diff --git a/miles/backends/sglang_utils/arguments.py b/miles/backends/sglang_utils/arguments.py
index 71e3f48fb4..153286b1ee 100644
--- a/miles/backends/sglang_utils/arguments.py
+++ b/miles/backends/sglang_utils/arguments.py
@@ -147,6 +147,13 @@ def validate_args(args):
     if args.sglang_dp_size > 1:
         assert args.sglang_enable_dp_attention
 
+    from miles.utils.environ import enable_experimental_rollout_refactor
+
+    if args.sglang_router_policy is None and args.use_session_server and not enable_experimental_rollout_refactor():
+        args.sglang_router_policy = "manual"
+        if args.router_assignment_mode == "random":
+            args.router_assignment_mode = "min_load"
+
     if args.sglang_router_policy:
         from miles.utils.environ import enable_experimental_rollout_refactor
 
diff --git a/miles/rollout/sglang_rollout.py b/miles/rollout/sglang_rollout.py
index 64662ed522..cd8b8de58f 100644
--- a/miles/rollout/sglang_rollout.py
+++ b/miles/rollout/sglang_rollout.py
@@ -194,7 +194,7 @@ async def generate(args: Namespace, sample: Sample, sampling_params: dict[str, A
 
     # Use session_id for consistent hashing routing if router uses consistent_hashing policy
     headers = None
-    if args.sglang_router_policy == "consistent_hashing" and sample.session_id:
+    if args.sglang_router_policy in ("consistent_hashing", "manual") and sample.session_id:
         headers = {"X-SMG-Routing-Key": sample.session_id}
 
     output = await post(url, payload, headers=headers)
@@ -314,7 +314,7 @@ async def generate_and_rm_group(
         return group
 
     # Generate a unique session_id for each sample in the group (consistent hashing only)
-    if args.sglang_router_policy == "consistent_hashing":
+    if args.sglang_router_policy in ("consistent_hashing", "manual"):
         for sample in group:
             if sample.session_id is None:
                 sample.session_id = str(uuid.uuid4())