diff --git a/vllm/v1/engine/__init__.py b/vllm/v1/engine/__init__.py
index 3f621d77c024..ce2aae77108d 100644
--- a/vllm/v1/engine/__init__.py
+++ b/vllm/v1/engine/__init__.py
@@ -72,6 +72,14 @@ class EngineCoreRequest(
 
     trace_headers: Mapping[str, str] | None = None
 
+    @property
+    def params(self) -> SamplingParams | PoolingParams:
+        """Return the processed params (sampling or pooling)."""
+        if self.sampling_params is not None:
+            return self.sampling_params
+        assert self.pooling_params is not None
+        return self.pooling_params
+
 
 class EngineCoreEventType(enum.IntEnum):
     """The type of engine core request event."""
diff --git a/vllm/v1/engine/async_llm.py b/vllm/v1/engine/async_llm.py
index c64b3cccfc65..55087baadff9 100644
--- a/vllm/v1/engine/async_llm.py
+++ b/vllm/v1/engine/async_llm.py
@@ -321,14 +321,15 @@ class AsyncLLM(EngineClient):
             elif isinstance(prompt, Mapping):
                 prompt_text = cast(str | None, prompt.get("prompt"))
 
+        # Use cloned params that may have been updated in process_inputs()
+        params = request.params
+
         if is_pooling or params.n == 1:
             await self._add_request(request, prompt_text, None, 0, queue)
             return queue
 
-        # Get the updated SamplingParams from the request, which
-        # were cloned/updated in processor.process_inputs above.
-        parent_params = request.sampling_params
-        assert parent_params is not None
+        parent_params = params
+        assert isinstance(parent_params, SamplingParams)
 
         # Fan out child requests (for n>1).
         parent_request = ParentRequest(request_id, parent_params)
diff --git a/vllm/v1/engine/llm_engine.py b/vllm/v1/engine/llm_engine.py
index e403cea87788..dffe05445ee4 100644
--- a/vllm/v1/engine/llm_engine.py
+++ b/vllm/v1/engine/llm_engine.py
@@ -250,6 +250,9 @@ class LLMEngine:
             elif isinstance(prompt, Mapping):
                 prompt_text = cast(str | None, prompt.get("prompt"))
 
+        # Use cloned params that may have been updated in process_inputs()
+        params = request.params
+
         n = params.n if isinstance(params, SamplingParams) else 1
 
         if n == 1:
@@ -262,10 +265,10 @@ class LLMEngine:
         # Fan out child requests (for n>1).
         parent_req = ParentRequest(request_id, params)
         for idx in range(n):
-            request_id, params = parent_req.get_child_info(idx)
+            request_id, child_params = parent_req.get_child_info(idx)
             child_request = request if idx == n - 1 else copy(request)
             child_request.request_id = request_id
-            child_request.sampling_params = params
+            child_request.sampling_params = child_params
 
             # Make a new RequestState and queue.
             self.output_processor.add_request(