diff --git a/changelog/unreleased/SOLR-18298-zk-reconnect-session-expiry.yml b/changelog/unreleased/SOLR-18298-zk-reconnect-session-expiry.yml
new file mode 100644
index 000000000000..e9f6f4527c43
--- /dev/null
+++ b/changelog/unreleased/SOLR-18298-zk-reconnect-session-expiry.yml
@@ -0,0 +1,8 @@
+title: ZkController no longer treats every ZooKeeper reconnect as session expiration. Re-election and core re-registration now run only after Curator reports ConnectionState.LOST, restoring Solr 9 behavior during ZK rolling restarts.
+type: fixed
+authors:
+  - name: Shrey Narayan (NextBrick)
+    url: https://nextbrick.com
+links:
+  - name: SOLR-18298
+    url: https://issues.apache.org/jira/browse/SOLR-18298
diff --git a/solr/core/src/java/org/apache/solr/cloud/ZkController.java b/solr/core/src/java/org/apache/solr/cloud/ZkController.java
index 3ab82e68b1d6..c94218056294 100644
--- a/solr/core/src/java/org/apache/solr/cloud/ZkController.java
+++ b/solr/core/src/java/org/apache/solr/cloud/ZkController.java
@@ -402,6 +402,9 @@ public ZkController(
   }
 
   private void onDisconnect(boolean sessionExpired) {
+    if (!sessionExpired) {
+      return;
+    }
     try {
       overseer.close();
     } catch (Exception e) {
diff --git a/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnDisconnect.java b/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnDisconnect.java
index 9535a59cef55..b178c41c9aed 100644
--- a/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnDisconnect.java
+++ b/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnDisconnect.java
@@ -20,13 +20,21 @@
 import org.apache.curator.framework.state.ConnectionState;
 import org.apache.curator.framework.state.ConnectionStateListener;
 
+/**
+ * Listener for ZooKeeper session loss.
+ *
+ * <p>When registered as a Curator {@link ConnectionStateListener}, {@link #onDisconnect(boolean)}
+ * runs only after session expiration ({@link ConnectionState#LOST}). A transient {@link
+ * ConnectionState#SUSPENDED} keeps the session and must not tear down SolrCloud leadership. See
+ * SOLR-18298.
+ */
 public interface OnDisconnect extends ConnectionStateListener {
   void onDisconnect(boolean sessionExpired);
 
   @Override
   default void stateChanged(CuratorFramework client, ConnectionState newState) {
-    if (newState == ConnectionState.LOST || newState == ConnectionState.SUSPENDED) {
-      onDisconnect(newState == ConnectionState.LOST);
+    if (newState == ConnectionState.LOST) {
+      onDisconnect(true);
     }
   }
 }
diff --git a/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnReconnect.java b/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnReconnect.java
index 8d54312d3e0f..88f95efffea7 100644
--- a/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnReconnect.java
+++ b/solr/solrj-zookeeper/src/java/org/apache/solr/common/cloud/OnReconnect.java
@@ -16,6 +16,9 @@
  */
 package org.apache.solr.common.cloud;
 
+import java.util.Collections;
+import java.util.Set;
+import java.util.WeakHashMap;
 import org.apache.curator.framework.CuratorFramework;
 import org.apache.curator.framework.state.ConnectionState;
 import org.apache.curator.framework.state.ConnectionStateListener;
@@ -26,14 +29,36 @@
  * implementation should call
  * org.apache.solr.cloud.ZkController#removeOnReconnectListener(OnReconnect) when it no longer needs
  * to be notified of ZK reconnection events.
+ *
+ * <p>When registered as a Curator {@link ConnectionStateListener}, {@link #onReconnect()} runs only
+ * after a session expiration ({@link ConnectionState#LOST} then {@link
+ * ConnectionState#RECONNECTED}). A reconnect after {@link ConnectionState#SUSPENDED} keeps the
+ * ZooKeeper session and must not trigger SolrCloud recovery. See SOLR-18298.
  */
 public interface OnReconnect extends ConnectionStateListener {
   void onReconnect();
 
   @Override
   default void stateChanged(CuratorFramework client, ConnectionState newState) {
-    if (ConnectionState.RECONNECTED.equals(newState)) {
+    if (newState == ConnectionState.LOST) {
+      LostSessions.mark(this);
+    } else if (newState == ConnectionState.RECONNECTED && LostSessions.consume(this)) {
       onReconnect();
     }
   }
+
+  /** Tracks listeners that have observed {@link ConnectionState#LOST} and still need reconnect. */
+  final class LostSessions {
+    private static final Set<OnReconnect> lost = Collections.newSetFromMap(new WeakHashMap<>());
+
+    private LostSessions() {}
+
+    static synchronized void mark(OnReconnect listener) {
+      lost.add(listener);
+    }
+
+    static synchronized boolean consume(OnReconnect listener) {
+      return lost.remove(listener);
+    }
+  }
 }
diff --git a/solr/solrj-zookeeper/src/test/org/apache/solr/common/cloud/TestOnReconnectSessionExpiry.java b/solr/solrj-zookeeper/src/test/org/apache/solr/common/cloud/TestOnReconnectSessionExpiry.java
new file mode 100644
index 000000000000..9d6c83fa65af
--- /dev/null
+++ b/solr/solrj-zookeeper/src/test/org/apache/solr/common/cloud/TestOnReconnectSessionExpiry.java
@@ -0,0 +1,70 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.solr.common.cloud;
+
+import java.util.concurrent.atomic.AtomicInteger;
+import org.apache.curator.framework.state.ConnectionState;
+import org.apache.solr.SolrTestCase;
+import org.junit.Test;
+
+/** SOLR-18298: Curator RECONNECTED is not the same as Solr 9 session-expiration reconnect. */
+public class TestOnReconnectSessionExpiry extends SolrTestCase {
+
+  @Test
+  public void testReconnectAfterSuspendDoesNotFire() {
+    AtomicInteger reconnects = new AtomicInteger();
+    OnReconnect listener = () -> reconnects.incrementAndGet();
+
+    listener.stateChanged(null, ConnectionState.SUSPENDED);
+    listener.stateChanged(null, ConnectionState.RECONNECTED);
+
+    assertEquals(0, reconnects.get());
+  }
+
+  @Test
+  public void testReconnectAfterLostDoesFire() {
+    AtomicInteger reconnects = new AtomicInteger();
+    OnReconnect listener = () -> reconnects.incrementAndGet();
+
+    listener.stateChanged(null, ConnectionState.LOST);
+    listener.stateChanged(null, ConnectionState.RECONNECTED);
+
+    assertEquals(1, reconnects.get());
+  }
+
+  @Test
+  public void testReconnectWithoutPriorLostDoesNotFire() {
+    AtomicInteger reconnects = new AtomicInteger();
+    OnReconnect listener = () -> reconnects.incrementAndGet();
+
+    listener.stateChanged(null, ConnectionState.RECONNECTED);
+
+    assertEquals(0, reconnects.get());
+  }
+
+  @Test
+  public void testDisconnectFiresOnlyOnLost() {
+    AtomicInteger disconnects = new AtomicInteger();
+    OnDisconnect listener = sessionExpired -> disconnects.incrementAndGet();
+
+    listener.stateChanged(null, ConnectionState.SUSPENDED);
+    assertEquals(0, disconnects.get());
+
+    listener.stateChanged(null, ConnectionState.LOST);
+    assertEquals(1, disconnects.get());
+  }
+}