diff --git a/qa/full-cluster-restart/src/test/java/org/elasticsearch/upgrades/FullClusterRestartIT.java b/qa/full-cluster-restart/src/test/java/org/elasticsearch/upgrades/FullClusterRestartIT.java
index 190523a3bc7c6..eb7078b2b189c 100644
--- a/qa/full-cluster-restart/src/test/java/org/elasticsearch/upgrades/FullClusterRestartIT.java
+++ b/qa/full-cluster-restart/src/test/java/org/elasticsearch/upgrades/FullClusterRestartIT.java
@@ -917,7 +917,7 @@ public void testSoftDeletes() throws Exception {
                 mappingsAndSettings.startObject("settings");
                 mappingsAndSettings.field("number_of_shards", 1);
                 mappingsAndSettings.field("number_of_replicas", 1);
-                if (getOldClusterVersion().onOrAfter(Version.V_6_5_0) && randomBoolean()) {
+                if (randomBoolean()) {
                     mappingsAndSettings.field("soft_deletes.enabled", true);
                 }
                 mappingsAndSettings.endObject();
diff --git a/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/RecoveryIT.java b/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/RecoveryIT.java
index 49bd5bb3585b6..602a31288ef46 100644
--- a/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/RecoveryIT.java
+++ b/qa/rolling-upgrade/src/test/java/org/elasticsearch/upgrades/RecoveryIT.java
@@ -356,7 +356,7 @@ public void testRecoveryWithSoftDeletes() throws Exception {
                 // before timing out
                 .put(INDEX_DELAYED_NODE_LEFT_TIMEOUT_SETTING.getKey(), "100ms")
                 .put(SETTING_ALLOCATION_MAX_RETRY.getKey(), "0"); // fail faster
-            if (getNodeId(v -> v.onOrAfter(Version.V_6_5_0)) != null && randomBoolean()) {
+            if (randomBoolean()) {
                 settings.put(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), true);
             }
             createIndex(index, settings.build());
diff --git a/server/src/main/java/org/elasticsearch/Version.java b/server/src/main/java/org/elasticsearch/Version.java
index 844b963e9aa83..ec79c17a834f1 100644
--- a/server/src/main/java/org/elasticsearch/Version.java
+++ b/server/src/main/java/org/elasticsearch/Version.java
@@ -46,22 +46,6 @@ public class Version implements Comparable<Version>, ToXContentFragment {
      */
     public static final int V_EMPTY_ID = 0;
     public static final Version V_EMPTY = new Version(V_EMPTY_ID, org.apache.lucene.util.Version.LATEST);
-    public static final int V_6_5_0_ID = 6050099;
-    public static final Version V_6_5_0 = new Version(V_6_5_0_ID, org.apache.lucene.util.Version.LUCENE_7_5_0);
-    public static final int V_6_5_1_ID = 6050199;
-    public static final Version V_6_5_1 = new Version(V_6_5_1_ID, org.apache.lucene.util.Version.LUCENE_7_5_0);
-    public static final int V_6_5_2_ID = 6050299;
-    public static final Version V_6_5_2 = new Version(V_6_5_2_ID, org.apache.lucene.util.Version.LUCENE_7_5_0);
-    public static final int V_6_5_3_ID = 6050399;
-    public static final Version V_6_5_3 = new Version(V_6_5_3_ID, org.apache.lucene.util.Version.LUCENE_7_5_0);
-    public static final int V_6_5_4_ID = 6050499;
-    public static final Version V_6_5_4 = new Version(V_6_5_4_ID, org.apache.lucene.util.Version.LUCENE_7_5_0);
-    public static final int V_6_6_0_ID = 6060099;
-    public static final Version V_6_6_0 = new Version(V_6_6_0_ID, org.apache.lucene.util.Version.LUCENE_7_6_0);
-    public static final int V_6_6_1_ID = 6060199;
-    public static final Version V_6_6_1 = new Version(V_6_6_1_ID, org.apache.lucene.util.Version.LUCENE_7_6_0);
-    public static final int V_6_6_2_ID = 6060299;
-    public static final Version V_6_6_2 = new Version(V_6_6_2_ID, org.apache.lucene.util.Version.LUCENE_7_6_0);
     public static final int V_6_8_0_ID = 6080099;
     public static final Version V_6_8_0 = new Version(V_6_8_0_ID, org.apache.lucene.util.Version.LUCENE_7_7_0);
     public static final int V_6_8_1_ID = 6080199;
@@ -116,22 +100,6 @@ public static Version fromId(int id) {
                 return V_6_8_1;
             case V_6_8_0_ID:
                 return V_6_8_0;
-            case V_6_6_2_ID:
-                return V_6_6_2;
-            case V_6_6_1_ID:
-                return V_6_6_1;
-            case V_6_6_0_ID:
-                return V_6_6_0;
-            case V_6_5_4_ID:
-                return V_6_5_4;
-            case V_6_5_3_ID:
-                return V_6_5_3;
-            case V_6_5_2_ID:
-                return V_6_5_2;
-            case V_6_5_1_ID:
-                return V_6_5_1;
-            case V_6_5_0_ID:
-                return V_6_5_0;
             case V_EMPTY_ID:
                 return V_EMPTY;
             default:
diff --git a/server/src/main/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelper.java b/server/src/main/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelper.java
index a707a9ae980b7..b5bae4bc3f0d4 100644
--- a/server/src/main/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelper.java
+++ b/server/src/main/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelper.java
@@ -20,7 +20,6 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.coordination.CoordinationMetaData.VotingConfiguration;
 import org.elasticsearch.cluster.coordination.CoordinationState.VoteCollection;
@@ -150,8 +149,6 @@ String getDescription() {
 
             if (clusterState.getLastAcceptedConfiguration().isEmpty()) {
 
-                // TODO handle the case that there is a 6.x node around here, when rolling upgrades are supported
-
                 final String bootstrappingDescription;
 
                 if (INITIAL_MASTER_NODES_SETTING.get(Settings.EMPTY).equals(INITIAL_MASTER_NODES_SETTING.get(settings))) {
@@ -164,8 +161,8 @@ String getDescription() {
                 }
 
                 return String.format(Locale.ROOT,
-                    "master not discovered yet, this node has not previously joined a bootstrapped (v%d+) cluster, and %s: %s",
-                    Version.V_6_6_0.major + 1, bootstrappingDescription, discoveryStateIgnoringQuorum);
+                    "master not discovered yet, this node has not previously joined a bootstrapped cluster, and %s: %s",
+                    bootstrappingDescription, discoveryStateIgnoringQuorum);
             }
 
             assert clusterState.getLastCommittedConfiguration().isEmpty() == false;
diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java b/server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java
index 412e16e14a3a5..3598753f80d9c 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/IndexMetaData.java
@@ -1408,10 +1408,10 @@ public static IndexMetaData fromXContent(XContentParser parser) throws IOExcepti
                     throw new IllegalArgumentException("Unexpected token " + token);
                 }
             }
-            if (Assertions.ENABLED && Version.indexCreated(builder.settings).onOrAfter(Version.V_6_5_0)) {
+            if (Assertions.ENABLED) {
                 assert mappingVersion : "mapping version should be present for indices created on or after 6.5.0";
             }
-            if (Assertions.ENABLED && Version.indexCreated(builder.settings).onOrAfter(Version.V_6_5_0)) {
+            if (Assertions.ENABLED) {
                 assert settingsVersion : "settings version should be present for indices created on or after 6.5.0";
             }
             if (Assertions.ENABLED && Version.indexCreated(builder.settings).onOrAfter(Version.V_7_2_0)) {
diff --git a/server/src/main/java/org/elasticsearch/index/IndexService.java b/server/src/main/java/org/elasticsearch/index/IndexService.java
index a7751bc765552..c186a725c82c1 100644
--- a/server/src/main/java/org/elasticsearch/index/IndexService.java
+++ b/server/src/main/java/org/elasticsearch/index/IndexService.java
@@ -26,7 +26,6 @@
 import org.apache.lucene.store.Directory;
 import org.apache.lucene.util.Accountable;
 import org.elasticsearch.Assertions;
-import org.elasticsearch.Version;
 import org.elasticsearch.client.Client;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.routing.ShardRouting;
@@ -660,9 +659,7 @@ public IndexMetaData getMetaData() {
     public synchronized void updateMetaData(final IndexMetaData currentIndexMetaData, final IndexMetaData newIndexMetaData) {
         final boolean updateIndexMetaData = indexSettings.updateIndexMetaData(newIndexMetaData);
 
