diff --git a/src/agora_agent/agentkit/vendors/mllm.py b/src/agora_agent/agentkit/vendors/mllm.py
index f973a30..4a0846a 100644
--- a/src/agora_agent/agentkit/vendors/mllm.py
+++ b/src/agora_agent/agentkit/vendors/mllm.py
@@ -164,6 +164,9 @@ def to_config(self) -> Dict[str, Any]:
         # matching the TypeScript SDK.
         params: Dict[str, Any] = dict(self.options.additional_params or {})
         params["model"] = self.options.model
+        params["project_id"] = self.options.project_id
+        params["location"] = self.options.location
+        params["adc_credentials_string"] = self.options.adc_credentials_string
         if self.options.instructions is not None:
             params["instructions"] = self.options.instructions
         if self.options.voice is not None:
@@ -182,9 +185,6 @@ def to_config(self) -> Dict[str, Any]:
         config: Dict[str, Any] = {
             "vendor": "vertexai",
             "url": self.options.url if self.options.url is not None else "",
-            "project_id": self.options.project_id,
-            "location": self.options.location,
-            "adc_credentials_string": self.options.adc_credentials_string,
             "params": params,
         }
         if self.options.greeting_message is not None:
diff --git a/tests/custom/test_agentkit_vendors.py b/tests/custom/test_agentkit_vendors.py
index 031acfb..888c87a 100644
--- a/tests/custom/test_agentkit_vendors.py
+++ b/tests/custom/test_agentkit_vendors.py
@@ -110,12 +110,13 @@ def test_vertex_ai_explicit_fields_override_additional_params():
     ).to_config()
 
     assert config["vendor"] == "vertexai"
-    # routing fields are top-level, not inside params
-    assert config["project_id"] == "explicit-project"
-    assert config["location"] == "explicit-region"
-    assert config["adc_credentials_string"] == "{}"
-    # model and extra_key live inside params
+    assert "project_id" not in config
+    assert "location" not in config
+    assert "adc_credentials_string" not in config
     assert config["params"]["model"] == "explicit-model"
+    assert config["params"]["project_id"] == "explicit-project"
+    assert config["params"]["location"] == "explicit-region"
+    assert config["params"]["adc_credentials_string"] == "{}"
     assert config["params"]["extra_key"] == "kept"
 
 
diff --git a/tests/custom/test_request_body.py b/tests/custom/test_request_body.py
index 7e6d09a..5149244 100644
--- a/tests/custom/test_request_body.py
+++ b/tests/custom/test_request_body.py
@@ -1272,10 +1272,10 @@ def test_byok_vertex_ai_mllm_params() -> None:
     props = build_properties(agent)
     assert props["mllm"]["vendor"] == "vertexai"
     assert props["mllm"]["url"] == ""
-    assert props["mllm"]["project_id"] == "my-project"
-    assert props["mllm"]["location"] == "us-central1"
-    assert props["mllm"]["adc_credentials_string"] == "{}"
     assert props["mllm"]["params"]["model"] == "gemini-live-2.5-flash"
+    assert props["mllm"]["params"]["project_id"] == "my-project"
+    assert props["mllm"]["params"]["location"] == "us-central1"
+    assert props["mllm"]["params"]["adc_credentials_string"] == "{}"
 
 
 def test_byok_xai_grok_mllm_params() -> None: