[core/model] Use explicit model arch for Llama4 attention backend auto-selection (#24232)

python/sglang/srt/server_args.py

@@ -81,6 +81,10 @@ MIMO_V2_MODEL_ARCHS = (
     "MiMoV2ForCausalLM",
     "MiMoV2FlashForCausalLM",
 )
+LLAMA4_MODEL_ARCHS = (
+    "Llama4ForConditionalGeneration",
+    "Llama4ForCausalLM",
+)
 
 SAMPLING_BACKEND_CHOICES = {"flashinfer", "pytorch", "ascend"}
 
@@ -2034,7 +2038,7 @@ class ServerArgs:
                 logger.warning(
                     "Disable hybrid SWA memory for Step3p5ForCausalLM model with hierarchical cache"
                 )
-        elif "Llama4" in model_arch and self.device != "cpu":
+        elif model_arch in LLAMA4_MODEL_ARCHS and self.device != "cpu":
             # Auto-select attention backend for Llama4 if not specified
             if self.attention_backend is None:
                 if is_sm100_supported():