-        if (Assertions.ENABLED
-                && currentIndexMetaData != null
-                && currentIndexMetaData.getCreationVersion().onOrAfter(Version.V_6_5_0)) {
+        if (Assertions.ENABLED && currentIndexMetaData != null) {
             final long currentSettingsVersion = currentIndexMetaData.getSettingsVersion();
             final long newSettingsVersion = newIndexMetaData.getSettingsVersion();
             if (currentSettingsVersion == newSettingsVersion) {
diff --git a/server/src/main/java/org/elasticsearch/index/IndexSettings.java b/server/src/main/java/org/elasticsearch/index/IndexSettings.java
index d4cc38f0b959c..ebcf362b1c9e4 100644
--- a/server/src/main/java/org/elasticsearch/index/IndexSettings.java
+++ b/server/src/main/java/org/elasticsearch/index/IndexSettings.java
@@ -458,7 +458,7 @@ public IndexSettings(final IndexMetaData indexMetaData, final Settings nodeSetti
         generationThresholdSize = scopedSettings.get(INDEX_TRANSLOG_GENERATION_THRESHOLD_SIZE_SETTING);
         mergeSchedulerConfig = new MergeSchedulerConfig(this);
         gcDeletesInMillis = scopedSettings.get(INDEX_GC_DELETES_SETTING).getMillis();
-        softDeleteEnabled = version.onOrAfter(Version.V_6_5_0) && scopedSettings.get(INDEX_SOFT_DELETES_SETTING);
+        softDeleteEnabled = scopedSettings.get(INDEX_SOFT_DELETES_SETTING);
         softDeleteRetentionOperations = scopedSettings.get(INDEX_SOFT_DELETES_RETENTION_OPERATIONS_SETTING);
         retentionLeaseMillis = scopedSettings.get(INDEX_SOFT_DELETES_RETENTION_LEASE_PERIOD_SETTING).millis();
         warmerEnabled = scopedSettings.get(INDEX_WARMER_ENABLED_SETTING);
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/BaseGeoShapeFieldMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/BaseGeoShapeFieldMapper.java
index 74892bf7d516c..20151f301d791 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/BaseGeoShapeFieldMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/BaseGeoShapeFieldMapper.java
@@ -190,7 +190,7 @@ public Mapper.Builder parse(String name, Map<String, Object> node, ParserContext
                 }
             }
             final Builder builder;
-            if (parsedDeprecatedParams || parserContext.indexVersionCreated().before(Version.V_6_6_0)) {
+            if (parsedDeprecatedParams) {
                 // Legacy index-based shape
                 builder = new LegacyGeoShapeFieldMapper.Builder(name, deprecatedParameters);
             } else {
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/LegacyGeoShapeFieldMapper.java b/server/src/main/java/org/elasticsearch/index/mapper/LegacyGeoShapeFieldMapper.java
index 9c8726a498a3c..c4996eab901dd 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/LegacyGeoShapeFieldMapper.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/LegacyGeoShapeFieldMapper.java
@@ -208,8 +208,6 @@ private void setupFieldTypeDeprecatedParameters(BuilderContext context) {
             }
             if (deprecatedParameters.tree != null) {
                 ft.setTree(deprecatedParameters.tree);
-            } else if (context.indexCreatedVersion().before(Version.V_6_6_0)) {
-                ft.setTree(DeprecatedParameters.PrefixTrees.GEOHASH);
             }
             if (deprecatedParameters.treeLevels != null) {
                 ft.setTreeLevels(deprecatedParameters.treeLevels);
@@ -527,8 +525,7 @@ protected void doXContentBody(XContentBuilder builder, boolean includeDefaults,
         super.doXContentBody(builder, includeDefaults, params);
 
         if (includeDefaults
-            || (fieldType().tree().equals(indexCreatedVersion.onOrAfter(Version.V_6_6_0) ?
-                    DeprecatedParameters.Defaults.TREE : DeprecatedParameters.PrefixTrees.GEOHASH)) == false) {
+            || (fieldType().tree().equals(DeprecatedParameters.Defaults.TREE)) == false) {
             builder.field(DeprecatedParameters.Names.TREE.getPreferredName(), fieldType().tree());
         }
 
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java b/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
index 487a6ac4789e3..fc33dcafc63b6 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/MapperService.java
@@ -260,9 +260,7 @@ private void assertMappingVersion(
             final IndexMetaData currentIndexMetaData,
             final IndexMetaData newIndexMetaData,
             final Map<String, DocumentMapper> updatedEntries) {
-        if (Assertions.ENABLED
-                && currentIndexMetaData != null
-                && currentIndexMetaData.getCreationVersion().onOrAfter(Version.V_6_5_0)) {
+        if (Assertions.ENABLED && currentIndexMetaData != null) {
             if (currentIndexMetaData.getMappingVersion() == newIndexMetaData.getMappingVersion()) {
                 // if the mapping version is unchanged, then there should not be any updates and all mappings should be the same
                 assert updatedEntries.isEmpty() : updatedEntries;
diff --git a/server/src/main/java/org/elasticsearch/index/mapper/ParseContext.java b/server/src/main/java/org/elasticsearch/index/mapper/ParseContext.java
index 4cfd5be2afed3..b2c536a900e33 100644
--- a/server/src/main/java/org/elasticsearch/index/mapper/ParseContext.java
+++ b/server/src/main/java/org/elasticsearch/index/mapper/ParseContext.java
@@ -24,7 +24,6 @@
 import org.apache.lucene.document.Field;
 import org.apache.lucene.index.IndexableField;
 import org.apache.lucene.util.BytesRef;
-import org.elasticsearch.Version;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.index.IndexSettings;
 
@@ -458,18 +457,10 @@ public Iterable<Document> nonRootDocuments() {
         void postParse() {
             if (documents.size() > 1) {
                 docsReversed = true;
-                if (indexSettings.getIndexVersionCreated().onOrAfter(Version.V_6_5_0)) {
-                    /**
-                     * For indices created on or after {@link Version#V_6_5_0} we preserve the order
-                     * of the children while ensuring that parents appear after them.
-                     */
-                    List<Document> newDocs = reorderParent(documents);
-                    documents.clear();
-                    documents.addAll(newDocs);
-                } else {
-                    // reverse the order of docs for nested docs support, parent should be last
-                    Collections.reverse(documents);
-                }
+                // We preserve the order of the children while ensuring that parents appear after them.
+                List<Document> newDocs = reorderParent(documents);
+                documents.clear();
+                documents.addAll(newDocs);
             }
         }
 
diff --git a/server/src/main/java/org/elasticsearch/index/similarity/SimilarityService.java b/server/src/main/java/org/elasticsearch/index/similarity/SimilarityService.java
index 57cbc961aacc0..3fe20a1f3b26e 100644
--- a/server/src/main/java/org/elasticsearch/index/similarity/SimilarityService.java
+++ b/server/src/main/java/org/elasticsearch/index/similarity/SimilarityService.java
@@ -212,9 +212,8 @@ private static void validateScoresArePositive(Version indexCreatedVersion, Simil
         for (int freq = 1; freq <= 10; ++freq) {
             float score = scorer.score(freq, norm);
             if (score < 0) {
-                fail(indexCreatedVersion, "Similarities should not return negative scores:\n" +
-                        scorer.explain(Explanation.match(freq, "term freq"), norm));
-                break;
+                throw new IllegalArgumentException("Similarities should not return negative scores:\n" +
+                    scorer.explain(Explanation.match(freq, "term freq"), norm));
             }
         }
     }
@@ -230,10 +229,9 @@ private static void validateScoresDoNotDecreaseWithFreq(Version indexCreatedVers
         for (int freq = 1; freq <= 10; ++freq) {
             float score = scorer.score(freq, norm);
             if (score < previousScore) {
-                fail(indexCreatedVersion, "Similarity scores should not decrease when term frequency increases:\n" +
-                        scorer.explain(Explanation.match(freq - 1, "term freq"), norm) + "\n" +
-                        scorer.explain(Explanation.match(freq, "term freq"), norm));
-                break;
+                throw new IllegalArgumentException("Similarity scores should not decrease when term frequency increases:\n" +
+                    scorer.explain(Explanation.match(freq - 1, "term freq"), norm) + "\n" +
+                    scorer.explain(Explanation.match(freq, "term freq"), norm));
             }
             previousScore = score;
         }
@@ -256,22 +254,12 @@ private static void validateScoresDoNotIncreaseWithNorm(Version indexCreatedVers
             }
             float score = scorer.score(1, norm);
             if (score > previousScore) {
-                fail(indexCreatedVersion, "Similarity scores should not increase when norm increases:\n" +
-                        scorer.explain(Explanation.match(1, "term freq"), norm - 1) + "\n" +
-                        scorer.explain(Explanation.match(1, "term freq"), norm));
-                break;
+                throw new IllegalArgumentException("Similarity scores should not increase when norm increases:\n" +
+                    scorer.explain(Explanation.match(1, "term freq"), norm - 1) + "\n" +
+                    scorer.explain(Explanation.match(1, "term freq"), norm));
             }
             previousScore = score;
             previousNorm = norm;
         }
     }
-
-    private static void fail(Version indexCreatedVersion, String message) {
-        if (indexCreatedVersion.onOrAfter(Version.V_7_0_0)) {
-            throw new IllegalArgumentException(message);
-        } else if (indexCreatedVersion.onOrAfter(Version.V_6_5_0)) {
-            deprecationLogger.deprecated(message);
-        }
-    }
-
 }
diff --git a/server/src/main/java/org/elasticsearch/search/fetch/FetchPhase.java b/server/src/main/java/org/elasticsearch/search/fetch/FetchPhase.java
index c23be0f4cb994..196e74e0bbabd 100644
--- a/server/src/main/java/org/elasticsearch/search/fetch/FetchPhase.java
+++ b/server/src/main/java/org/elasticsearch/search/fetch/FetchPhase.java
@@ -31,7 +31,6 @@
 import org.apache.lucene.search.Weight;
 import org.apache.lucene.util.BitSet;
 import org.elasticsearch.ExceptionsHelper;
-import org.elasticsearch.Version;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.document.DocumentField;
@@ -383,32 +382,19 @@ private SearchHit.NestedIdentity getInternalNestedIdentity(SearchContext context
             BitSet parentBits = context.bitsetFilterCache().getBitSetProducer(parentFilter).getBitSet(subReaderContext);
 
