diff --git a/litellm/litellm_core_utils/exception_mapping_utils.py b/litellm/litellm_core_utils/exception_mapping_utils.py
index cfe1e420b3b..bf2ab6a5804 100644
--- a/litellm/litellm_core_utils/exception_mapping_utils.py
+++ b/litellm/litellm_core_utils/exception_mapping_utils.py
@@ -2225,15 +2225,17 @@ def _map_openrouter_exception(
             )
         elif original_exception.status_code == 404:
             if "supporting your data region" in error_str.lower():
-                response_obj = getattr(original_exception, "response", None)
-                inferred_region = None
-                if response_obj is not None and getattr(response_obj, "url", None):
-                    from litellm.llms.openrouter.data_residency import infer_openrouter_data_residency
+                response_obj: Final = getattr(original_exception, "response", None)
+                from litellm.llms.openrouter.data_residency import infer_openrouter_data_residency
 
-                    inferred_region = infer_openrouter_data_residency(
+                inferred_region: Final[str | None] = (
+                    infer_openrouter_data_residency(
                         custom_llm_provider="openrouter",
                         api_base=str(response_obj.url),
                     )
+                    if response_obj is not None and getattr(response_obj, "url", None)
+                    else None
+                )
                 raise OpenRouterRegionNotSupportedError(
                     message=f"OpenRouterRegionNotSupportedError: {exception_provider} - {error_str}",
                     model=model,
diff --git a/litellm/llms/openrouter/chat/transformation.py b/litellm/llms/openrouter/chat/transformation.py
index 61d527b6e48..daf4ca253eb 100644
--- a/litellm/llms/openrouter/chat/transformation.py
+++ b/litellm/llms/openrouter/chat/transformation.py
@@ -52,31 +52,29 @@ class OpenrouterConfig(OpenAIGPTConfig):
     def __init__(
         self,
         region: str | None = None,
-        **kwargs: object,
     ) -> None:
         self.region = region
-        super().__init__(**kwargs)
+        super().__init__()
 
     def get_complete_url(
         self,
         api_base: str | None,
         api_key: str | None,
         model: str,
-        optional_params: dict,
-        litellm_params: dict,
+        optional_params: Mapping[str, object] | None = None,
+        litellm_params: Mapping[str, object] | None = None,
         stream: bool | None = None,
     ) -> str:
-        api_base = resolve_openrouter_api_base(
+        resolved_base: Final = resolve_openrouter_api_base(
             api_base=api_base,
             region=self.region,
             litellm_params=litellm_params,
             optional_params=optional_params,
-        )
+        ).rstrip("/")
         endpoint: Final = "chat/completions"
-        api_base = api_base.rstrip("/")
-        if endpoint in api_base:
-            return api_base
-        return f"{api_base}/{endpoint}"
+        if endpoint in resolved_base:
+            return resolved_base
+        return f"{resolved_base}/{endpoint}"
 
     def get_supported_openai_params(self, model: str) -> list:
         """
diff --git a/litellm/llms/openrouter/data_residency.py b/litellm/llms/openrouter/data_residency.py
index 9d31c3c0483..6c38254bd60 100644
--- a/litellm/llms/openrouter/data_residency.py
+++ b/litellm/llms/openrouter/data_residency.py
@@ -9,6 +9,8 @@ OpenRouter provides dedicated regional endpoints for end-to-end data residency:
 Docs: https://openrouter.ai/docs/guides/features/in-region-routing
 """
 
+from collections.abc import Mapping, MutableMapping
+from types import MappingProxyType
 from typing import Final
 from urllib.parse import urlparse
 
@@ -16,19 +18,23 @@ import litellm
 from litellm.secret_managers.main import get_secret_str
 
 # Normalized region names mapped to their dedicated OpenRouter base URLs
-_OPENROUTER_REGIONAL_URLS: Final[dict[str, str]] = {
-    "eu": "https://eu.openrouter.ai/api/v1",
-    "europe": "https://eu.openrouter.ai/api/v1",
-    "us": "https://us.openrouter.ai/api/v1",
-    "usa": "https://us.openrouter.ai/api/v1",
-    "united states": "https://us.openrouter.ai/api/v1",
-}
+_OPENROUTER_REGIONAL_URLS: Final[Mapping[str, str]] = MappingProxyType(
+    {
+        "eu": "https://eu.openrouter.ai/api/v1",
+        "europe": "https://eu.openrouter.ai/api/v1",
+        "us": "https://us.openrouter.ai/api/v1",
+        "usa": "https://us.openrouter.ai/api/v1",
+        "united states": "https://us.openrouter.ai/api/v1",
+    }
+)
 
 # OpenRouter regional hostnames mapped to canonical data residency codes ("eu", "us")
-_OPENROUTER_REGIONAL_HOSTNAMES: Final[dict[str, str]] = {
-    "eu.openrouter.ai": "eu",
-    "us.openrouter.ai": "us",
-}
+_OPENROUTER_REGIONAL_HOSTNAMES: Final[Mapping[str, str]] = MappingProxyType(
+    {
+        "eu.openrouter.ai": "eu",
+        "us.openrouter.ai": "us",
+    }
+)
 
 _DEFAULT_OPENROUTER_API_BASE: Final[str] = "https://openrouter.ai/api/v1"
 
