diff --git a/vllm/v1/core/scheduler.py b/vllm/v1/core/scheduler.py
index 41659ff62747d..6017905642172 100644
--- a/vllm/v1/core/scheduler.py
+++ b/vllm/v1/core/scheduler.py
@@ -246,7 +246,7 @@ def update_from_output(
                 # NOTE(woosuk): Currently, we assume that each request
                 # generates at most one token at each step.
                 token_id = sampled_token_ids[req_index]
-                request.output_token_ids.append(token_id)
+                request.append_output_token_ids(token_id)
                 sampled.append((request, 1))
                 # TODO: Update the KV cache manager for prefix caching.
 
diff --git a/vllm/v1/engine/llm_engine.py b/vllm/v1/engine/llm_engine.py
index 5f5720480abdc..b538c2c7d63bc 100644
--- a/vllm/v1/engine/llm_engine.py
+++ b/vllm/v1/engine/llm_engine.py
@@ -324,7 +324,7 @@ def send_to_detokenizer(self, sampled: List[Tuple[Request, int]]) -> None:
         )
         for req, num_tokens in sampled:
             inputs.req_ids.append(req.request_id)
-            if len(req.output_token_ids) == num_tokens:
+            if req.num_output_tokens == num_tokens:
                 # The request is first detokenized.
                 inputs.prompt_token_ids.append(req.prompt_token_ids)
             else:
diff --git a/vllm/v1/request.py b/vllm/v1/request.py
index be7d4d165d280..087067cdac56f 100644
--- a/vllm/v1/request.py
+++ b/vllm/v1/request.py
@@ -4,6 +4,7 @@
 from vllm.lora.request import LoRARequest
 from vllm.sampling_params import SamplingParams
 from vllm.sequence import RequestMetrics
+from vllm.v1.utils import ConstantList
 
 if TYPE_CHECKING:
     from vllm.inputs import DecoderOnlyInputs
@@ -40,17 +41,39 @@ def __init__(
         self.prompt = inputs.get("prompt")
         self.prompt_token_ids = inputs["prompt_token_ids"]
         self.num_prompt_tokens = len(self.prompt_token_ids)
-        self.output_token_ids: List[int] = []
+        self._output_token_ids: List[int] = []
+        self._all_token_ids: List[int] = self.prompt_token_ids.copy()
         self.output_text = ""
         self.num_computed_tokens = 0
 
+    @property
+    def output_token_ids(self) -> ConstantList[int]:
+        # Prevent directly appending to the output_token_ids since
+        # all_token_ids should also be updated simultaneously.
+        return ConstantList(self._output_token_ids)
+
+    @property
+    def all_token_ids(self) -> ConstantList[int]:
+        # Prevent directly appending to the all_token_ids since
+        # output_token_ids should also be updated simultaneously
+        return ConstantList(self._all_token_ids)
+
+    def append_output_token_ids(
+        self,
+        token_ids: Union[int, List[int]],
+    ) -> None:
+        if isinstance(token_ids, int):
+            token_ids = [token_ids]
+        self._output_token_ids.extend(token_ids)
+        self._all_token_ids.extend(token_ids)
+
     @property
     def num_tokens(self) -> int:
-        return self.num_prompt_tokens + len(self.output_token_ids)
+        return len(self._all_token_ids)
 
     @property
     def num_output_tokens(self) -> int:
-        return len(self.output_token_ids)
+        return len(self._output_token_ids)
 
     def is_finished(self) -> bool:
         return RequestStatus.is_finished(self.status)
diff --git a/vllm/v1/utils.py b/vllm/v1/utils.py
new file mode 100644
index 0000000000000..4b26749712e32
--- /dev/null
+++ b/vllm/v1/utils.py
@@ -0,0 +1,64 @@
+from typing import Generic, List, TypeVar, overload
+
+T = TypeVar("T")
+
+
+class ConstantList(Generic[T]):
+
+    def __init__(self, x: List[T]) -> None:
+        self._x = x
+
+    def append(self, item):
+        raise Exception("Cannot append to a constant list")
+
+    def extend(self, item):
+        raise Exception("Cannot extend a constant list")
+
+    def insert(self, item):
+        raise Exception("Cannot insert into a constant list")
+
+    def pop(self, item):
+        raise Exception("Cannot pop from a constant list")
+
+    def remove(self, item):
+        raise Exception("Cannot remove from a constant list")
+
+    def clear(self):
+        raise Exception("Cannot clear a constant list")
+
+    def index(self, item):
+        return self._x.index(item)
+
+    @overload
+    def __getitem__(self, item) -> T:
+        ...
+
+    @overload
+    def __getitem__(self, s: slice, /) -> List[T]:
+        ...
+
+    def __getitem__(self, item):
+        return self._x[item]
+
+    @overload
+    def __setitem__(self, item, value):
+        ...
+
+    @overload
+    def __setitem__(self, s: slice, value, /):
+        ...
+
+    def __setitem__(self, item, value):
+        raise Exception("Cannot set item in a constant list")
+
+    def __delitem__(self, item):
+        raise Exception("Cannot delete item from a constant list")
+
+    def __iter__(self):
+        return iter(self._x)
+
+    def __contains__(self, item):
+        return item in self._x
+
+    def __len__(self):
+        return len(self._x)