diff --git a/serve/mlc_serve/engine/engine_common.py b/serve/mlc_serve/engine/engine_common.py
index 675e97e173..4d40899ab5 100644
--- a/serve/mlc_serve/engine/engine_common.py
+++ b/serve/mlc_serve/engine/engine_common.py
@@ -25,6 +25,7 @@
     ConversationTemplate,
     KVCacheManager,
     ModelModule,
+    RequestType,
     TextGenerator,
     Tokenizer as TokenizerP,
 )
@@ -226,8 +227,8 @@ def update_sequence(
 
 def get_requests_to_process(
     current_states: list[RequestState], cache_manager: KVCacheManager
-) -> Tuple[list[Union[PrefillRequest, DecodeRequest]], bool, int]:
-    requests: list[Union[PrefillRequest, DecodeRequest]] = []
+) -> Tuple[list[RequestType], bool, int]:
+    requests: list[RequestType] = []
     # TODO: consider having hybrid batch if the underlying attention kernel supports
     # mixing prefill and decode.
     is_prompt_batch = any(not state.is_prefilled for state in current_states)
diff --git a/serve/mlc_serve/model/dummy_model.py b/serve/mlc_serve/model/dummy_model.py
index 630ed7c267..b8900273a6 100644
--- a/serve/mlc_serve/model/dummy_model.py
+++ b/serve/mlc_serve/model/dummy_model.py
@@ -11,6 +11,7 @@
     DecodeRequest,
     KVCache,
     PrefillRequest,
+    RequestType,
     SequenceId,
     TextGenerationResult,
 )
@@ -97,7 +98,7 @@ def get_max_new_tokens(self) -> int:
 class DummyTextGenerator:
     def generate(
         self,
-        requests: list[Union[PrefillRequest, DecodeRequest]],
+        requests: list[RequestType],
         kv_cache: DummyCache,
     ) -> list[TextGenerationResult]:
         result = []
diff --git a/serve/mlc_serve/model/paged_cache_model.py b/serve/mlc_serve/model/paged_cache_model.py
index 7daf3336f4..6c45621dcb 100644
--- a/serve/mlc_serve/model/paged_cache_model.py
+++ b/serve/mlc_serve/model/paged_cache_model.py
@@ -12,6 +12,7 @@
     DecodeRequest,
     ModelModule,
     PrefillRequest,
+    RequestType,
     TextGenerationResult,
     TextGenerator,
 )
@@ -24,7 +25,7 @@ def __init__(self, model: TextGenerator):
         self.model = model
 
     def generate(
-        self, requests: List[Union[PrefillRequest, DecodeRequest]], kv_cache
+        self, requests: List[RequestType], kv_cache
     ) -> List[TextGenerationResult]:
         prefill_requests = [r for r in requests if isinstance(r, PrefillRequest)]
         decode_requests = [r for r in requests if isinstance(r, DecodeRequest)]