             int offset = 0;
-            if (indexSettings.getIndexVersionCreated().onOrAfter(Version.V_6_5_0)) {
-                /**
-                 * Starts from the previous parent and finds the offset of the
-                 * <code>nestedSubDocID</code> within the nested children. Nested documents
-                 * are indexed in the same order than in the source array so the offset
-                 * of the nested child is the number of nested document with the same parent
-                 * that appear before him.
-                 */
-                int previousParent = parentBits.prevSetBit(currentParent);
-                for (int docId = childIter.advance(previousParent + 1); docId < nestedSubDocId && docId != DocIdSetIterator.NO_MORE_DOCS;
-                        docId = childIter.nextDoc()) {
-                    offset++;
-                }
-                currentParent = nestedSubDocId;
-            } else {
-                /**
-                 * Nested documents are in reverse order in this version so we start from the current nested document
-                 * and find the number of documents with the same parent that appear after it.
-                 */
-                int nextParent = parentBits.nextSetBit(currentParent);
-                for (int docId = childIter.advance(currentParent + 1); docId < nextParent && docId != DocIdSetIterator.NO_MORE_DOCS;
-                        docId = childIter.nextDoc()) {
-                    offset++;
-                }
-                currentParent = nextParent;
+            /**
+             * Starts from the previous parent and finds the offset of the
+             * <code>nestedSubDocID</code> within the nested children. Nested documents
+             * are indexed in the same order than in the source array so the offset
+             * of the nested child is the number of nested document with the same parent
+             * that appear before him.
+             */
+            int previousParent = parentBits.prevSetBit(currentParent);
+            for (int docId = childIter.advance(previousParent + 1); docId < nestedSubDocId && docId != DocIdSetIterator.NO_MORE_DOCS;
+                 docId = childIter.nextDoc()) {
+                offset++;
             }
+            currentParent = nestedSubDocId;
             current = nestedObjectMapper = nestedParentObjectMapper;
             int currentPrefix = current == null ? 0 : current.name().length() + 1;
             nestedIdentity = new SearchHit.NestedIdentity(originalName.substring(currentPrefix), offset, nestedIdentity);
diff --git a/server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java b/server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java
index 8abd4b9f40d5c..6598d32bc2ca8 100644
--- a/server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java
@@ -397,10 +397,6 @@ public SortFieldAndFormat build(QueryShardContext context) throws IOException {
             Nested nested = null;
             if (isUnmapped == false) {
                 if (nestedSort != null) {
-                    if (context.indexVersionCreated().before(Version.V_6_5_0) && nestedSort.getMaxChildren() != Integer.MAX_VALUE) {
-                        throw new QueryShardException(context,
-                            "max_children is only supported on v6.5.0 or higher");
-                    }
                     if (nestedSort.getNestedSort() != null && nestedSort.getMaxChildren() != Integer.MAX_VALUE) {
                         throw new QueryShardException(context,
                             "max_children is only supported on last level of nested sort");
diff --git a/server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java b/server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java
index 116a54a71103b..73877b3faa309 100644
--- a/server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java
@@ -28,7 +28,6 @@
 import org.apache.lucene.search.SortField;
 import org.apache.lucene.util.BitSet;
 import org.elasticsearch.ElasticsearchParseException;
-import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.geo.GeoDistance;
@@ -613,10 +612,6 @@ public SortFieldAndFormat build(QueryShardContext context) throws IOException {
 
         final Nested nested;
         if (nestedSort != null) {
-            if (context.indexVersionCreated().before(Version.V_6_5_0) && nestedSort.getMaxChildren() != Integer.MAX_VALUE) {
-                throw new QueryShardException(context,
-                    "max_children is only supported on v6.5.0 or higher");
-            }
             if (nestedSort.getNestedSort() != null && nestedSort.getMaxChildren() != Integer.MAX_VALUE)  {
                 throw new QueryShardException(context,
                     "max_children is only supported on last level of nested sort");
diff --git a/server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java b/server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java
index d858f0f7c6ac3..21de011e276b7 100644
--- a/server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java
@@ -26,7 +26,6 @@
 import org.apache.lucene.search.SortField;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.BytesRefBuilder;
-import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -312,10 +311,6 @@ public SortFieldAndFormat build(QueryShardContext context) throws IOException {
 
         final Nested nested;
         if (nestedSort != null) {
-            if (context.indexVersionCreated().before(Version.V_6_5_0) && nestedSort.getMaxChildren() != Integer.MAX_VALUE) {
-                throw new QueryShardException(context,
-                    "max_children is only supported on v6.5.0 or higher");
-            }
             if (nestedSort.getNestedSort() != null && nestedSort.getMaxChildren() != Integer.MAX_VALUE)  {
                 throw new QueryShardException(context,
                     "max_children is only supported on last level of nested sort");
diff --git a/server/src/test/java/org/elasticsearch/VersionTests.java b/server/src/test/java/org/elasticsearch/VersionTests.java
index e5149b9bce515..eb57964af4dc4 100644
--- a/server/src/test/java/org/elasticsearch/VersionTests.java
+++ b/server/src/test/java/org/elasticsearch/VersionTests.java
@@ -181,7 +181,7 @@ public void testMinCompatVersion() {
         assertThat(Version.fromString("5.3.0").minimumCompatibilityVersion(), equalTo(major5x));
 
         Version major56x = Version.fromString("5.6.0");
-        assertThat(Version.V_6_5_0.minimumCompatibilityVersion(), equalTo(major56x));
+        assertThat(Version.fromString("6.4.0").minimumCompatibilityVersion(), equalTo(major56x));
         assertThat(Version.fromString("6.3.1").minimumCompatibilityVersion(), equalTo(major56x));
 
         // from 7.0 on we are supporting the latest minor of the previous major... this might fail once we add a new version ie. 5.x is
@@ -345,10 +345,10 @@ public static void assertUnknownVersion(Version version) {
 
     public void testIsCompatible() {
         assertTrue(isCompatible(Version.CURRENT, Version.CURRENT.minimumCompatibilityVersion()));
-        assertFalse(isCompatible(Version.V_6_6_0, Version.V_7_0_0));
-        assertTrue(isCompatible(Version.V_6_8_0, Version.V_7_0_0));
+        assertFalse(isCompatible(Version.fromString("6.7.0"), Version.fromString("7.0.0")));
+        assertTrue(isCompatible(Version.fromString("6.8.0"), Version.fromString("7.0.0")));
         assertFalse(isCompatible(Version.fromId(2000099), Version.V_7_0_0));
-        assertFalse(isCompatible(Version.fromId(2000099), Version.V_6_5_0));
+        assertFalse(isCompatible(Version.fromId(2000099), Version.fromString("6.5.0")));
 
         final Version currentMajorVersion = Version.fromId(Version.CURRENT.major * 1000000 + 99);
         final Version currentOrNextMajorVersion;
diff --git a/server/src/test/java/org/elasticsearch/action/admin/cluster/state/ClusterStateRequestTests.java b/server/src/test/java/org/elasticsearch/action/admin/cluster/state/ClusterStateRequestTests.java
index f2214f4ba81fa..b219e208a6049 100644
--- a/server/src/test/java/org/elasticsearch/action/admin/cluster/state/ClusterStateRequestTests.java
+++ b/server/src/test/java/org/elasticsearch/action/admin/cluster/state/ClusterStateRequestTests.java
@@ -67,10 +67,8 @@ public void testSerialization() throws Exception {
             assertThat(deserializedCSRequest.blocks(), equalTo(clusterStateRequest.blocks()));
             assertThat(deserializedCSRequest.indices(), equalTo(clusterStateRequest.indices()));
             assertOptionsMatch(deserializedCSRequest.indicesOptions(), clusterStateRequest.indicesOptions());
-            if (testVersion.onOrAfter(Version.V_6_6_0)) {
-                assertThat(deserializedCSRequest.waitForMetaDataVersion(), equalTo(clusterStateRequest.waitForMetaDataVersion()));
-                assertThat(deserializedCSRequest.waitForTimeout(), equalTo(clusterStateRequest.waitForTimeout()));
-            }
+            assertThat(deserializedCSRequest.waitForMetaDataVersion(), equalTo(clusterStateRequest.waitForMetaDataVersion()));
+            assertThat(deserializedCSRequest.waitForTimeout(), equalTo(clusterStateRequest.waitForTimeout()));
         }
     }
 
