                    
+                hidden_size = tensor.shape[1] // 2
+                
+                # Split into individual experts
+                for expert_idx in range(num_experts):
+                    expert_tensor = tensor[expert_idx]  # [2*hidden, intermediate]
+                    
+                    # Split gate and up projections
+                    gate_proj = expert_tensor[:hidden_size, :]
+                    up_proj = expert_tensor[hidden_size:, :]
+                    
+                    # Create new key names
+                    base_key = name.replace("mlp.experts.gate_up_proj", f"mlp.experts.{expert_idx}")
+                    _tensors[base_key + ".gate_proj.weight"] = gate_proj
+                    _tensors[base_key + ".up_proj.weight"] = up_proj
+                    
+                print(f"Split {name} into {num_experts} experts")
+                
+            elif "down_proj" in name:
+                # down_proj is typically [num_experts, hidden, intermediate]
+                # Split into individual experts
+                for expert_idx in range(num_experts):
+                    down_proj = tensor[expert_idx]  # [hidden, intermediate]
+                    
+                    # Create new key name
+                    new_key = name.replace("mlp.experts.down_proj", f"mlp.experts.{expert_idx}") + ".down_proj.weight"
+                    _tensors[new_key] = down_proj
+                    
+                print(f"Split {name} into {num_experts} experts")
+        else:
+            # Non-MoE or non-3D tensors, keep as is
+            _tensors[name] = tensor
+    
+    return _tensors
\ No newline at end of file