@@ -36,8 +42,8 @@ _DEFAULT_OPENROUTER_API_BASE: Final[str] = "https://openrouter.ai/api/v1"
 def resolve_openrouter_api_base(
     api_base: str | None = None,
     region: str | None = None,
-    litellm_params: dict | None = None,
-    optional_params: dict | None = None,
+    litellm_params: Mapping[str, object] | None = None,
+    optional_params: Mapping[str, object] | None = None,
 ) -> str:
     """
     Resolve the OpenRouter API base URL based on custom api_base, explicit region, or environment.
@@ -48,34 +54,44 @@ def resolve_openrouter_api_base(
     3. Fallback to `api_base or litellm.api_base or OPENROUTER_API_BASE or default global URL`.
     """
     # Check if a custom api_base was provided that is not the default global endpoint
-    is_custom_api_base = False
-    if api_base:
-        cleaned_base = api_base.rstrip("/").lower()
-        if cleaned_base not in ("https://openrouter.ai/api/v1", "https://openrouter.ai", "http://openrouter.ai"):
-            is_custom_api_base = True
+    cleaned_base: Final[str | None] = api_base.rstrip("/").lower() if api_base else None
+    is_custom_api_base: Final[bool] = bool(
+        cleaned_base
+        and cleaned_base not in ("https://openrouter.ai/api/v1", "https://openrouter.ai", "http://openrouter.ai")
+    )
 
     if is_custom_api_base and api_base:
         return api_base
 
     # Check for region in litellm_params, optional_params, explicit region argument, config, or environment
-    resolved_region = None
-    if isinstance(litellm_params, dict):
-        resolved_region = (
-            litellm_params.get("region") or litellm_params.get("region_name") or litellm_params.get("data_residency")
-        )
-    if not resolved_region and isinstance(optional_params, dict):
-        resolved_region = (
+    raw_from_params: Final[object] = (
+        litellm_params.get("region") or litellm_params.get("region_name") or litellm_params.get("data_residency")
+        if isinstance(litellm_params, Mapping)
+        else None
+    )
+    raw_from_optional: Final[object] = (
+        (
             optional_params.pop("region", None)
             or optional_params.pop("region_name", None)
             or optional_params.pop("data_residency", None)
         )
-    if not resolved_region:
-        resolved_region = (
-            region or getattr(litellm, "openrouter_region", None) or getattr(litellm, "openrouter_data_residency", None)
+        if isinstance(optional_params, MutableMapping)
+        else (
+            optional_params.get("region") or optional_params.get("region_name") or optional_params.get("data_residency")
+            if isinstance(optional_params, Mapping)
+            else None
         )
+    )
+    resolved_region: Final[object] = (
+        raw_from_params
+        or raw_from_optional
+        or region
+        or getattr(litellm, "openrouter_region", None)
+        or getattr(litellm, "openrouter_data_residency", None)
+    )
 
     if resolved_region and isinstance(resolved_region, str):
-        normalized_region = resolved_region.strip().lower()
+        normalized_region: Final[str] = resolved_region.strip().lower()
         if normalized_region in ("global", "default"):
             return _DEFAULT_OPENROUTER_API_BASE
         if normalized_region in _OPENROUTER_REGIONAL_URLS:
diff --git a/litellm/llms/openrouter/embedding/transformation.py b/litellm/llms/openrouter/embedding/transformation.py
index eb022a81228..54c8e8a20c9 100644
--- a/litellm/llms/openrouter/embedding/transformation.py
+++ b/litellm/llms/openrouter/embedding/transformation.py
@@ -85,15 +85,14 @@ class OpenrouterEmbeddingConfig(BaseEmbeddingConfig):
         """
         Get the complete URL for OpenRouter Embedding API endpoint.
         """
-        api_base = resolve_openrouter_api_base(
+        resolved_base: Final = resolve_openrouter_api_base(
             api_base=api_base,
             litellm_params=litellm_params,
             optional_params=optional_params,
-        )
-        api_base = api_base.rstrip("/")
+        ).rstrip("/")
 
         # Return the embeddings endpoint
-        return f"{api_base}/embeddings"
+        return f"{resolved_base}/embeddings"
 
     def transform_embedding_request(
         self,
diff --git a/litellm/main.py b/litellm/main.py
index 14187c18ba2..2e92dd5a325 100644
--- a/litellm/main.py
+++ b/litellm/main.py
@@ -3415,7 +3415,7 @@ def _complete_openrouter(ctx: CompletionDispatchContext) -> _CompletionDispatchR
 
     ## Load Config
     config: Final = litellm.OpenrouterConfig.get_config()
-    api_base = resolve_openrouter_api_base(
+    api_base = resolve_openrouter_api_base(  # rebind-ok: regional endpoint resolution for openrouter
         api_base=api_base,
         region=getattr(config, "region", None),
         litellm_params=litellm_params,
@@ -6788,7 +6788,7 @@ def embedding(
                 headers=headers,
             )
         elif custom_llm_provider == "openrouter":
-            api_base = resolve_openrouter_api_base(
+            api_base = resolve_openrouter_api_base(  # rebind-ok: regional endpoint resolution for openrouter
                 api_base=api_base,
                 litellm_params=litellm_params_dict,
                 optional_params=optional_params,