diff --git a/docs/reference/cluster/state.asciidoc b/docs/reference/cluster/state.asciidoc
index d0ff3290c74..a20ff04d83f 100644
--- a/docs/reference/cluster/state.asciidoc
+++ b/docs/reference/cluster/state.asciidoc
@@ -15,6 +15,12 @@ of the cluster state (its size when serialized for transmission over
 the network), and the cluster state itself, which can be filtered to
 only retrieve the parts of interest, as described below.
 
+The cluster's `cluster_uuid` is also returned as part of the top-level
+response, in addition to the `metadata` section. added[6.4.0]
+
+NOTE: While the cluster is still forming, it is possible for the `cluster_uuid`
+      to be `_na_` as well as the cluster state's version to be `-1`.
+
 By default, the cluster state request is routed to the master node, to
 ensure that the latest cluster state is returned.   
 For debugging purposes, you can retrieve the cluster state local to a
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/10_basic.yml b/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/10_basic.yml
index e3af21412ca..c38a33fdff1 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/10_basic.yml
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/10_basic.yml
@@ -2,7 +2,7 @@
 "get cluster state":
   - do:
       cluster.state: {}
-  
+
   - is_true: master_node
 
 ---
@@ -18,3 +18,18 @@
   - is_true: master_node
   - gte: { compressed_size_in_bytes: 50 }
   - is_true: compressed_size
+
+---
+"get cluster state returns cluster_uuid at the top level":
+  - skip:
+      version:  " - 6.99.99"
+      reason:   "cluster state including cluster_uuid at the top level is new in v6.4.0 and higher"
+
+  - do:
+      cluster.state:
+        human: true
+
+  - is_true: cluster_uuid
+  - is_true: master_node
+  - gte: { compressed_size_in_bytes: 50 }
+  - is_true: compressed_size
diff --git a/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/20_filtering.yml b/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/20_filtering.yml
index 1e1d5712560..f9e5a0c03df 100644
--- a/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/20_filtering.yml
+++ b/rest-api-spec/src/main/resources/rest-api-spec/test/cluster.state/20_filtering.yml
@@ -156,3 +156,19 @@ setup:
   - is_true: routing_table.indices.index1
   - is_true: metadata.indices.index2
   - is_true: routing_table.indices.index2
+
+---
+"Filtering the cluster state returns cluster_uuid at the top level regardless of metric filters":
+  - skip:
+      version:  " - 6.99.99"
+      reason:   "cluster state including cluster_uuid at the top level is new in v6.4.0 and higher"
+
+  - do:
+      cluster.state:
+        metric: [ master_node, version, metadata ]
+
+  - is_true: cluster_uuid
+  - is_true: master_node
+  - is_true: version
+  - is_true: state_uuid
+  - is_true: metadata
diff --git a/server/src/main/java/org/elasticsearch/cluster/ClusterState.java b/server/src/main/java/org/elasticsearch/cluster/ClusterState.java
index 30c8df07ec1..2b991d1dc61 100644
--- a/server/src/main/java/org/elasticsearch/cluster/ClusterState.java
+++ b/server/src/main/java/org/elasticsearch/cluster/ClusterState.java
@@ -326,6 +326,9 @@ public class ClusterState implements ToXContentFragment, Diffable<ClusterState>
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
         EnumSet<Metric> metrics = Metric.parseString(params.param("metric", "_all"), true);
 
+        // always provide the cluster_uuid as part of the top-level response (also part of the metadata response)
+        builder.field("cluster_uuid", metaData().clusterUUID());
+
         if (metrics.contains(Metric.VERSION)) {
             builder.field("version", version);
             builder.field("state_uuid", stateUUID);
diff --git a/server/src/test/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponseTests.java b/server/src/test/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponseTests.java
index 4ced505717a..7d671096514 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponseTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/cluster/reroute/ClusterRerouteResponseTests.java
@@ -69,6 +69,7 @@ public class ClusterRerouteResponseTests extends ESTestCase {
             assertEquals("{\n" +
                     "  \"acknowledged\" : true,\n" +
                     "  \"state\" : {\n" +
+                    "    \"cluster_uuid\" : \"_na_\",\n" +
                     "    \"version\" : 0,\n" +
                     "    \"state_uuid\" : \"" + clusterState.stateUUID() + "\",\n" +
                     "    \"master_node\" : \"node0\",\n" +
@@ -136,6 +137,7 @@ public class ClusterRerouteResponseTests extends ESTestCase {
             assertEquals("{\n" +
                     "  \"acknowledged\" : true,\n" +
                     "  \"state\" : {\n" +
+                    "    \"cluster_uuid\" : \"_na_\",\n" +
                     "    \"version\" : 0,\n" +
                     "    \"state_uuid\" : \"" + clusterState.stateUUID() + "\",\n" +
                     "    \"master_node\" : \"node0\"\n" +
@@ -168,6 +170,7 @@ public class ClusterRerouteResponseTests extends ESTestCase {
             assertEquals("{\n" +
                     "  \"acknowledged\" : true,\n" +
                     "  \"state\" : {\n" +
+                    "    \"cluster_uuid\" : \"_na_\",\n" +
                     "    \"metadata\" : {\n" +
                     "      \"cluster_uuid\" : \"_na_\",\n" +
                     "      \"templates\" : { },\n" +
diff --git a/x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDocTests.java b/x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDocTests.java
index 4a096f0ca4a..098f4190b0e 100644
--- a/x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDocTests.java
+++ b/x-pack/plugin/monitoring/src/test/java/org/elasticsearch/xpack/monitoring/collector/cluster/ClusterStatsMonitoringDocTests.java
@@ -17,6 +17,7 @@ import org.elasticsearch.action.admin.indices.stats.ShardStats;
 import org.elasticsearch.cluster.ClusterName;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.health.ClusterHealthStatus;
+import org.elasticsearch.cluster.metadata.MetaData;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.ShardRouting;
@@ -188,6 +189,7 @@ public class ClusterStatsMonitoringDocTests extends BaseMonitoringDocTestCase<Cl
 
     @Override
     public void testToXContent() throws IOException {
+        final String clusterUuid = "_cluster";
         final ClusterName clusterName = new ClusterName("_cluster_name");
         final TransportAddress transportAddress = new TransportAddress(TransportAddress.META_ADDRESS, 9300);
         final DiscoveryNode discoveryNode = new DiscoveryNode("_node_name",
@@ -201,6 +203,7 @@ public class ClusterStatsMonitoringDocTests extends BaseMonitoringDocTestCase<Cl
                                                                 Version.V_6_0_0_beta1);
 
         final ClusterState clusterState = ClusterState.builder(clusterName)
+                                                        .metaData(MetaData.builder().clusterUUID(clusterUuid).build())
                                                         .stateUUID("_state_uuid")
                                                         .version(12L)
                                                         .nodes(DiscoveryNodes.builder()
@@ -500,6 +503,7 @@ public class ClusterStatsMonitoringDocTests extends BaseMonitoringDocTestCase<Cl
                   + "\"cluster_state\":{"
                     + "\"nodes_hash\":1314980060,"
                     + "\"status\":\"green\","
+                    + "\"cluster_uuid\":\"_cluster\","
                     + "\"version\":12,"
                     + "\"state_uuid\":\"_state_uuid\","
                     + "\"master_node\":\"_node\","