diff --git a/server/src/test/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelperTests.java b/server/src/test/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelperTests.java
index 16740b0761ff5..2f36d315a24e9 100644
--- a/server/src/test/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelperTests.java
+++ b/server/src/test/java/org/elasticsearch/cluster/coordination/ClusterFormationFailureHelperTests.java
@@ -163,28 +163,28 @@ public void testDescriptionBeforeBootstrapping() {
             .nodes(DiscoveryNodes.builder().add(localNode).localNodeId(localNode.getId())).build();
 
         assertThat(new ClusterFormationState(Settings.EMPTY, clusterState, emptyList(), emptyList(), 1L).getDescription(),
-            is("master not discovered yet, this node has not previously joined a bootstrapped (v7+) cluster, and " +
+            is("master not discovered yet, this node has not previously joined a bootstrapped cluster, and " +
                 "[cluster.initial_master_nodes] is empty on this node: have discovered []; " +
                 "discovery will continue using [] from hosts providers and [" + localNode +
                 "] from last-known cluster state; node term 1, last-accepted version 7 in term 4"));
 
         final TransportAddress otherAddress = buildNewFakeTransportAddress();
         assertThat(new ClusterFormationState(Settings.EMPTY, clusterState, singletonList(otherAddress), emptyList(), 2L).getDescription(),
-            is("master not discovered yet, this node has not previously joined a bootstrapped (v7+) cluster, and " +
+            is("master not discovered yet, this node has not previously joined a bootstrapped cluster, and " +
                 "[cluster.initial_master_nodes] is empty on this node: have discovered []; " +
                 "discovery will continue using [" + otherAddress + "] from hosts providers and [" + localNode +
                 "] from last-known cluster state; node term 2, last-accepted version 7 in term 4"));
 
         final DiscoveryNode otherNode = new DiscoveryNode("other", buildNewFakeTransportAddress(), Version.CURRENT);
         assertThat(new ClusterFormationState(Settings.EMPTY, clusterState, emptyList(), singletonList(otherNode), 3L).getDescription(),
-            is("master not discovered yet, this node has not previously joined a bootstrapped (v7+) cluster, and " +
+            is("master not discovered yet, this node has not previously joined a bootstrapped cluster, and " +
                 "[cluster.initial_master_nodes] is empty on this node: have discovered [" + otherNode + "]; " +
                 "discovery will continue using [] from hosts providers and [" + localNode +
                 "] from last-known cluster state; node term 3, last-accepted version 7 in term 4"));
 
         assertThat(new ClusterFormationState(Settings.builder().putList(INITIAL_MASTER_NODES_SETTING.getKey(), "other").build(),
                 clusterState, emptyList(), emptyList(), 4L).getDescription(),
-            is("master not discovered yet, this node has not previously joined a bootstrapped (v7+) cluster, and " +
+            is("master not discovered yet, this node has not previously joined a bootstrapped cluster, and " +
                 "this node must discover master-eligible nodes [other] to bootstrap a cluster: have discovered []; " +
                 "discovery will continue using [] from hosts providers and [" + localNode +
                 "] from last-known cluster state; node term 4, last-accepted version 7 in term 4"));
diff --git a/server/src/test/java/org/elasticsearch/cluster/coordination/JoinTaskExecutorTests.java b/server/src/test/java/org/elasticsearch/cluster/coordination/JoinTaskExecutorTests.java
index f2bb3bd3cc03b..b8168ce3de4a7 100644
--- a/server/src/test/java/org/elasticsearch/cluster/coordination/JoinTaskExecutorTests.java
+++ b/server/src/test/java/org/elasticsearch/cluster/coordination/JoinTaskExecutorTests.java
@@ -28,7 +28,6 @@
 import org.elasticsearch.test.ESTestCase;
 import org.elasticsearch.test.VersionUtils;
 
-import static org.elasticsearch.test.VersionUtils.getPreviousVersion;
 import static org.elasticsearch.test.VersionUtils.maxCompatibleVersion;
 import static org.elasticsearch.test.VersionUtils.randomCompatibleVersion;
 import static org.elasticsearch.test.VersionUtils.randomVersionBetween;
@@ -76,7 +75,7 @@ public void testPreventJoinClusterWithUnsupportedNodeVersions() {
         final Version maxNodeVersion = nodes.getMaxNodeVersion();
         final Version minNodeVersion = nodes.getMinNodeVersion();
 
-        final Version tooLow = getPreviousVersion(maxNodeVersion.minimumCompatibilityVersion());
+        final Version tooLow = Version.fromId(maxNodeVersion.minimumCompatibilityVersion().id - 100);
         expectThrows(IllegalStateException.class, () -> {
             if (randomBoolean()) {
                 JoinTaskExecutor.ensureNodesCompatibility(tooLow, nodes);
diff --git a/server/src/test/java/org/elasticsearch/index/IndexSettingsTests.java b/server/src/test/java/org/elasticsearch/index/IndexSettingsTests.java
index b3e6557b187ae..31a92745a4245 100644
--- a/server/src/test/java/org/elasticsearch/index/IndexSettingsTests.java
+++ b/server/src/test/java/org/elasticsearch/index/IndexSettingsTests.java
@@ -564,17 +564,8 @@ public void testUpdateSoftDeletesFails() {
 
     public void testSoftDeletesDefaultSetting() {
         // enabled by default on 7.0+ or later
-        {
-            Version createdVersion = VersionUtils.randomVersionBetween(random(), Version.V_7_0_0, Version.CURRENT);
-            Settings settings = Settings.builder().put(IndexMetaData.SETTING_INDEX_VERSION_CREATED.getKey(), createdVersion).build();
-            assertTrue(IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings));
-        }
-        // disabled by default on the previous versions
-        {
-            Version prevVersion = VersionUtils.randomVersionBetween(
-                random(), Version.V_6_5_0, VersionUtils.getPreviousVersion(Version.V_7_0_0));
-            Settings settings = Settings.builder().put(IndexMetaData.SETTING_INDEX_VERSION_CREATED.getKey(), prevVersion).build();
-            assertFalse(IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings));
-        }
+        Version createdVersion = VersionUtils.randomIndexCompatibleVersion(random());
+        Settings settings = Settings.builder().put(IndexMetaData.SETTING_INDEX_VERSION_CREATED.getKey(), createdVersion).build();
+        assertTrue(IndexSettings.INDEX_SOFT_DELETES_SETTING.get(settings));
     }
 }
diff --git a/server/src/test/java/org/elasticsearch/index/query/GeoShapeQueryBuilderTests.java b/server/src/test/java/org/elasticsearch/index/query/GeoShapeQueryBuilderTests.java
index 62cc7a43cd2c2..a5311ed157c62 100644
--- a/server/src/test/java/org/elasticsearch/index/query/GeoShapeQueryBuilderTests.java
+++ b/server/src/test/java/org/elasticsearch/index/query/GeoShapeQueryBuilderTests.java
@@ -72,7 +72,7 @@ protected String fieldName() {
     @Override
     protected Settings createTestIndexSettings() {
         // force the new shape impl
-        Version version = VersionUtils.randomVersionBetween(random(), Version.V_6_6_0, Version.CURRENT);
+        Version version = VersionUtils.randomIndexCompatibleVersion(random());
         return Settings.builder()
                 .put(super.createTestIndexSettings())
                 .put(IndexMetaData.SETTING_VERSION_CREATED, version)
diff --git a/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardFollowTask.java b/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardFollowTask.java
index 5d4564a2030c1..50b32679aee0c 100644
--- a/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardFollowTask.java
+++ b/x-pack/plugin/ccr/src/main/java/org/elasticsearch/xpack/ccr/action/ShardFollowTask.java
@@ -183,6 +183,6 @@ public String toString() {
 
     @Override
     public Version getMinimalSupportedVersion() {
-        return Version.V_6_5_0;
+        return Version.CURRENT.minimumCompatibilityVersion();
     }
 }
diff --git a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/AutoFollowCoordinatorTests.java b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/AutoFollowCoordinatorTests.java
index 75e6a732c8210..7648d10aa0915 100644
--- a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/AutoFollowCoordinatorTests.java
+++ b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/AutoFollowCoordinatorTests.java
@@ -813,8 +813,7 @@ public void testAutoFollowerSoftDeletesDisabled() {
         Client client = mock(Client.class);
         when(client.getRemoteClusterClient(anyString())).thenReturn(client);
 
