diff --git a/vllm/entrypoints/generate/beam_search/offline.py b/vllm/entrypoints/generate/beam_search/offline.py
index b38830d6e41..e1bceb5d23d 100644
--- a/vllm/entrypoints/generate/beam_search/offline.py
+++ b/vllm/entrypoints/generate/beam_search/offline.py
@@ -207,7 +207,9 @@ class BeamSearchOfflineMixin(OfflineInferenceMixin):
         Returns True if all beams are exhausted and search should stop.
         """
         all_beams: list[BeamSearchSequence] = list(
-            sum((instance.beams for instance in instances_batch), [])
+            itertools.chain.from_iterable(
+                instance.beams for instance in instances_batch
+            )
         )
         pos = [0] + list(
             itertools.accumulate(len(instance.beams) for instance in instances_batch)