diff --git a/python/ray/serve/_private/deployment_state.py b/python/ray/serve/_private/deployment_state.py
index 37c7a5f90d4c..1671b712d86e 100644
--- a/python/ray/serve/_private/deployment_state.py
+++ b/python/ray/serve/_private/deployment_state.py
@@ -1515,6 +1515,7 @@ class ReplicaStateContainer:
 
     def __init__(self):
         self._replicas: Dict[ReplicaState, List[DeploymentReplica]] = defaultdict(list)
+        self._replica_id_index: Dict[ReplicaID, DeploymentReplica] = {}
 
     def add(self, state: ReplicaState, replica: DeploymentReplica):
         """Add the provided replica under the provided state.
@@ -1526,6 +1527,7 @@ def add(self, state: ReplicaState, replica: DeploymentReplica):
         assert isinstance(state, ReplicaState), f"Type: {type(state)}"
         replica.update_state(state)
         self._replicas[state].append(replica)
+        self._replica_id_index[replica.replica_id] = replica
 
     def get(
         self, states: Optional[List[ReplicaState]] = None
@@ -1540,12 +1542,23 @@ def get(
                 are considered.
         """
         if states is None:
-            states = ALL_REPLICA_STATES
+            return list(self._replica_id_index.values())
 
         assert isinstance(states, list)
 
         return sum((self._replicas[state] for state in states), [])
 
+    def get_by_id(self, replica_id: ReplicaID) -> Optional[DeploymentReplica]:
+        """Get a replica by its ID in O(1) time.
+
+        Args:
+            replica_id: the ID of the replica to look up.
+
+        Returns:
+            The DeploymentReplica if found, else None.
+        """
+        return self._replica_id_index.get(replica_id)
+
     def pop(
         self,
         exclude_version: Optional[DeploymentVersion] = None,
@@ -1587,6 +1600,9 @@ def pop(
             self._replicas[state] = remaining
             replicas.extend(popped)
 
+        for replica in replicas:
+            self._replica_id_index.pop(replica.replica_id, None)
+
         return replicas
 
     def count(
@@ -3496,17 +3512,16 @@ def record_request_routing_info(self, info: RequestRoutingInfo) -> None:
             info: RequestRoutingInfo including deployment name, replica tag,
                 multiplex model ids, and routing stats.
         """
-        # Find the replica
-        for replica in self._replicas.get():
-            if replica.replica_id == info.replica_id:
-                if info.multiplexed_model_ids is not None:
-                    replica.record_multiplexed_model_ids(info.multiplexed_model_ids)
-                if info.routing_stats is not None:
-                    replica.record_routing_stats(info.routing_stats)
-                self._request_routing_info_updated = True
-                return
-
-        logger.warning(f"{info.replica_id} not found.")
+        # O(1) lookup via replica_id index.
+        replica = self._replicas.get_by_id(info.replica_id)
+        if replica is not None:
+            if info.multiplexed_model_ids is not None:
+                replica.record_multiplexed_model_ids(info.multiplexed_model_ids)
+            if info.routing_stats is not None:
+                replica.record_routing_stats(info.routing_stats)
+            self._request_routing_info_updated = True
+        else:
+            logger.warning(f"{info.replica_id} not found.")
 
     def _stop_one_running_replica_for_testing(self):
         running_replicas = self._replicas.pop(states=[ReplicaState.RUNNING])
diff --git a/python/ray/serve/tests/unit/test_deployment_state.py b/python/ray/serve/tests/unit/test_deployment_state.py
index 063ff17e81cc..b359596b417d 100644
--- a/python/ray/serve/tests/unit/test_deployment_state.py
+++ b/python/ray/serve/tests/unit/test_deployment_state.py
@@ -442,6 +442,13 @@ class FakeDeploymentReplica:
 
     def __init__(self, version: DeploymentVersion):
         self._version = version
+        self._replica_id = ReplicaID(
+            get_random_string(), deployment_id=DeploymentID(name="fake")
+        )
+
+    @property
+    def replica_id(self):
+        return self._replica_id
 
     @property
     def version(self):
@@ -532,6 +539,37 @@ def test_get(self):
         assert c.get([ReplicaState.STARTING]) == [r1, r2]
         assert c.get([ReplicaState.STOPPING]) == [r3]
 
+    def test_get_by_id(self):
+        c = ReplicaStateContainer()
+        r1, r2, r3 = replica(), replica(), replica()
+
+        c.add(ReplicaState.STARTING, r1)
+        c.add(ReplicaState.RUNNING, r2)
+        c.add(ReplicaState.STOPPING, r3)
+
+        # Found: each replica is retrievable by its ID regardless of state.
+        assert c.get_by_id(r1.replica_id) is r1
+        assert c.get_by_id(r2.replica_id) is r2
+        assert c.get_by_id(r3.replica_id) is r3
+
+        # Not found: a replica ID that was never added returns None.
+        unknown = replica()
+        assert c.get_by_id(unknown.replica_id) is None
+
+        # After pop: popped replicas are no longer in the index.
+        popped = c.pop(states=[ReplicaState.RUNNING])
+        assert popped == [r2]
+        assert c.get_by_id(r2.replica_id) is None
+
+        # Remaining replicas are still found.
+        assert c.get_by_id(r1.replica_id) is r1
+        assert c.get_by_id(r3.replica_id) is r3
+
+        # Pop everything and verify the index is fully cleared.
+        c.pop()
+        assert c.get_by_id(r1.replica_id) is None
+        assert c.get_by_id(r3.replica_id) is None
+
     def test_pop_basic(self):
         c = ReplicaStateContainer()
         r1, r2, r3 = replica(), replica(), replica()