diff --git a/aidefense/config.py b/aidefense/config.py
index 79402ef..d2e58ce 100644
--- a/aidefense/config.py
+++ b/aidefense/config.py
@@ -83,6 +83,8 @@ def __new__(cls, *args, **kwargs):
 
         return cls._instances[cls]
 
+    _logger = logging.getLogger("aidefense_sdk.config")
+
     def __init__(self, *args, **kwargs):
         # Double-checked locking: fast path avoids the lock for already-init'd
         # singletons; the lock prevents concurrent first-time callers from both
@@ -96,6 +98,8 @@ def __init__(self, *args, **kwargs):
                     except Exception:
                         self._instances.pop(type(self), None)
                         raise
+        elif args or kwargs:
+            self._warn_if_params_differ(*args, **kwargs)
 
     def _set_region(self, region: str):
         if not isinstance(region, str):
@@ -178,6 +182,53 @@ def _set_pool_config(self, pool_config: dict):
             "pool_maxsize": pool_config.get("pool_maxsize", self.DEFAULT_POOL_MAXSIZE),
         }
 
+    _INIT_PARAM_NAMES = (
+        "region", "runtime_base_url", "management_base_url", "timeout",
+    )
+
+    def _warn_if_params_differ(self, *args, **kwargs):
+        """Log a warning when the singleton is re-requested with different parameters."""
+        merged = dict(zip(self._INIT_PARAM_NAMES, args))
+        merged.update(kwargs)
+
+        _NORMALIZERS = {
+            "region": self._normalize_requested_region,
+            "runtime_base_url": self._normalize_url,
+            "management_base_url": self._normalize_url,
+        }
+        diffs = []
+        for key in self._INIT_PARAM_NAMES:
+            if key not in merged or merged[key] is None:
+                continue
+            requested = merged[key]
+            normalizer = _NORMALIZERS.get(key)
+            if normalizer:
+                requested = normalizer(requested)
+            current = getattr(self, key, None)
+            if current is not None and requested != current:
+                diffs.append(f"{key}={current!r} (requested {merged[key]!r})")
+        if diffs:
+            self._logger.warning(
+                "%s singleton already initialized. Ignoring different "
+                "parameters: %s. Construct %s once and share it, or clear "
+                "%s._instances to re-initialize.",
+                type(self).__name__,
+                ", ".join(diffs),
+                type(self).__name__,
+                type(self).__name__,
+            )
+
+    @staticmethod
+    def _normalize_requested_region(region):
+        """Map short-code regions to canonical names for comparison."""
+        _SHORT = {"us": "us-west-2", "eu": "eu-central-1", "apj": "ap-northeast-1"}
+        return _SHORT.get(region, region) if isinstance(region, str) else region
+
+    @staticmethod
+    def _normalize_url(url):
+        """Strip trailing slash to match stored value normalization."""
+        return url.rstrip("/") if isinstance(url, str) else url
+
     @abstractmethod
     def _initialize(self, *args, **kwargs):
         pass
diff --git a/aidefense/tests/test_config.py b/aidefense/tests/test_config.py
index 4618f41..5b51d80 100644
--- a/aidefense/tests/test_config.py
+++ b/aidefense/tests/test_config.py
@@ -75,3 +75,59 @@ def test_config_with_pool_config():
     config = Config(pool_config=pool_conf)
     assert config.connection_pool._pool_connections == 3
     assert config.connection_pool._pool_maxsize == 7
+
+
+def test_config_warns_on_different_region(caplog):
+    Config(region="us-west-2")
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config(region="eu-central-1")
+    assert "already initialized" in caplog.text
+    assert "region" in caplog.text
+    assert "eu-central-1" in caplog.text
+
+
+def test_config_warns_on_different_timeout(caplog):
+    Config(timeout=30)
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config(timeout=60)
+    assert "already initialized" in caplog.text
+    assert "timeout" in caplog.text
+
+
+def test_config_no_warning_on_same_params(caplog):
+    Config(region="us-west-2", timeout=30)
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config(region="us-west-2", timeout=30)
+    assert "already initialized" not in caplog.text
+
+
+def test_config_no_warning_on_short_region_alias(caplog):
+    """'us' normalizes to 'us-west-2', so no mismatch warning."""
+    Config(region="us-west-2")
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config(region="us")
+    assert "already initialized" not in caplog.text
+
+
+def test_config_no_warning_when_no_kwargs(caplog):
+    Config(region="eu-central-1")
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config()
+    assert "already initialized" not in caplog.text
+
+
+def test_config_warns_on_positional_region_mismatch(caplog):
+    """Positional args (not just kwargs) must trigger the warning."""
+    Config("us-west-2")
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config("eu-central-1")
+    assert "already initialized" in caplog.text
+    assert "region" in caplog.text
+
+
+def test_config_no_false_positive_on_trailing_slash_url(caplog):
+    """URLs with trailing slashes should be normalized before comparison."""
+    Config(runtime_base_url="https://custom.endpoint.com/")
+    with caplog.at_level(logging.WARNING, logger="aidefense_sdk.config"):
+        Config(runtime_base_url="https://custom.endpoint.com/")
+    assert "already initialized" not in caplog.text