diff --git a/docs/my-website/docs/proxy/pass_through.md b/docs/my-website/docs/proxy/pass_through.md
index e9c1d796969..f47d7064140 100644
--- a/docs/my-website/docs/proxy/pass_through.md
+++ b/docs/my-website/docs/proxy/pass_through.md
@@ -58,6 +58,17 @@ Configure the required authentication and pricing:
 - The Bria API requires an `api_token` header
 - Enter your Bria API key as the value for the `api_token` header
 
+**Default Query Parameters (Optional):**
+- Add query parameters that will be automatically sent with every request
+- Perfect for API versioning, format specifications, or default configurations
+- Clients can override these parameters by providing their own values
+- Example: `version=v1`, `format=json`, `timeout=30`
+
+<Image 
+  img={require('../../img/passthrough_query_default.png')}
+  style={{width: '60%', display: 'block', margin: '2rem auto'}}
+/>
+
 **Pricing Configuration:**
 - Set a cost per request (e.g., $12.00 in this example)
 - This enables cost tracking and billing for your users
@@ -112,6 +123,9 @@ general_settings:
         content-type: application/json
         accept: application/json
       forward_headers: true                               # Forward all incoming headers
+      default_query_params:                               # Optional: Default query parameters
+        version: "v1"                                     # Always send version=v1
+        format: "json"                                    # Default format (can be overridden)
 ```
 
 ### Start and Test
@@ -167,6 +181,8 @@ general_settings:
       forward_headers: boolean        # Forward all incoming headers
       include_subpath: boolean        # If true, forwards requests to sub-paths (default: false)
       methods: list[string]           # Optional: HTTP methods (e.g., ["GET", "POST"]). If not specified, all methods are supported.
+      default_query_params:           # Optional: Default query parameters sent with every request
+        <param-name>: string          # Key-value pairs (e.g., version: "v1", format: "json")
       headers:                        # Custom headers to add
         Authorization: string         # Auth header for target API
         content-type: string         # Request content type
@@ -178,11 +194,17 @@ general_settings:
 
 ### Header Options
 - **Authorization**: Authentication for the target API
-- **content-type**: Request body format specification  
+- **content-type**: Request body format specification
 - **accept**: Expected response format
 - **LANGFUSE_PUBLIC_KEY/SECRET_KEY**: For Langfuse integration
 - **Custom headers**: Any additional key-value pairs
 
+### Default Query Parameters
+- **Parameter precedence**: Client params > URL params > default params
+- **Use cases**: API versioning, authentication tokens, format control, feature flags
+- **Override capability**: Clients can override any default parameter
+- **Examples**: `version: "v1"`, `format: "json"`, `timeout: "30"`
+
 ### Sub-path Routing
 
 By default, pass-through endpoints only match the **exact path** specified. To forward requests to sub-paths, set `include_subpath: true`:
@@ -202,7 +224,51 @@ general_settings:
 
 ---
 
-### Method-Specific Routing
+### Default Query Parameters
+
+Pass-through endpoints support default query parameters that are automatically added to every request. This is useful for API versioning, format specifications, authentication tokens, or any default configuration.
+
+#### How It Works
+
+**Parameter Precedence (highest to lowest priority):**
+1. **Client-provided parameters** (in the request URL)
+2. **URL parameters** (from the target URL)
+3. **Default parameters** (from configuration)
+
+#### Example Configuration
+
+```yaml
+general_settings:
+  pass_through_endpoints:
+    - path: "/api/v1"
+      target: "https://external-api.com/service?timeout=60"  # URL has timeout=60
+      default_query_params:
+        version: "v1"          # Always add version=v1
+        format: "json"         # Default format=json (can be overridden)
+        auth_level: "basic"    # Always add auth_level=basic
+```
+
+#### Request Examples
+
+**Client Request:** `GET /api/v1/users`
+**Actual Backend Call:** `https://external-api.com/service?version=v1&format=json&auth_level=basic&timeout=60`
+
+**Client Request:** `GET /api/v1/users?format=xml&custom=value`
+**Actual Backend Call:** `https://external-api.com/service?version=v1&auth_level=basic&timeout=60&format=xml&custom=value`
+- Client `format=xml` overrides default `format=json`
+- Default `version=v1` and `auth_level=basic` are preserved
+- URL `timeout=60` is preserved
+- Client `custom=value` is added
+
+#### Use Cases
+
+- **API Versioning**: Always send `version=v2` to maintain compatibility
+- **Authentication**: Add authentication tokens like `api_key=default_key`
+- **Format Control**: Default to `format=json` but allow client override
+- **Rate Limiting**: Set `rate_limit=standard` as default
+- **Feature Flags**: Enable `experimental=false` by default
+
+---
 
 You can configure different target URLs for the same path using different HTTP methods. This is useful when different backends handle different operations:
 
diff --git a/docs/my-website/img/passthrough_query_default.png b/docs/my-website/img/passthrough_query_default.png
new file mode 100644
index 00000000000..fb97e69001e
Binary files /dev/null and b/docs/my-website/img/passthrough_query_default.png differ
diff --git a/litellm/passthrough/utils.py b/litellm/passthrough/utils.py
