[misc] soft drop beam search (#8763)

vllm/envs.py

@@ -62,6 +62,7 @@ if TYPE_CHECKING:
     VLLM_TORCH_PROFILER_DIR: Optional[str] = None
     VLLM_USE_TRITON_AWQ: bool = False
     VLLM_ALLOW_RUNTIME_LORA_UPDATING: bool = False
+    VLLM_ALLOW_DEPRECATED_BEAM_SEARCH: bool = False
 
 
 def get_default_cache_root():
@@ -195,6 +196,10 @@ environment_variables: Dict[str, Callable[[], Any]] = {
     lambda: (os.environ.get("VLLM_USE_TRITON_FLASH_ATTN", "True").lower() in
              ("true", "1")),
 
+    # If set, allowing the use of deprecated beam search implementation
+    "VLLM_ALLOW_DEPRECATED_BEAM_SEARCH":
+    lambda: os.environ.get("VLLM_ALLOW_DEPRECATED_BEAM_SEARCH", "0") == "1",
+
     # Internal flag to enable Dynamo graph capture
     "VLLM_TEST_DYNAMO_GRAPH_CAPTURE":
     lambda: int(os.environ.get("VLLM_TEST_DYNAMO_GRAPH_CAPTURE", "0")),