diff --git a/tests/test_llm_routing.py b/tests/test_llm_routing.py
index c4841684..a0d631d2 100644
--- a/tests/test_llm_routing.py
+++ b/tests/test_llm_routing.py
@@ -300,6 +300,18 @@ def test_google_client_passes_base_url_to_langchain(monkeypatch):
     assert captured_kwargs["base_url"] == "https://google.example/v1beta"
 
 
+def test_default_config_copy_does_not_share_mutable_llm_routing_state():
+    config = default_config.DEFAULT_CONFIG.copy()
+
+    assert config["llm_routing"] is None
+    config["llm_routing"] = {
+        "default": {},
+        "roles": {"portfolio_manager": {"model": "gpt-5.2"}},
+    }
+
+    assert default_config.DEFAULT_CONFIG["llm_routing"] is None
+
+
 def test_dataflow_config_returns_isolated_nested_routing(monkeypatch):
     monkeypatch.setattr(dataflow_config, "_config", None)
     dataflow_config.initialize_config()
@@ -311,7 +323,7 @@ def test_dataflow_config_returns_isolated_nested_routing(monkeypatch):
     }
 
     assert dataflow_config.get_config()["llm_routing"]["roles"] == {}
-    assert default_config.DEFAULT_CONFIG["llm_routing"]["roles"] == {}
+    assert default_config.DEFAULT_CONFIG["llm_routing"] is None
 
 
 def test_log_state_writes_json_snapshot(tmp_path, monkeypatch):
diff --git a/tradingagents/dataflows/config.py b/tradingagents/dataflows/config.py
index 2714eb61..9b398de1 100644
--- a/tradingagents/dataflows/config.py
+++ b/tradingagents/dataflows/config.py
@@ -20,20 +20,22 @@ def initialize_config():
     """Initialize the configuration with default values."""
     global _config
     if _config is None:
-        _config = deepcopy(default_config.DEFAULT_CONFIG)
+        _config = default_config.normalize_llm_routing(default_config.DEFAULT_CONFIG)
 
 
 def set_config(config: Dict):
     """Update the configuration with custom values."""
     global _config
-    _config = _deep_merge_dicts(default_config.DEFAULT_CONFIG, config)
+    _config = default_config.normalize_llm_routing(
+        _deep_merge_dicts(default_config.DEFAULT_CONFIG, config)
+    )
 
 
 def get_config() -> Dict:
     """Get the current configuration."""
     if _config is None:
         initialize_config()
-    return deepcopy(_config)
+    return default_config.normalize_llm_routing(_config)
 
 
 # Initialize with default config
diff --git a/tradingagents/default_config.py b/tradingagents/default_config.py
index 2a3e7f2e..cf3bdc96 100644
--- a/tradingagents/default_config.py
+++ b/tradingagents/default_config.py
@@ -1,5 +1,24 @@
+from copy import deepcopy
 import os
 
+
+def normalize_llm_routing(config):
+    """Return config with llm_routing normalized to the expected dict shape."""
+    normalized = deepcopy(config)
+    llm_routing = normalized.get("llm_routing")
+
+    if not isinstance(llm_routing, dict):
+        normalized["llm_routing"] = {"default": {}, "roles": {}}
+        return normalized
+
+    default_route = llm_routing.get("default")
+    role_routes = llm_routing.get("roles")
+    normalized["llm_routing"] = {
+        "default": deepcopy(default_route) if isinstance(default_route, dict) else {},
+        "roles": deepcopy(role_routes) if isinstance(role_routes, dict) else {},
+    }
+    return normalized
+
 DEFAULT_CONFIG = {
     "project_dir": os.path.abspath(os.path.join(os.path.dirname(__file__), ".")),
     "results_dir": os.getenv("TRADINGAGENTS_RESULTS_DIR", "./results"),
@@ -12,10 +31,7 @@ DEFAULT_CONFIG = {
     "deep_think_llm": "gpt-5.2",
     "quick_think_llm": "gpt-5-mini",
     "backend_url": "https://api.openai.com/v1",
-    "llm_routing": {
-        "default": {},
-        "roles": {},
-    },
+    "llm_routing": None,
     # Provider-specific thinking configuration
     "google_thinking_level": None,      # "high", "minimal", etc.
     "openai_reasoning_effort": None,    # "medium", "high", "low"
diff --git a/tradingagents/graph/trading_graph.py b/tradingagents/graph/trading_graph.py
index bec32a33..f453d782 100644
--- a/tradingagents/graph/trading_graph.py
+++ b/tradingagents/graph/trading_graph.py
@@ -11,7 +11,7 @@ from langgraph.prebuilt import ToolNode
 from tradingagents.llm_clients import create_llm_client
 
 from tradingagents.agents import *
-from tradingagents.default_config import DEFAULT_CONFIG
+from tradingagents.default_config import DEFAULT_CONFIG, normalize_llm_routing
 from tradingagents.agents.utils.memory import FinancialSituationMemory
 from tradingagents.agents.utils.agent_states import (
     AgentState,
@@ -144,7 +144,7 @@ class TradingAgentsGraph:
 
     def _build_config(self, config: Optional[Dict[str, Any]]) -> Dict[str, Any]:
         """Merge user config over defaults without mutating the shared defaults."""
-        return self._deep_merge_dicts(DEFAULT_CONFIG, config or {})
+        return normalize_llm_routing(self._deep_merge_dicts(DEFAULT_CONFIG, config or {}))
 
     def _normalize_provider(self, provider: Optional[str]) -> str:
         return (provider or "").lower()