diff --git a/clients/src/main/resources/common/message/JoinGroupRequest.json b/clients/src/main/resources/common/message/JoinGroupRequest.json
index 41d7c1acbae..31afdb1a32a 100644
--- a/clients/src/main/resources/common/message/JoinGroupRequest.json
+++ b/clients/src/main/resources/common/message/JoinGroupRequest.json
@@ -18,8 +18,6 @@
   "type": "request",
   "listeners": ["broker"],
   "name": "JoinGroupRequest",
-  // Versions 0-1 were removed in Apache Kafka 4.0, Version 2 is the new baseline.
-  //
   // Version 1 adds RebalanceTimeoutMs. Version 2 and 3 are the same as version 1.
   //
   // Starting from version 4, the client needs to issue a second request to join group
@@ -34,7 +32,7 @@
   // Version 8 adds the Reason field (KIP-800).
   //
   // Version 9 is the same as version 8.
-  "validVersions": "2-9",
+  "validVersions": "0-9",
   "flexibleVersions": "6+",
   "fields": [
     { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
diff --git a/clients/src/main/resources/common/message/JoinGroupResponse.json b/clients/src/main/resources/common/message/JoinGroupResponse.json
index 364309596eb..d2f016f62f6 100644
--- a/clients/src/main/resources/common/message/JoinGroupResponse.json
+++ b/clients/src/main/resources/common/message/JoinGroupResponse.json
@@ -17,8 +17,6 @@
   "apiKey": 11,
   "type": "response",
   "name": "JoinGroupResponse",
-  // Versions 0-1 were removed in Apache Kafka 4.0, Version 2 is the new baseline.
-  //
   // Version 1 is the same as version 0.
   //
   // Version 2 adds throttle time.
@@ -37,7 +35,7 @@
   // Version 8 is the same as version 7.
   //
   // Version 9 adds the SkipAssignment field.
-  "validVersions": "2-9",
+  "validVersions": "0-9",
   "flexibleVersions": "6+",
   "fields": [
     { "name": "ThrottleTimeMs", "type": "int32", "versions": "2+", "ignorable": true,
diff --git a/clients/src/test/java/org/apache/kafka/common/requests/JoinGroupRequestTest.java b/clients/src/test/java/org/apache/kafka/common/requests/JoinGroupRequestTest.java
index 3de00b8d467..c70b7eda5da 100644
--- a/clients/src/test/java/org/apache/kafka/common/requests/JoinGroupRequestTest.java
+++ b/clients/src/test/java/org/apache/kafka/common/requests/JoinGroupRequestTest.java
@@ -19,12 +19,14 @@ package org.apache.kafka.common.requests;
 import org.apache.kafka.common.errors.InvalidConfigurationException;
 import org.apache.kafka.common.errors.UnsupportedVersionException;
 import org.apache.kafka.common.message.JoinGroupRequestData;
+import org.apache.kafka.common.protocol.MessageUtil;
 import org.apache.kafka.test.TestUtils;
 
 import org.junit.jupiter.api.Test;
 
 import java.util.Arrays;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 public class JoinGroupRequestTest {
@@ -61,4 +63,20 @@ public class JoinGroupRequestTest {
                 .setProtocolType("consumer")
         ).build((short) 4));
     }
+
+    @Test
+    public void testRebalanceTimeoutDefaultsToSessionTimeoutV0() {
+        int sessionTimeoutMs = 30000;
+        short version = 0;
+
+        var buffer = MessageUtil.toByteBufferAccessor(new JoinGroupRequestData()
+                .setGroupId("groupId")
+                .setMemberId("consumerId")
+                .setProtocolType("consumer")
+                .setSessionTimeoutMs(sessionTimeoutMs), version);
+
+        JoinGroupRequest request = JoinGroupRequest.parse(buffer, version);
+        assertEquals(sessionTimeoutMs, request.data().sessionTimeoutMs());
+        assertEquals(sessionTimeoutMs, request.data().rebalanceTimeoutMs());
+    }
 }
diff --git a/clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java b/clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
index c839d68b986..ffb95673e55 100644
--- a/clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
+++ b/clients/src/test/java/org/apache/kafka/common/requests/RequestResponseTest.java
@@ -728,6 +728,14 @@ public class RequestResponseTest {
         assertEquals(request.isolationLevel(), deserialized.isolationLevel());
     }
 
+    @Test
+    public void testJoinGroupRequestV0RebalanceTimeout() {
+        final short version = 0;
+        JoinGroupRequest jgr = createJoinGroupRequest(version);
+        JoinGroupRequest jgr2 = JoinGroupRequest.parse(jgr.serialize(), version);
+        assertEquals(jgr2.data().rebalanceTimeoutMs(), jgr.data().rebalanceTimeoutMs());
+    }
+
     @Test
     public void testSerializeWithHeader() {
         CreatableTopicCollection topicsToCreate = new CreatableTopicCollection(1);