public class MemberDescription {
    private final String memberId;
    private final Optional<String> groupInstanceId;
    private final String clientId;
    private final String host;
    private final MemberAssignment assignment;
    private final Optional<MemberAssignment> targetAssignment;
    private final Optional<Integer> memberEpoch;
    private final Boolean isClassic; Optional<Boolean> upgraded;

	public MemberDescription(String memberId,
                             Optional<String> groupInstanceId,
                             String clientId,
                             String host,
                             MemberAssignment assignment,
                             Optional<MemberAssignment> targetAssignment,
                             Optional<Integer> memberEpoch,
                             Optional<Boolean> upgraded
    ) {
        this.memberId = memberId == null ? "" : memberId;
        this.groupInstanceId = groupInstanceId;
        this.clientId = clientId == null ? "" : clientId;
        this.host = host == null ? "" : host;
        this.assignment = assignment == null ?
            new MemberAssignment(Collections.emptySet()) : assignment;
        this.targetAssignment = targetAssignment;
        this.memberEpoch = memberEpoch;
        this.upgraded = upgraded;
    }

    /**
     * @deprecated Since 4.0. Use {@link #MemberDescription(String, Optional, String, String, MemberAssignment, Optional, Optional, Optional)}.
     */
    @Deprecated
    public MemberDescription(String memberId,
                             Optional<String> groupInstanceId,
                             String clientId,
                             String host,
                             MemberAssignment assignment,
                             Optional<MemberAssignment> targetAssignment
    ) {
        this(
            memberId,
            groupInstanceId,
            clientId,
            host,
            assignment,
            targetAssignment,
            Optional.empty(),
            Optional.empty()
        );
    }

    /**
     * @deprecated Since 4.0. Use {@link #MemberDescription(String, Optional, String, String, MemberAssignment, Optional, Optional, Optional)}.
     */
    @Deprecated
    public MemberDescription(
        String memberId,
        Optional<String> groupInstanceId,
        String clientId,
        String host,
        MemberAssignment assignment
    ) {
        this(
            memberId,
            groupInstanceId,
            clientId,
            host,
            assignment,
            Optional.empty()
        );
    }

    /**
     * @deprecated Since 4.0. Use {@link #MemberDescription(String, Optional, String, String, MemberAssignment, Optional, Optional, Optional)}.
     */
    @Deprecated
    public MemberDescription(String memberId,
                             String clientId,
                             String host,
                             MemberAssignment assignment) {
        this(memberId, Optional.empty(), clientId, host, assignment);
    }

	// ...

	/**
	 * The epoch of the group member.
	 */
	public Optional<Integer> memberEpoch() {
		return memberEpoch;
	}

    /**
     * The flag indicating whether a member is classic.
     */
    public BooleanOptional<Boolean> isClassicupgraded() {
        return isClassicupgraded;
    }
}

{
  "apiKey": 69,
  "type": "response",
  "name": "ConsumerGroupDescribeResponse",
  "validVersions": "0-1",  <-- bump to 0-1
  "flexibleVersions": "0+",
  // Supported errors:
  // - GROUP_AUTHORIZATION_FAILED (version 0+)
  // - NOT_COORDINATOR (version 0+)
  // - COORDINATOR_NOT_AVAILABLE (version 0+)
  // - COORDINATOR_LOAD_IN_PROGRESS (version 0+)
  // - INVALID_REQUEST (version 0+)
  // - INVALID_GROUP_ID (version 0+)
  // - GROUP_ID_NOT_FOUND (version 0+)
  "fields": [
    { "name": "ThrottleTimeMs", "type": "int32", "versions": "0+",
      "about": "The duration in milliseconds for which the request was throttled due to a quota violation, or zero if the request did not violate any quota." },
    { "name": "Groups", "type": "[]DescribedGroup", "versions": "0+",
      "about": "Each described group.",
      "fields": [
        { "name": "ErrorCode", "type": "int16", "versions": "0+",
          "about": "The describe error, or 0 if there was no error." },
        { "name": "ErrorMessage", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
          "about": "The top-level error message, or null if there was no error." },
        { "name": "GroupId", "type": "string", "versions": "0+", "entityType": "groupId",
          "about": "The group ID string." },
        { "name": "GroupState", "type": "string", "versions": "0+",
          "about": "The group state string, or the empty string." },
        { "name": "GroupEpoch", "type": "int32", "versions": "0+",
          "about": "The group epoch." },
        { "name": "AssignmentEpoch", "type": "int32", "versions": "0+",
          "about": "The assignment epoch." },
        { "name": "AssignorName", "type": "string", "versions": "0+",
          "about": "The selected assignor." },
        { "name": "Members", "type": "[]Member", "versions": "0+",
          "about": "The members.",
          "fields": [
            { "name": "MemberId", "type": "string", "versions": "0+",
              "about": "The member ID." },
            { "name": "InstanceId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "The member instance ID." },
            { "name": "RackId", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "The member rack ID." },
            { "name": "MemberEpoch", "type": "int32", "versions": "0+",
              "about": "The current member epoch." },
            { "name": "ClientId", "type": "string", "versions": "0+",
              "about": "The client ID." },
            { "name": "ClientHost", "type": "string", "versions": "0+",
              "about": "The client host." },
            { "name": "SubscribedTopicNames", "type": "[]string", "versions": "0+", "entityType": "topicName",
              "about": "The subscribed topic names." },
            { "name": "SubscribedTopicRegex", "type": "string", "versions": "0+", "nullableVersions": "0+", "default": "null",
              "about": "the subscribed topic regex otherwise or null of not provided." },
            { "name": "Assignment", "type": "Assignment", "versions": "0+",
              "about": "The current assignment." },
            { "name": "TargetAssignment", "type": "Assignment", "versions": "0+",
              "about": "The target assignment." },
            { "name": "IsClassicMemberType", "type": "boolint8", "versions": "1+", "default": "-1", "ignorable": true,
              "about": "True-1 for unknown. 0 for classic member. +1 for consumer member." }  <-- new field
          ]},
        { "name": "AuthorizedOperations", "type": "int32", "versions": "0+", "default": "-2147483648",
          "about": "32-bit bitfield to represent authorized operations for this group." }
      ]
    }
  ],
  "commonStructs": [
    { "name": "TopicPartitions", "versions": "0+", "fields": [
      { "name": "TopicId", "type": "uuid", "versions": "0+",
        "about": "The topic ID." },
      { "name": "TopicName", "type": "string", "versions": "0+", "entityType": "topicName",
        "about": "The topic name." },
      { "name": "Partitions", "type": "[]int32", "versions": "0+",
        "about": "The partitions." }
    ]},
    { "name": "Assignment", "versions": "0+", "fields": [
      { "name": "TopicPartitions", "type": "[]TopicPartitions", "versions": "0+",
        "about": "The assigned topic-partitions to the member." }
    ]}
  ]
}