[Bug] Fix attention_backend arg string parsing (#30534)

Signed-off-by: mgoin <mgoin64@gmail.com>

[Bug] Fix attention_backend arg string parsing (#30534)
Signed-off-by: mgoin <mgoin64@gmail.com>
09ad3b76 · Michael Goin · GitHub · dc13c99e · 09ad3b76
Unverified Commit 09ad3b76 authored Dec 12, 2025 by Michael Goin Committed by GitHub Dec 12, 2025
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vllm/engine/arg_utils.py vllm/engine/arg_utils.py +7 -1

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--- a/vllm/engine/arg_utils.py
+++ b/vllm/engine/arg_utils.py
@@ -1649,7 +1649,13 @@ class EngineArgs:
                    "attention_backend and attention_config.backend "
                    "are mutually exclusive"
                )
-            attention_config.backend = self.attention_backend
+            # Convert string to enum if needed (CLI parsing returns a string)
+            if isinstance(self.attention_backend, str):
+                attention_config.backend = AttentionBackendEnum[
+                    self.attention_backend.upper()
+                ]
+            else:
+                attention_config.backend = self.attention_backend

        load_config = self.create_load_config()