index fbbf9cd2581..74af02e5e62 100644
--- a/litellm/passthrough/utils.py
+++ b/litellm/passthrough/utils.py
@@ -9,7 +9,9 @@ from litellm.constants import PASS_THROUGH_HEADER_PREFIX
 class BasePassthroughUtils:
     @staticmethod
     def get_merged_query_parameters(
-        existing_url: httpx.URL, request_query_params: Dict[str, Union[str, list]]
+        existing_url: httpx.URL,
+        request_query_params: Dict[str, Union[str, list]],
+        default_query_params: Optional[Dict[str, Union[str, list]]] = None
     ) -> Dict[str, Union[str, List[str]]]:
         # Get the existing query params from the target URL
         existing_query_string = existing_url.query.decode("utf-8")
@@ -19,8 +21,19 @@ class BasePassthroughUtils:
         updated_existing_query_params = {
             k: v[0] if len(v) == 1 else v for k, v in existing_query_params.items()
         }
-        # Merge the query params, giving priority to the existing ones
-        return {**request_query_params, **updated_existing_query_params}
+
+        # Start with default query params (lowest priority)
+        merged_params = {}
+        if default_query_params:
+            merged_params.update(default_query_params)
+
+        # Override with existing URL query params (medium priority)
+        merged_params.update(updated_existing_query_params)
+
+        # Override with request query params (highest priority - client can override anything)
+        merged_params.update(request_query_params)
+
+        return merged_params
 
     @staticmethod
     def forward_headers_from_request(
diff --git a/litellm/proxy/_types.py b/litellm/proxy/_types.py
index e94e41992d7..2a4fb89fd08 100644
--- a/litellm/proxy/_types.py
+++ b/litellm/proxy/_types.py
@@ -1909,6 +1909,10 @@ class PassThroughGenericEndpoint(LiteLLMPydanticObjectBase):
         default={},
         description="Key-value pairs of headers to be forwarded with the request. You can set any key value pair here and it will be forwarded to your target endpoint",
     )
+    default_query_params: dict = Field(
+        default={},
+        description="Key-value pairs of default query parameters to be sent with every request to this endpoint. These can be overridden by client-provided query parameters. For example: {'key': 'default_value', 'api_version': '2023-01'}",
+    )
     include_subpath: bool = Field(
         default=False,
         description="If True, requests to subpaths of the path will be forwarded to the target endpoint. For example, if the path is /bria and include_subpath is True, requests to /bria/v1/text-to-image/base/2.3 will be forwarded to the target endpoint.",
diff --git a/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py b/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py
index 20a446bd29b..76308e08187 100644
--- a/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py
+++ b/litellm/proxy/pass_through_endpoints/pass_through_endpoints.py
@@ -600,6 +600,7 @@ async def pass_through_request(  # noqa: PLR0915
     forward_headers: Optional[bool] = False,
     merge_query_params: Optional[bool] = False,
     query_params: Optional[dict] = None,
+    default_query_params: Optional[dict] = None,
     stream: Optional[bool] = None,
     cost_per_request: Optional[float] = None,
     custom_llm_provider: Optional[str] = None,
@@ -617,6 +618,7 @@ async def pass_through_request(  # noqa: PLR0915
         forward_headers: Whether to forward headers
         merge_query_params: Whether to merge query params
         query_params: The query params
+        default_query_params: The default query params to be applied if not overridden by client
         stream: Whether to stream the response
         cost_per_request: Optional field - cost per request to the target endpoint
         custom_llm_provider: Optional field - custom LLM provider for the endpoint
@@ -649,13 +651,18 @@ async def pass_through_request(  # noqa: PLR0915
             forward_headers=forward_headers,
         )
 
-        if merge_query_params:
+        # Apply default query parameters if provided, regardless of merge_query_params setting
+        if default_query_params or merge_query_params:
+            # Determine what to merge based on settings
+            request_params = dict(request.query_params) if merge_query_params else {}
+
             # Create a new URL with the merged query params
             url = url.copy_with(
                 query=urlencode(
                     HttpPassThroughEndpointHelpers.get_merged_query_parameters(
                         existing_url=url,
-                        request_query_params=dict(request.query_params),
+                        request_query_params=request_params,
+                        default_query_params=default_query_params,
                     )
                 ).encode("ascii")
             )
@@ -1080,6 +1087,7 @@ def create_pass_through_route(
     custom_llm_provider: Optional[str] = None,
     is_streaming_request: Optional[bool] = False,
     query_params: Optional[dict] = None,
+    default_query_params: Optional[dict] = None,
     guardrails: Optional[Dict[str, Any]] = None,
 ):
     # check if target is an adapter.py or a url
@@ -1171,6 +1179,7 @@ def create_pass_through_route(
                 "cost_per_request", cost_per_request
             )
             param_guardrails = target_params.get("guardrails", None)
+            param_default_query_params = target_params.get("default_query_params", None)
 
