diff --git a/tests/entrypoints/openai/responses/test_function_call.py b/tests/entrypoints/openai/responses/test_function_call.py
index 8ca43feaca4f..9dcbd74c890b 100644
--- a/tests/entrypoints/openai/responses/test_function_call.py
+++ b/tests/entrypoints/openai/responses/test_function_call.py
@@ -325,8 +325,12 @@ async def test_function_calling_with_streaming_expected_arguments(
     "tool_choice",
     ["auto", "required", {"type": "function", "name": "get_current_weather"}],
 )
+@pytest.mark.parametrize(
+    "enable_thinking",
+    [True, False],
+)
 async def test_function_calling_with_streaming_types(
-    client: openai.AsyncOpenAI, model_name: str, tool_choice
+    client: openai.AsyncOpenAI, model_name: str, tool_choice, enable_thinking: bool
 ):
     # this links the "done" type with the "start" type
     # so every "done" type should have a corresponding "start" type
@@ -436,6 +440,7 @@ async def test_function_calling_with_streaming_types(
         input=input_list,
         tools=tools,
         tool_choice=tool_choice,
+        extra_body={"chat_template_kwargs": {"enable_thinking": enable_thinking}},
         stream=True,
     )
 
diff --git a/vllm/entrypoints/openai/generate/api_router.py b/vllm/entrypoints/openai/generate/api_router.py
index 4386baa14e10..84a7fddeabe3 100644
--- a/vllm/entrypoints/openai/generate/api_router.py
+++ b/vllm/entrypoints/openai/generate/api_router.py
@@ -103,6 +103,7 @@ async def init_generate_state(
             enable_prompt_tokens_details=args.enable_prompt_tokens_details,
             enable_force_include_usage=args.enable_force_include_usage,
             enable_log_outputs=args.enable_log_outputs,
+            default_chat_template_kwargs=args.default_chat_template_kwargs,
         )
         if "generate" in supported_tasks
         else None
diff --git a/vllm/entrypoints/openai/responses/protocol.py b/vllm/entrypoints/openai/responses/protocol.py
index b5d69ea1cccc..10aa5bde392b 100644
--- a/vllm/entrypoints/openai/responses/protocol.py
+++ b/vllm/entrypoints/openai/responses/protocol.py
@@ -276,6 +276,13 @@ class ResponsesRequest(OpenAIBaseModel):
         default=None,
         description="KVTransfer parameters used for disaggregated serving.",
     )
+    chat_template_kwargs: dict[str, Any] | None = Field(
+        default=None,
+        description=(
+            "Additional keyword args to pass to the chat template renderer. "
+            "Will be accessible by the template."
+        ),
+    )
     # --8<-- [end:responses-extra-params]
 
     def build_chat_params(
@@ -296,7 +303,7 @@ def build_chat_params(
             chat_template=default_template,
             chat_template_content_format=default_template_content_format,
             chat_template_kwargs=merge_kwargs(  # To remove unset values
-                {},
+                self.chat_template_kwargs,
                 dict(
                     add_generation_prompt=not continue_final,
                     continue_final_message=continue_final,
diff --git a/vllm/entrypoints/openai/responses/serving.py b/vllm/entrypoints/openai/responses/serving.py
index fb28a2256ad0..92b19f175ced 100644
--- a/vllm/entrypoints/openai/responses/serving.py
+++ b/vllm/entrypoints/openai/responses/serving.py
@@ -167,6 +167,7 @@ def __init__(
         enable_prompt_tokens_details: bool = False,
         enable_force_include_usage: bool = False,
         enable_log_outputs: bool = False,
+        default_chat_template_kwargs: dict[str, Any] | None = None,
     ) -> None:
         super().__init__(
             engine_client=engine_client,
@@ -178,6 +179,7 @@ def __init__(
         self.openai_serving_render = openai_serving_render
         self.chat_template = chat_template
         self.chat_template_content_format: Final = chat_template_content_format
+        self.chat_template_kwargs = default_chat_template_kwargs or {}
         self.enable_log_outputs = enable_log_outputs
 
         # Set up the unified parser - either a unified parser or fall back to
@@ -254,10 +256,14 @@ def __init__(
     def _effective_chat_template_kwargs(
         self, request: ResponsesRequest
     ) -> dict[str, Any]:
-        return request.build_chat_params(
-            self.chat_template,
-            self.chat_template_content_format,
-        ).chat_template_kwargs
+        return (
+            request.build_chat_params(
+                self.chat_template,
+                self.chat_template_content_format,
+            )
+            .with_defaults(self.chat_template_kwargs)
+            .chat_template_kwargs
+        )
 
     def _validate_generator_input(
         self,
@@ -601,13 +607,13 @@ async def _make_request(
             prev_msg=self.msg_store.get(prev_response.id) if prev_response else None,
             prev_response_output=prev_response.output if prev_response else None,
         )
-
+        chat_template_kwargs = self._effective_chat_template_kwargs(request)
         _, engine_inputs = await self.openai_serving_render.preprocess_chat(
             request,
             messages,
             default_template=self.chat_template,
             default_template_content_format=self.chat_template_content_format,
-            default_template_kwargs=None,
+            default_template_kwargs=chat_template_kwargs,
             tool_dicts=tool_dicts,
             tool_parser=self.parser.tool_parser_cls if self.parser else None,
             reasoning_parser=self.parser.reasoning_parser_cls if self.parser else None,
@@ -626,13 +632,13 @@ async def _render_next_turn(
         new_messages = construct_input_messages(
             request_input=messages,
         )
-
+        chat_template_kwargs = self._effective_chat_template_kwargs(request)
         _, engine_inputs = await self.openai_serving_render.preprocess_chat(
             request,
             new_messages,
             default_template=chat_template,
             default_template_content_format=chat_template_content_format,
-            default_template_kwargs=None,
+            default_template_kwargs=chat_template_kwargs,
             tool_dicts=tool_dicts,
             tool_parser=tool_parser,
             reasoning_parser=self.parser.reasoning_parser_cls if self.parser else None,