diff --git a/python/sglang/srt/layers/attention/flashattention_backend.py b/python/sglang/srt/layers/attention/flashattention_backend.py
index a2425f1a2..040393c17 100644
--- a/python/sglang/srt/layers/attention/flashattention_backend.py
+++ b/python/sglang/srt/layers/attention/flashattention_backend.py
@@ -383,7 +383,7 @@ class FlashAttentionBackend(AttentionBackend):
                 forward_batch.req_pool_indices, : metadata.max_seq_len_k
             ]
 
-        elif forward_batch.forward_mode.is_extend_or_draft_extend():
+        elif forward_batch.forward_mode.is_extend_or_draft_extend_or_mixed():
             metadata.cache_seqlens_int32 = seqlens_in_batch.to(torch.int32)
             metadata.max_seq_len_k = forward_batch.seq_lens_cpu.max().item()
             metadata.cu_seqlens_k = torch.nn.functional.pad(
diff --git a/python/sglang/srt/model_executor/forward_batch_info.py b/python/sglang/srt/model_executor/forward_batch_info.py
index a0ead1784..ba861b850 100644
--- a/python/sglang/srt/model_executor/forward_batch_info.py
+++ b/python/sglang/srt/model_executor/forward_batch_info.py
@@ -78,7 +78,7 @@ class ForwardMode(IntEnum):
             self == ForwardMode.EXTEND
             or self == ForwardMode.MIXED
             or self == ForwardMode.DRAFT_EXTEND
-            or self == self.TARGET_VERIFY
+            or self == ForwardMode.TARGET_VERIFY
         )
 
     def is_decode(self):
@@ -96,6 +96,13 @@ class ForwardMode(IntEnum):
     def is_draft_extend(self):
         return self == ForwardMode.DRAFT_EXTEND
 
+    def is_extend_or_draft_extend_or_mixed(self):
+        return (
+            self == ForwardMode.EXTEND
+            or self == ForwardMode.DRAFT_EXTEND
+            or self == ForwardMode.MIXED
+        )
+
     def is_cuda_graph(self):
         return (
             self == ForwardMode.DECODE
@@ -103,9 +110,6 @@ class ForwardMode(IntEnum):
             or self == ForwardMode.IDLE
         )
 
-    def is_extend_or_draft_extend(self):
-        return self == ForwardMode.EXTEND or self == ForwardMode.DRAFT_EXTEND
-
     def is_dummy_first(self):
         return self == ForwardMode.DUMMY_FIRST
 
diff --git a/python/sglang/srt/model_executor/model_runner.py b/python/sglang/srt/model_executor/model_runner.py
index 995c613ce..41a245a10 100644
--- a/python/sglang/srt/model_executor/model_runner.py
+++ b/python/sglang/srt/model_executor/model_runner.py
@@ -78,9 +78,11 @@ from sglang.srt.utils import (
     get_available_gpu_memory,
     init_custom_process_group,
     is_cuda,
+    is_fa3_default_architecture,
     is_flashinfer_available,
     is_hip,
     is_hopper_with_cuda_12_3,
+    is_no_spec_infer_or_topk_one,
     monkey_patch_p2p_access_check,
     monkey_patch_vllm_gguf_config,
     set_cpu_offload_max_bytes,
@@ -242,18 +244,21 @@ class ModelRunner:
         elif server_args.attention_backend is None:
             # By default, use flashinfer for non-mla attention and triton for mla attention
             if not self.use_mla_backend:
-                server_args.attention_backend = (
-                    "flashinfer" if is_flashinfer_available() else "triton"
-                )
+                if (
+                    is_hopper_with_cuda_12_3()
+                    and is_no_spec_infer_or_topk_one(server_args)
+                    and is_fa3_default_architecture(self.model_config.hf_config)
+                ):
+                    server_args.attention_backend = "fa3"
+                else:
+                    server_args.attention_backend = (
+                        "flashinfer" if is_flashinfer_available() else "triton"
+                    )
             else:
-                if is_hopper_with_cuda_12_3():
-                    if server_args.speculative_eagle_topk is None or (
-                        server_args.speculative_eagle_topk is not None
-                        and server_args.speculative_eagle_topk == 1
-                    ):
-                        server_args.attention_backend = "fa3"
-                    else:
-                        server_args.attention_backend = "triton"
+                if is_hopper_with_cuda_12_3() and is_no_spec_infer_or_topk_one(
+                    server_args
+                ):
+                    server_args.attention_backend = "fa3"
                 else:
                     server_args.attention_backend = "triton"
             logger.info(
diff --git a/python/sglang/srt/utils.py b/python/sglang/srt/utils.py
index 0deea5be3..e812a7802 100644
--- a/python/sglang/srt/utils.py
+++ b/python/sglang/srt/utils.py
@@ -569,7 +569,7 @@ def encode_video(video_path, frame_count_limit=None):
 
 
 def load_image(
-    image_file: Union[Image.Image, str, bytes]
+    image_file: Union[Image.Image, str, bytes],
 ) -> tuple[Image.Image, tuple[int, int]]:
     image = image_size = None
     if isinstance(image_file, Image.Image):
@@ -1905,3 +1905,28 @@ def get_local_ip_by_remote() -> str:
         return s.getsockname()[0]
     except Exception:
         raise ValueError(f"Can not get local ip")
+
+
+def is_page_size_one(server_args):
+    return server_args.page_size == 1
+
+
+def is_no_spec_infer_or_topk_one(server_args):
+    return server_args.speculative_eagle_topk is None or (
+        server_args.speculative_eagle_topk is not None
+        and server_args.speculative_eagle_topk == 1
+        and is_page_size_one(server_args)
+    )
+
+
+def is_fa3_default_architecture(hf_config):
+    architectures = getattr(hf_config, "architectures", None)
+    if not isinstance(architectures, list) or not architectures:
+        return False
+    default_archs = {
+        "Qwen2ForCausalLM",
+        "Llama4ForConditionalGeneration",
+        "LlamaForCausalLM",
+        "MistralForCausalLM",
+    }
+    return architectures[0] in default_archs