             # Construct the full target URL with subpath if needed
             full_target = (
@@ -1208,6 +1217,7 @@ def create_pass_through_route(
                 forward_headers=cast(Optional[bool], param_forward_headers),
                 merge_query_params=cast(Optional[bool], param_merge_query_params),
                 query_params=final_query_params,
+                default_query_params=param_default_query_params,
                 stream=is_streaming_request or stream,
                 custom_body=final_custom_body,
                 cost_per_request=cast(Optional[float], param_cost_per_request),
@@ -1849,6 +1859,7 @@ class InitPassThroughEndpointHelpers:
         endpoint_id: str,
         guardrails: Optional[dict] = None,
         methods: Optional[List[str]] = None,
+        default_query_params: Optional[dict] = None,
     ):
         """Add exact path route for pass-through endpoint"""
         # Default to all methods if none specified (backward compatibility)
@@ -1886,6 +1897,7 @@ class InitPassThroughEndpointHelpers:
                 merge_query_params,
                 dependencies,
                 cost_per_request=cost_per_request,
+                default_query_params=default_query_params,
                 guardrails=guardrails,
             ),
             methods=methods,
@@ -1903,6 +1915,7 @@ class InitPassThroughEndpointHelpers:
                 "custom_headers": custom_headers,
                 "forward_headers": forward_headers,
                 "merge_query_params": merge_query_params,
+                "default_query_params": default_query_params,
                 "dependencies": dependencies,
                 "cost_per_request": cost_per_request,
                 "guardrails": guardrails,
@@ -1922,6 +1935,7 @@ class InitPassThroughEndpointHelpers:
         endpoint_id: str,
         guardrails: Optional[dict] = None,
         methods: Optional[List[str]] = None,
+        default_query_params: Optional[dict] = None,
     ):
         """Add wildcard route for sub-paths"""
         # Default to all methods if none specified (backward compatibility)
@@ -1960,6 +1974,7 @@ class InitPassThroughEndpointHelpers:
                 dependencies,
                 include_subpath=True,
                 cost_per_request=cost_per_request,
+                default_query_params=default_query_params,
                 guardrails=guardrails,
             ),
             methods=methods,
@@ -1977,6 +1992,7 @@ class InitPassThroughEndpointHelpers:
                 "custom_headers": custom_headers,
                 "forward_headers": forward_headers,
                 "merge_query_params": merge_query_params,
+                "default_query_params": default_query_params,
                 "dependencies": dependencies,
                 "cost_per_request": cost_per_request,
                 "guardrails": guardrails,
@@ -2170,6 +2186,7 @@ async def initialize_pass_through_endpoints(
         )
         _forward_headers = endpoint.get("forward_headers", None)
         _merge_query_params = endpoint.get("merge_query_params", None)
+        _default_query_params = endpoint.get("default_query_params", None)
         _auth = endpoint.get("auth", None)
         _dependencies = None
         if _auth is not None and str(_auth).lower() == "true":
@@ -2207,6 +2224,7 @@ async def initialize_pass_through_endpoints(
             endpoint_id=endpoint_id,
             guardrails=_guardrails,
             methods=_methods,
+            default_query_params=_default_query_params,
         )
 
         # Generate route key with methods for tracking
@@ -2228,6 +2246,7 @@ async def initialize_pass_through_endpoints(
                 endpoint_id=endpoint_id,
                 guardrails=_guardrails,
                 methods=_methods,
+                default_query_params=_default_query_params,
             )
 
             visited_endpoints.add(f"{endpoint_id}:subpath:{_path}:{methods_str}")
@@ -2546,6 +2565,7 @@ async def update_pass_through_endpoints(
             endpoint_id=updated_endpoint.id or endpoint_id or "",
             guardrails=getattr(updated_endpoint, "guardrails", None),
             methods=updated_endpoint.methods,
+            default_query_params=updated_endpoint.default_query_params,
         )
     else:
         InitPassThroughEndpointHelpers.add_exact_path_route(
@@ -2560,6 +2580,7 @@ async def update_pass_through_endpoints(
             endpoint_id=updated_endpoint.id or endpoint_id or "",
             guardrails=getattr(updated_endpoint, "guardrails", None),
             methods=updated_endpoint.methods,
+            default_query_params=updated_endpoint.default_query_params,
         )
 
     return PassThroughEndpointResponse(
@@ -2637,6 +2658,7 @@ async def create_pass_through_endpoints(
             endpoint_id=created_endpoint.id or "",
             guardrails=getattr(created_endpoint, "guardrails", None),
             methods=created_endpoint.methods,
+            default_query_params=created_endpoint.default_query_params,
         )
     else:
         InitPassThroughEndpointHelpers.add_exact_path_route(
@@ -2651,6 +2673,7 @@ async def create_pass_through_endpoints(
             endpoint_id=created_endpoint.id or "",
             guardrails=getattr(created_endpoint, "guardrails", None),
             methods=created_endpoint.methods,
+            default_query_params=created_endpoint.default_query_params,
         )
 
     return PassThroughEndpointResponse(endpoints=[created_endpoint])