diff --git a/examples/gemma4/ort_genai/vlm/genai_config.json b/examples/gemma4/ort_genai/vlm/genai_config.json
index c47657bf..c53e3a5f 100644
--- a/examples/gemma4/ort_genai/vlm/genai_config.json
+++ b/examples/gemma4/ort_genai/vlm/genai_config.json
@@ -4,7 +4,10 @@
         "vocab_size": 262144,
         "context_length": 131072,
         "bos_token_id": 2,
-        "eos_token_id": [1, 106],
+        "eos_token_id": [
+            1,
+            106
+        ],
         "pad_token_id": 0,
         "image_token_id": 255999,
         "decoder": {
@@ -12,7 +15,7 @@
                 "log_id": "onnxruntime-genai",
                 "provider_options": []
             },
-            "filename": "model.onnx",
+            "filename": "decoder/model.onnx",
             "hidden_size": 1536,
             "head_size": 256,
             "num_attention_heads": 8,
@@ -37,12 +40,26 @@
                 "alignment": "right",
                 "slide_key_value_cache": true,
                 "slide_inputs": true,
-                "layers": [0, 1, 2, 3, 5, 6, 7, 8, 10, 11, 12, 13]
+                "layers": [
+                    0,
+                    1,
+                    2,
+                    3,
+                    5,
+                    6,
+                    7,
+                    8,
+                    10,
+                    11,
+                    12,
+                    13
+                ]
             }
         },
         "vision": {
             "filename": "vision.onnx",
             "config_filename": "processor_config.json",
+            "spatial_merge_size": 2,
             "session_options": {
                 "log_id": "onnxruntime-genai",
                 "provider_options": []
diff --git a/src/mobius/integrations/ort_genai/auto_export.py b/src/mobius/integrations/ort_genai/auto_export.py
index fe2afe28..37a9ff74 100644
--- a/src/mobius/integrations/ort_genai/auto_export.py
+++ b/src/mobius/integrations/ort_genai/auto_export.py
@@ -196,7 +196,9 @@ def _write_processor_config(
             "patch_size": getattr(vision, "patch_size", None) or 14,
         }
 
-    path = os.path.join(output_dir, "processor_config.json")
+    proc_filename = "processor_config.json"
+
+    path = os.path.join(output_dir, proc_filename)
     with open(path, "w", encoding="utf-8") as f:
         json.dump(processor, f, indent=4)
     return path
@@ -275,8 +277,9 @@ def _write_genai_config(
                 vision_kwargs["spatial_merge_size"] = None
                 vision_kwargs["config_filename"] = "vision_processor.json"
             elif model_type in ("gemma4", "gemma4_text"):
-                vision_kwargs["spatial_merge_size"] = None
-                vision_kwargs["config_filename"] = "processor_config.json"
+                vision_cfg = getattr(config, "vision", None)
+                sms = getattr(vision_cfg, "spatial_merge_size", 2)
+                vision_kwargs["spatial_merge_size"] = sms
 
             if vision_input_mapping is not None:
                 vision_kwargs["input_names"] = vision_input_mapping
diff --git a/src/mobius/integrations/ort_genai/auto_export_test.py b/src/mobius/integrations/ort_genai/auto_export_test.py
index 0ab5ada7..60b8c21c 100644
--- a/src/mobius/integrations/ort_genai/auto_export_test.py
+++ b/src/mobius/integrations/ort_genai/auto_export_test.py
@@ -586,7 +586,7 @@ def test_gemma4_vision_inputs(self, tmp_path):
         assert "pixel_values" in vision_inputs
         assert "pixel_position_ids" in vision_inputs
         assert "image_grid_thw" not in vision_inputs
-        assert "spatial_merge_size" not in data["model"]["vision"]
+        assert data["model"]["vision"]["spatial_merge_size"] == 2
 
     def test_gemma4_decoder_has_input_ids_and_inputs_embeds(self, tmp_path):
         """Gemma4 decoder has both inputs_embeds and input_ids."""
@@ -779,7 +779,7 @@ def test_gemma4_genai_config_from_real_model(self, tmp_path):
 
         # Config-level properties are still present
         assert data["model"]["image_token_id"] == 255999
-        assert "spatial_merge_size" not in data["model"]["vision"]
+        assert data["model"]["vision"]["spatial_merge_size"] == 2
         assert data["model"]["vision"]["config_filename"] == "processor_config.json"
 
     def test_auto_export_produces_genai_config(self, tmp_path):
diff --git a/src/mobius/integrations/ort_genai/genai_config.py b/src/mobius/integrations/ort_genai/genai_config.py
index e35b15db..9d83e6cc 100644
--- a/src/mobius/integrations/ort_genai/genai_config.py
+++ b/src/mobius/integrations/ort_genai/genai_config.py
@@ -353,9 +353,10 @@ def generate(self) -> dict[str, Any]:
             decoder_inputs = dict(self._decoder_inputs)
         else:
             decoder_inputs = _default_decoder_inputs(is_vlm=is_multimodal)
+        decoder_filename = "decoder/model.onnx" if is_multimodal else "model.onnx"
         decoder: dict[str, Any] = {
             "session_options": _make_session_options(self.ep),
-            "filename": "model.onnx",
+            "filename": decoder_filename,
             "head_size": self.head_dim,
             "hidden_size": self.hidden_size,
             "inputs": decoder_inputs,