diff --git a/vllm/distributed/eplb/policy/abstract.py b/vllm/distributed/eplb/policy/abstract.py
index 40ed621c84892..f4435f11bd57b 100644
--- a/vllm/distributed/eplb/policy/abstract.py
+++ b/vllm/distributed/eplb/policy/abstract.py
@@ -16,6 +16,7 @@ class AbstractEplbPolicy(ABC):
         num_groups: int,
         num_nodes: int,
         num_ranks: int,
+        old_global_expert_indices: torch.Tensor | None = None,
     ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor]:
         """
         Entry point for expert-parallelism load balancer.
@@ -28,7 +29,9 @@ class AbstractEplbPolicy(ABC):
             num_groups: number of expert groups
             num_nodes: number of server nodes
             num_ranks: number of ranks, must be a multiple of `num_nodes`
-
+            old_global_expert_indices: [layers, num_logical_experts], the old global
+                expert indices. Used to avoid unnecessary weight copying
+                for experts moving within one rank.
         Returns:
             physical_to_logical_map: [layers, num_replicas], the expert
                 index of each replica
diff --git a/vllm/distributed/eplb/policy/default.py b/vllm/distributed/eplb/policy/default.py
index 82fd1b94acaea..970a1614933ee 100644
--- a/vllm/distributed/eplb/policy/default.py
+++ b/vllm/distributed/eplb/policy/default.py
@@ -328,7 +328,9 @@ class DefaultEplbPolicy(AbstractEplbPolicy):
             num_nodes: number of server nodes, where the intra-node network
                 (e.g, NVLink) is faster
             num_ranks: number of ranks, must be a multiple of `num_nodes`
-
+            old_global_expert_indices: [layers, num_logical_experts], the old global
+                expert indices. Used to avoid unnecessary weight copying
+                for experts moving within one rank.
         Returns:
             phy2log: [layers, num_replicas], the expert
                 index of each replica