-        ClusterState remoteState = randomBoolean() ? createRemoteClusterState("logs-20190101", false) :
-            createRemoteClusterState("logs-20190101", null);
+        ClusterState remoteState = createRemoteClusterState("logs-20190101", false);
 
         AutoFollowPattern autoFollowPattern = new AutoFollowPattern("remote", Collections.singletonList("logs-*"),
             null, null, null, null, null, null, null, null, null, null, null);
@@ -953,13 +952,9 @@ void cleanFollowedRemoteIndices(ClusterState remoteClusterState, List<String> pa
         assertThat(entries.get(0).getValue(), nullValue());
     }
 
-    private static ClusterState createRemoteClusterState(String indexName, Boolean enableSoftDeletes) {
+    private static ClusterState createRemoteClusterState(String indexName, boolean enableSoftDeletes) {
         Settings.Builder indexSettings;
-        if (enableSoftDeletes != null) {
-            indexSettings = settings(Version.CURRENT).put(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), enableSoftDeletes);
-        } else {
-            indexSettings = settings(Version.V_6_6_0);
-        }
+        indexSettings = settings(Version.CURRENT).put(IndexSettings.INDEX_SOFT_DELETES_SETTING.getKey(), enableSoftDeletes);
 
         IndexMetaData indexMetaData = IndexMetaData.builder(indexName)
             .settings(indexSettings)
diff --git a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowActionTests.java b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowActionTests.java
index 44f8583bb9b5a..6a4e4d4b6cf0b 100644
--- a/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowActionTests.java
+++ b/x-pack/plugin/ccr/src/test/java/org/elasticsearch/xpack/ccr/action/TransportResumeFollowActionTests.java
@@ -16,7 +16,6 @@
 import org.elasticsearch.index.MapperTestUtils;
 import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.test.ESTestCase;
-import org.elasticsearch.test.VersionUtils;
 import org.elasticsearch.xpack.ccr.Ccr;
 import org.elasticsearch.xpack.ccr.CcrSettings;
 import org.elasticsearch.xpack.ccr.IndexFollowingIT;
@@ -79,16 +78,6 @@ public void testValidation() throws IOException {
             Exception e = expectThrows(IllegalArgumentException.class, () -> validate(request, leaderIMD, followIMD, UUIDs, null));
             assertThat(e.getMessage(), equalTo("leader index [index1] does not have soft deletes enabled"));
         }
-        {
-            // should fail because leader index does not have soft deletes enabled (by default).
-            Version prevVersion = VersionUtils.randomVersionBetween(
-                random(), Version.V_6_5_0, VersionUtils.getPreviousVersion(Version.V_7_0_0));
-            IndexMetaData leaderIMD = IndexMetaData.builder("index1").settings(settings(prevVersion)).numberOfShards(1)
-                .numberOfReplicas(0).setRoutingNumShards(1).putMapping("_doc", "{\"properties\": {}}").build();
-            IndexMetaData followIMD = createIMD("index2", 5, Settings.EMPTY, customMetaData);
-            Exception e = expectThrows(IllegalArgumentException.class, () -> validate(request, leaderIMD, followIMD, UUIDs, null));
-            assertThat(e.getMessage(), equalTo("leader index [index1] does not have soft deletes enabled"));
-        }
         {
             // should fail because the follower index does not have soft deletes enabled
             IndexMetaData leaderIMD = createIMD("index1", 5, Settings.EMPTY, null);
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowMetadata.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowMetadata.java
index a8758ed6c2d5a..b06ba584178c0 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowMetadata.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowMetadata.java
@@ -120,7 +120,7 @@ public String getWriteableName() {
 
     @Override
     public Version getMinimalSupportedVersion() {
-        return Version.V_6_5_0.minimumCompatibilityVersion();
+        return Version.CURRENT.minimumCompatibilityVersion();
     }
 
     @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowStats.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowStats.java
index 6c605ede85e24..879c8d79cd548 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowStats.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ccr/AutoFollowStats.java
@@ -6,7 +6,6 @@
 package org.elasticsearch.xpack.core.ccr;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -19,7 +18,6 @@
 
 import java.io.IOException;
 import java.util.AbstractMap;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.NavigableMap;
@@ -118,12 +116,8 @@ public AutoFollowStats(StreamInput in) throws IOException {
         numberOfSuccessfulFollowIndices = in.readVLong();
         // note: the casts to the following Writeable.Reader<T> instances are needed by some IDEs (e.g. Eclipse 4.8) as a compiler help
         recentAutoFollowErrors = new TreeMap<>(in.readMap((Writeable.Reader<String>) StreamInput::readString,
-                (Writeable.Reader<Tuple<Long, ElasticsearchException>>) in1 -> new Tuple<>(in1.readZLong(), in1.readException())));
-        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-            autoFollowedClusters = new TreeMap<>(in.readMap(StreamInput::readString, AutoFollowedCluster::new));
-        } else {
-            autoFollowedClusters = Collections.emptyNavigableMap();
-        }
+            (Writeable.Reader<Tuple<Long, ElasticsearchException>>) in1 -> new Tuple<>(in1.readZLong(), in1.readException())));
+        autoFollowedClusters = new TreeMap<>(in.readMap(StreamInput::readString, AutoFollowedCluster::new));
     }
 
     @Override
@@ -135,10 +129,7 @@ public void writeTo(StreamOutput out) throws IOException {
             out1.writeZLong(value.v1());
             out1.writeException(value.v2());
         });
-
-        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-            out.writeMap(autoFollowedClusters, StreamOutput::writeString, (out1, value) -> value.writeTo(out1));
-        }
+        out.writeMap(autoFollowedClusters, StreamOutput::writeString, (out1, value) -> value.writeTo(out1));
     }
 
     public long getNumberOfFailedFollowIndices() {
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexing/IndexerJobStats.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexing/IndexerJobStats.java
index 2ef9d242d9ef4..72134b0553b98 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexing/IndexerJobStats.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexing/IndexerJobStats.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.indexing;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -61,14 +60,12 @@ public IndexerJobStats(StreamInput in) throws IOException {
         this.numInputDocuments = in.readVLong();
         this.numOuputDocuments = in.readVLong();
         this.numInvocations = in.readVLong();
-        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-            this.indexTime = in.readVLong();
-            this.searchTime = in.readVLong();
-            this.indexTotal = in.readVLong();
-            this.searchTotal = in.readVLong();
-            this.indexFailures = in.readVLong();
-            this.searchFailures = in.readVLong();
-        }
+        this.indexTime = in.readVLong();
+        this.searchTime = in.readVLong();
+        this.indexTotal = in.readVLong();
+        this.searchTotal = in.readVLong();
+        this.indexFailures = in.readVLong();
+        this.searchFailures = in.readVLong();
     }
 
     public long getNumPages() {
@@ -163,14 +160,12 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeVLong(numInputDocuments);
         out.writeVLong(numOuputDocuments);
         out.writeVLong(numInvocations);
-        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-            out.writeVLong(indexTime);
-            out.writeVLong(searchTime);
-            out.writeVLong(indexTotal);
-            out.writeVLong(searchTotal);
-            out.writeVLong(indexFailures);
-            out.writeVLong(searchFailures);
-        }
+        out.writeVLong(indexTime);
+        out.writeVLong(searchTime);
+        out.writeVLong(indexTotal);
+        out.writeVLong(searchTotal);
+        out.writeVLong(indexFailures);
+        out.writeVLong(searchFailures);
     }
 
     @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/IndexLifecycleMetadata.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/IndexLifecycleMetadata.java
index c0cafa8e9079e..161033601ee3f 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/IndexLifecycleMetadata.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/indexlifecycle/IndexLifecycleMetadata.java
@@ -106,7 +106,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
 
     @Override
     public Version getMinimalSupportedVersion() {
-        return Version.V_6_6_0;
+        return Version.CURRENT.minimumCompatibilityVersion();
     }
 
     @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/OpenJobAction.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/OpenJobAction.java
index 418ae16d3e632..4468baac6e5c7 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/OpenJobAction.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/OpenJobAction.java
@@ -170,9 +170,7 @@ public JobParams(String jobId) {
         public JobParams(StreamInput in) throws IOException {
             jobId = in.readString();
             timeout = TimeValue.timeValueMillis(in.readVLong());
-            if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-                job = in.readOptionalWriteable(Job::new);
-            }
+            job = in.readOptionalWriteable(Job::new);
         }
 
         public String getJobId() {
@@ -209,9 +207,7 @@ public String getWriteableName() {
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(jobId);
             out.writeVLong(timeout.millis());
-            if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-                out.writeOptionalWriteable(job);
-            }
+            out.writeOptionalWriteable(job);
         }
 
         @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/StartDatafeedAction.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/StartDatafeedAction.java
index cdfdf06bf85ac..0ba35e6b521e2 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/StartDatafeedAction.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/action/StartDatafeedAction.java
@@ -195,10 +195,8 @@ public DatafeedParams(StreamInput in) throws IOException {
             startTime = in.readVLong();
             endTime = in.readOptionalLong();
             timeout = TimeValue.timeValueMillis(in.readVLong());
-            if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-                jobId = in.readOptionalString();
-                datafeedIndices = in.readStringList();
-            }
+            jobId = in.readOptionalString();
+            datafeedIndices = in.readStringList();
         }
 
         DatafeedParams() {
@@ -272,10 +270,8 @@ public void writeTo(StreamOutput out) throws IOException {
             out.writeVLong(startTime);
             out.writeOptionalLong(endTime);
             out.writeVLong(timeout.millis());
-            if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-                out.writeOptionalString(jobId);
-                out.writeStringCollection(datafeedIndices);
-            }
+            out.writeOptionalString(jobId);
+            out.writeStringCollection(datafeedIndices);
         }
 
         @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java
index f08c4a9d7391d..6889f5199526d 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedConfig.java
@@ -8,7 +8,6 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.Version;
 import org.elasticsearch.cluster.AbstractDiffable;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.Strings;
@@ -204,12 +203,6 @@ public DatafeedConfig(StreamInput in) throws IOException {
         } else {
             this.indices = null;
         }
-        // This consumes the list of types if there was one.
-        if (in.getVersion().before(Version.V_7_0_0)) {
-            if (in.readBoolean()) {
-                in.readStringList();
-            }
-        }
         // each of these writables are version aware
         this.queryProvider = QueryProvider.fromStream(in);
         // This reads a boolean from the stream, if true, it sends the stream to the `fromStream` method
@@ -223,11 +216,7 @@ public DatafeedConfig(StreamInput in) throws IOException {
         this.scrollSize = in.readOptionalVInt();
         this.chunkingConfig = in.readOptionalWriteable(ChunkingConfig::new);
         this.headers = Collections.unmodifiableMap(in.readMap(StreamInput::readString, StreamInput::readString));
-        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-            delayedDataCheckConfig = in.readOptionalWriteable(DelayedDataCheckConfig::new);
-        } else {
-            delayedDataCheckConfig = DelayedDataCheckConfig.defaultDelayedDataCheckConfig();
-        }
+        delayedDataCheckConfig = in.readOptionalWriteable(DelayedDataCheckConfig::new);
     }
 
     /**
@@ -408,12 +397,6 @@ public void writeTo(StreamOutput out) throws IOException {
         } else {
             out.writeBoolean(false);
         }
-        // Write the now removed types to prior versions.
-        // An empty list is expected
-        if (out.getVersion().before(Version.V_7_0_0)) {
-            out.writeBoolean(true);
-            out.writeStringCollection(Collections.emptyList());
-        }
 
         // Each of these writables are version aware
         queryProvider.writeTo(out); // never null
@@ -429,9 +412,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalVInt(scrollSize);
         out.writeOptionalWriteable(chunkingConfig);
         out.writeMap(headers, StreamOutput::writeString, StreamOutput::writeString);
-        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-            out.writeOptionalWriteable(delayedDataCheckConfig);
-        }
+        out.writeOptionalWriteable(delayedDataCheckConfig);
     }
 
     @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedUpdate.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedUpdate.java
index ccbb516197217..c1005bb971a56 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedUpdate.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/datafeed/DatafeedUpdate.java
@@ -134,11 +134,7 @@ public DatafeedUpdate(StreamInput in) throws IOException {
         }
         this.scrollSize = in.readOptionalVInt();
         this.chunkingConfig = in.readOptionalWriteable(ChunkingConfig::new);
-        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-            delayedDataCheckConfig = in.readOptionalWriteable(DelayedDataCheckConfig::new);
-        } else {
-            delayedDataCheckConfig = null;
-        }
+        delayedDataCheckConfig = in.readOptionalWriteable(DelayedDataCheckConfig::new);
     }
 
     /**
@@ -181,9 +177,7 @@ public void writeTo(StreamOutput out) throws IOException {
         }
         out.writeOptionalVInt(scrollSize);
         out.writeOptionalWriteable(chunkingConfig);
-        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-            out.writeOptionalWriteable(delayedDataCheckConfig);
-        }
+        out.writeOptionalWriteable(delayedDataCheckConfig);
     }
 
     @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/JobUpdate.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/JobUpdate.java
index b50b7d2fa5126..c1058e9c0639e 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/JobUpdate.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/config/JobUpdate.java
@@ -132,11 +132,7 @@ public JobUpdate(StreamInput in) throws IOException {
         } else {
             jobVersion = null;
         }
-        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-            clearJobFinishTime = in.readOptionalBoolean();
-        } else {
-            clearJobFinishTime = null;
-        }
+        clearJobFinishTime = in.readOptionalBoolean();
         if (in.getVersion().onOrAfter(Version.V_7_0_0) && in.readBoolean()) {
             modelSnapshotMinVersion = Version.readVersion(in);
         } else {
@@ -172,9 +168,7 @@ public void writeTo(StreamOutput out) throws IOException {
         } else {
             out.writeBoolean(false);
         }
-        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-            out.writeOptionalBoolean(clearJobFinishTime);
-        }
+        out.writeOptionalBoolean(clearJobFinishTime);
         if (out.getVersion().onOrAfter(Version.V_7_0_0)) {
             if (modelSnapshotMinVersion != null) {
                 out.writeBoolean(true);
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/AnomalyRecord.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/AnomalyRecord.java
index 3c099e309243b..5026c387e0870 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/AnomalyRecord.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/AnomalyRecord.java
@@ -18,7 +18,6 @@
 import org.elasticsearch.xpack.core.ml.job.config.Job;
 import org.elasticsearch.xpack.core.ml.utils.ExceptionsHelper;
 import org.elasticsearch.xpack.core.ml.utils.time.TimeUtils;
-import org.elasticsearch.Version;
 
 import java.io.IOException;
 import java.util.ArrayList;
@@ -160,9 +159,7 @@ public AnomalyRecord(StreamInput in) throws IOException {
         jobId = in.readString();
         detectorIndex = in.readInt();
         probability = in.readDouble();
-        if (in.getVersion().onOrAfter(Version.V_6_5_0)) {
-            multiBucketImpact = in.readOptionalDouble();
-        }
+        multiBucketImpact = in.readOptionalDouble();
         byFieldName = in.readOptionalString();
         byFieldValue = in.readOptionalString();
         correlatedByFieldValue = in.readOptionalString();
@@ -197,9 +194,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeString(jobId);
         out.writeInt(detectorIndex);
         out.writeDouble(probability);
-        if (out.getVersion().onOrAfter(Version.V_6_5_0)) {
-            out.writeOptionalDouble(multiBucketImpact);
-        }
+        out.writeOptionalDouble(multiBucketImpact);
         out.writeOptionalString(byFieldName);
         out.writeOptionalString(byFieldValue);
         out.writeOptionalString(correlatedByFieldValue);
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/Bucket.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/Bucket.java
index 8e04e001ed6cd..e34bc648cadae 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/Bucket.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/job/results/Bucket.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.ml.job.results;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -134,10 +133,6 @@ public Bucket(StreamInput in) throws IOException {
         isInterim = in.readBoolean();
         bucketInfluencers = in.readList(BucketInfluencer::new);
         processingTimeMs = in.readLong();
-        // bwc for perPartitionNormalization
-        if (in.getVersion().before(Version.V_6_5_0)) {
-            in.readList(Bucket::readOldPerPartitionNormalization);
-        }
         scheduledEvents = in.readStringList();
         if (scheduledEvents.isEmpty()) {
             scheduledEvents = Collections.emptyList();
@@ -156,10 +151,6 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeBoolean(isInterim);
         out.writeList(bucketInfluencers);
         out.writeLong(processingTimeMs);
-        // bwc for perPartitionNormalization
-        if (out.getVersion().before(Version.V_6_5_0)) {
-            out.writeList(Collections.emptyList());
-        }
         out.writeStringCollection(scheduledEvents);
     }
 
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/rollup/action/StopRollupJobAction.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/rollup/action/StopRollupJobAction.java
index 6fc079e0328c9..6b4a743ef2b3f 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/rollup/action/StopRollupJobAction.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/rollup/action/StopRollupJobAction.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.rollup.action;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.action.Action;
 import org.elasticsearch.action.ActionRequestBuilder;
 import org.elasticsearch.action.ActionRequestValidationException;
@@ -70,20 +69,16 @@ public Request() {}
         public Request(StreamInput in) throws IOException {
             super(in);
             id = in.readString();
-            if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
-                waitForCompletion = in.readBoolean();
-                timeout = in.readTimeValue();
-            }
+            waitForCompletion = in.readBoolean();
+            timeout = in.readTimeValue();
         }
 
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             super.writeTo(out);
             out.writeString(id);
-            if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
-                out.writeBoolean(waitForCompletion);
-                out.writeTimeValue(timeout);
-            }
+            out.writeBoolean(waitForCompletion);
+            out.writeTimeValue(timeout);
         }
 
         public String getId() {
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenRequest.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenRequest.java
index 3fdfaab060542..edbfce3d17aa6 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenRequest.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenRequest.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.security.action.token;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionRequest;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.common.Nullable;
@@ -186,11 +185,6 @@ public String getRefreshToken() {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        if (out.getVersion().before(Version.V_6_5_0) && GrantType.CLIENT_CREDENTIALS.getValue().equals(grantType)) {
-            throw new IllegalArgumentException("a request with the client_credentials grant_type cannot be sent to version [" +
-                out.getVersion() + "]");
-        }
-
         out.writeString(grantType);
         out.writeOptionalString(username);
         if (password == null) {
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenResponse.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenResponse.java
index 93ddc56459677..f3b094b1fd141 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenResponse.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/action/token/CreateTokenResponse.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.security.action.token;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -59,9 +58,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeString(tokenString);
         out.writeTimeValue(expiresIn);
         out.writeOptionalString(scope);
-        if (out.getVersion().onOrAfter(Version.V_6_5_0)) {
-            out.writeOptionalString(refreshToken);
-        }
+        out.writeOptionalString(refreshToken);
     }
 
     @Override
@@ -70,9 +67,7 @@ public void readFrom(StreamInput in) throws IOException {
         tokenString = in.readString();
         expiresIn = in.readTimeValue();
         scope = in.readOptionalString();
-        if (in.getVersion().onOrAfter(Version.V_6_5_0)) {
-            refreshToken = in.readOptionalString();
-        }
+        refreshToken = in.readOptionalString();
     }
 
     @Override
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/APMSystemUser.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/APMSystemUser.java
index a63c3b0dc8ca1..e4fa627fb7ab4 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/APMSystemUser.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/APMSystemUser.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.security.user;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.xpack.core.security.support.MetadataUtils;
 
 /**
@@ -15,7 +14,6 @@ public class APMSystemUser extends User {
 
     public static final String NAME = UsernamesField.APM_NAME;
     public static final String ROLE_NAME = UsernamesField.APM_ROLE;
-    public static final Version DEFINED_SINCE = Version.V_6_5_0;
 
     public APMSystemUser(boolean enabled) {
         super(NAME, new String[]{ ROLE_NAME }, null, null, MetadataUtils.DEFAULT_RESERVED_METADATA, enabled);
diff --git a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/RemoteMonitoringUser.java b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/RemoteMonitoringUser.java
index ad51c575d72d9..edfa9a8f5b8ca 100644
--- a/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/RemoteMonitoringUser.java
+++ b/x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/RemoteMonitoringUser.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.core.security.user;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.xpack.core.security.support.MetadataUtils;
 
 /**
@@ -17,8 +16,6 @@ public class RemoteMonitoringUser extends User {
     public static final String COLLECTION_ROLE_NAME = UsernamesField.REMOTE_MONITORING_COLLECTION_ROLE;
     public static final String INDEXING_ROLE_NAME = UsernamesField.REMOTE_MONITORING_INDEXING_ROLE;
 
-    public static final Version DEFINED_SINCE = Version.V_6_5_0;
-
     public RemoteMonitoringUser(boolean enabled) {
         super(NAME, new String[]{ COLLECTION_ROLE_NAME, INDEXING_ROLE_NAME }, null, null, MetadataUtils.DEFAULT_RESERVED_METADATA, enabled);
     }
diff --git a/x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/indexlifecycle/IndexLifecycleMetadataTests.java b/x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/indexlifecycle/IndexLifecycleMetadataTests.java
index 2444cbf99fd52..65f8399a6bd76 100644
--- a/x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/indexlifecycle/IndexLifecycleMetadataTests.java
+++ b/x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/indexlifecycle/IndexLifecycleMetadataTests.java
@@ -17,6 +17,7 @@
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.test.AbstractDiffableSerializationTestCase;
+import org.elasticsearch.test.VersionUtils;
 import org.elasticsearch.xpack.core.indexlifecycle.AllocateAction;
 import org.elasticsearch.xpack.core.indexlifecycle.DeleteAction;
 import org.elasticsearch.xpack.core.indexlifecycle.ForceMergeAction;
@@ -137,7 +138,8 @@ protected Reader<Diff<Custom>> diffReader() {
     }
 
     public void testMinimumSupportedVersion() {
-        assertEquals(Version.V_6_6_0, createTestInstance().getMinimalSupportedVersion());
+        Version min = createTestInstance().getMinimalSupportedVersion();
+        assertTrue(min.onOrBefore(VersionUtils.randomCompatibleVersion(random(), Version.CURRENT)));
     }
 
     public void testcontext() {
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheck.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheck.java
index daa143ec01977..1c1a28dc8943e 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheck.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheck.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.ml;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.routing.IndexRoutingTable;
 import org.elasticsearch.cluster.service.ClusterService;
@@ -23,8 +22,6 @@
  */
 public class MlConfigMigrationEligibilityCheck {
 
-    private static final Version MIN_NODE_VERSION = Version.V_6_6_0;
-
     public static final Setting<Boolean> ENABLE_CONFIG_MIGRATION = Setting.boolSetting(
         "xpack.ml.enable_config_migration", true, Setting.Property.Dynamic, Setting.Property.NodeScope);
 
@@ -43,7 +40,6 @@ private void setConfigMigrationEnabled(boolean configMigrationEnabled) {
     /**
      * Can migration start? Returns:
      *     False if config migration is disabled via the setting {@link #ENABLE_CONFIG_MIGRATION}
-     *     False if the min node version of the cluster is before {@link #MIN_NODE_VERSION}
      *     False if the .ml-config index shards are not active
      *     True otherwise
      * @param clusterState The cluster state
@@ -53,12 +49,6 @@ public boolean canStartMigration(ClusterState clusterState) {
         if (isConfigMigrationEnabled == false) {
             return false;
         }
-
-        Version minNodeVersion = clusterState.nodes().getMinNodeVersion();
-        if (minNodeVersion.before(MIN_NODE_VERSION)) {
-            return false;
-        }
-
         return mlConfigIndexIsAllocated(clusterState);
     }
 
diff --git a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/process/normalizer/NormalizerResult.java b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/process/normalizer/NormalizerResult.java
index 269792dbe7797..43f87f33ed7a4 100644
--- a/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/process/normalizer/NormalizerResult.java
+++ b/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/job/process/normalizer/NormalizerResult.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.ml.job.process.normalizer;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.common.ParseField;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -66,9 +65,7 @@ public NormalizerResult(StreamInput in) throws IOException {
         partitionFieldName = in.readOptionalString();
         partitionFieldValue = in.readOptionalString();
         personFieldName = in.readOptionalString();
-        if (in.getVersion().onOrAfter(Version.V_6_5_0)) {
-            personFieldValue = in.readOptionalString();
-        }
+        personFieldValue = in.readOptionalString();
         functionName = in.readOptionalString();
         valueFieldName = in.readOptionalString();
         probability = in.readDouble();
@@ -81,9 +78,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalString(partitionFieldName);
         out.writeOptionalString(partitionFieldValue);
         out.writeOptionalString(personFieldName);
-        if (out.getVersion().onOrAfter(Version.V_6_5_0)) {
-            out.writeOptionalString(personFieldValue);
-        }
+        out.writeOptionalString(personFieldValue);
         out.writeOptionalString(functionName);
         out.writeOptionalString(valueFieldName);
         out.writeDouble(probability);
diff --git a/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheckTests.java b/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheckTests.java
index 4d07a93e1019c..de8eb5bb2eb63 100644
--- a/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheckTests.java
+++ b/x-pack/plugin/ml/src/test/java/org/elasticsearch/xpack/ml/MlConfigMigrationEligibilityCheckTests.java
@@ -10,8 +10,6 @@
 import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.metadata.IndexMetaData;
 import org.elasticsearch.cluster.metadata.MetaData;
-import org.elasticsearch.cluster.node.DiscoveryNode;
-import org.elasticsearch.cluster.node.DiscoveryNodes;
 import org.elasticsearch.cluster.routing.IndexRoutingTable;
 import org.elasticsearch.cluster.routing.IndexShardRoutingTable;
 import org.elasticsearch.cluster.routing.RecoverySource;
@@ -21,7 +19,6 @@
 import org.elasticsearch.cluster.service.ClusterService;
 import org.elasticsearch.common.settings.ClusterSettings;
 import org.elasticsearch.common.settings.Settings;
-import org.elasticsearch.common.transport.TransportAddress;
 import org.elasticsearch.common.xcontent.NamedXContentRegistry;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.shard.ShardId;
@@ -38,7 +35,6 @@
 import org.elasticsearch.xpack.core.ml.job.persistence.AnomalyDetectorsIndex;
 import org.junit.Before;
 
-import java.net.InetAddress;
 import java.util.Collections;
 import java.util.HashSet;
 
@@ -70,50 +66,6 @@ public void testCanStartMigration_givenMigrationIsDisabled() {
         assertFalse(check.canStartMigration(clusterState));
     }
 
-    public void testCanStartMigration_givenNodesNotUpToVersion() {
-        MetaData.Builder metaData = MetaData.builder();
-        RoutingTable.Builder routingTable = RoutingTable.builder();
-        addMlConfigIndex(metaData, routingTable);
-
-        // mixed 6.5 and 6.6 nodes
-        ClusterState clusterState = ClusterState.builder(new ClusterName("_name"))
-                .nodes(DiscoveryNodes.builder()
-                        .add(new DiscoveryNode("node_id1", new TransportAddress(InetAddress.getLoopbackAddress(), 9300), Version.V_6_5_0))
-                        .add(new DiscoveryNode("node_id2", new TransportAddress(InetAddress.getLoopbackAddress(), 9301), Version.V_6_6_0)))
-                .routingTable(routingTable.build())
-                .metaData(metaData)
-                .build();
-
-        Settings settings = newSettings(true);
-        givenClusterSettings(settings);
-
-        MlConfigMigrationEligibilityCheck check = new MlConfigMigrationEligibilityCheck(settings, clusterService);
-
-        assertFalse(check.canStartMigration(clusterState));
-    }
-
-    public void testCanStartMigration_givenNodesNotUpToVersionAndMigrationIsEnabled() {
-        MetaData.Builder metaData = MetaData.builder();
-        RoutingTable.Builder routingTable = RoutingTable.builder();
-        addMlConfigIndex(metaData, routingTable);
-
-        // mixed 6.5 and 6.6 nodes
-        ClusterState clusterState = ClusterState.builder(new ClusterName("_name"))
-                .nodes(DiscoveryNodes.builder()
-                        .add(new DiscoveryNode("node_id1", new TransportAddress(InetAddress.getLoopbackAddress(), 9300), Version.V_6_6_0))
-                        .add(new DiscoveryNode("node_id2", new TransportAddress(InetAddress.getLoopbackAddress(), 9301), Version.V_6_6_0)))
-                .routingTable(routingTable.build())
-                .metaData(metaData)
-                .build();
-
-        Settings settings = newSettings(true);
-        givenClusterSettings(settings);
-
-        MlConfigMigrationEligibilityCheck check = new MlConfigMigrationEligibilityCheck(settings, clusterService);
-
-        assertTrue(check.canStartMigration(clusterState));
-    }
-
     public void testCanStartMigration_givenMissingIndex() {
         Settings settings = newSettings(true);
         givenClusterSettings(settings);
@@ -159,23 +111,6 @@ private void addMlConfigIndex(MetaData.Builder metaData, RoutingTable.Builder ro
                 .addIndexShard(new IndexShardRoutingTable.Builder(shardId).addShard(shardRouting).build()));
     }
 
-
-    public void testJobIsEligibleForMigration_givenNodesNotUpToVersion() {
-        // mixed 6.5 and 6.6 nodes
-        ClusterState clusterState = ClusterState.builder(new ClusterName("_name"))
-            .nodes(DiscoveryNodes.builder()
-                .add(new DiscoveryNode("node_id1", new TransportAddress(InetAddress.getLoopbackAddress(), 9300), Version.V_6_5_0))
-                .add(new DiscoveryNode("node_id2", new TransportAddress(InetAddress.getLoopbackAddress(), 9301), Version.V_6_6_0)))
-            .build();
-
-        Settings settings = newSettings(true);
-        givenClusterSettings(settings);
-
-        MlConfigMigrationEligibilityCheck check = new MlConfigMigrationEligibilityCheck(settings, clusterService);
-
-        assertFalse(check.jobIsEligibleForMigration("pre-min-version", clusterState));
-    }
-
     public void testJobIsEligibleForMigration_givenJobNotInClusterState() {
         ClusterState clusterState = ClusterState.builder(new ClusterName("migratortests")).build();
 
@@ -306,22 +241,6 @@ public void testJobIsEligibleForMigration_givenOpenAndUnallocatedJob() {
         assertTrue(check.jobIsEligibleForMigration(openJob.getId(), clusterState));
     }
 
-    public void testDatafeedIsEligibleForMigration_givenNodesNotUpToVersion() {
-        // mixed 6.5 and 6.6 nodes
-        ClusterState clusterState = ClusterState.builder(new ClusterName("_name"))
-            .nodes(DiscoveryNodes.builder()
-                .add(new DiscoveryNode("node_id1", new TransportAddress(InetAddress.getLoopbackAddress(), 9300), Version.V_6_5_0))
-                .add(new DiscoveryNode("node_id2", new TransportAddress(InetAddress.getLoopbackAddress(), 9301), Version.V_6_6_0)))
-            .build();
-
-        Settings settings = newSettings(true);
-        givenClusterSettings(settings);
-
-        MlConfigMigrationEligibilityCheck check = new MlConfigMigrationEligibilityCheck(settings, clusterService);
-
-        assertFalse(check.datafeedIsEligibleForMigration("pre-min-version", clusterState));
-    }
-
     public void testDatafeedIsEligibleForMigration_givenDatafeedNotInClusterState() {
         ClusterState clusterState = ClusterState.builder(new ClusterName("migratortests")).build();
         Settings settings = newSettings(true);
diff --git a/x-pack/qa/full-cluster-restart/src/test/java/org/elasticsearch/xpack/restart/MlMigrationFullClusterRestartIT.java b/x-pack/qa/full-cluster-restart/src/test/java/org/elasticsearch/xpack/restart/MlMigrationFullClusterRestartIT.java
index 3c849811f5620..14f5d66a0fff2 100644
--- a/x-pack/qa/full-cluster-restart/src/test/java/org/elasticsearch/xpack/restart/MlMigrationFullClusterRestartIT.java
+++ b/x-pack/qa/full-cluster-restart/src/test/java/org/elasticsearch/xpack/restart/MlMigrationFullClusterRestartIT.java
@@ -5,7 +5,6 @@
  */
 package org.elasticsearch.xpack.restart;
 
-import org.elasticsearch.Version;
 import org.elasticsearch.client.Request;
 import org.elasticsearch.client.Response;
 import org.elasticsearch.common.Strings;
@@ -30,12 +29,10 @@
 
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
-import java.util.Arrays;
 import java.util.Base64;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 
 import static org.hamcrest.Matchers.isEmptyOrNullString;
@@ -128,10 +125,6 @@ private void oldClusterTests() throws IOException {
     }
 
     private void upgradedClusterTests() throws Exception {
-        // wait for the closed and open jobs and datafeed to be migrated
-        waitForMigration(Arrays.asList(OLD_CLUSTER_CLOSED_JOB_ID, OLD_CLUSTER_OPEN_JOB_ID),
-                Arrays.asList(OLD_CLUSTER_STOPPED_DATAFEED_ID, OLD_CLUSTER_STARTED_DATAFEED_ID));
-
         waitForJobToBeAssigned(OLD_CLUSTER_OPEN_JOB_ID);
         waitForDatafeedToBeAssigned(OLD_CLUSTER_STARTED_DATAFEED_ID);
         // The persistent task params for the job & datafeed left open
@@ -181,40 +174,6 @@ private void waitForDatafeedToBeAssigned(String datafeedId) throws Exception {
         }, 30, TimeUnit.SECONDS);
     }
 
-    @SuppressWarnings("unchecked")
-    private void waitForMigration(List<String> expectedMigratedJobs, List<String> expectedMigratedDatafeeds) throws Exception {
-
-        // After v6.6.0 jobs are created in the index so no migration will take place
-        if (getOldClusterVersion().onOrAfter(Version.V_6_6_0)) {
-            return;
-        }
-
-        assertBusy(() -> {
-            // wait for the eligible configs to be moved from the clusterstate
-            Request getClusterState = new Request("GET", "/_cluster/state/metadata");
-            Response response = client().performRequest(getClusterState);
-            Map<String, Object> responseMap = entityAsMap(response);
-
-            List<Map<String, Object>> jobs =
-                    (List<Map<String, Object>>) XContentMapValues.extractValue("metadata.ml.jobs", responseMap);
-
-            if (jobs != null) {
-                for (String jobId : expectedMigratedJobs) {
-                    assertJobNotPresent(jobId, jobs);
-                }
-            }
-
-            List<Map<String, Object>> datafeeds =
-                    (List<Map<String, Object>>) XContentMapValues.extractValue("metadata.ml.datafeeds", responseMap);
-
-            if (datafeeds != null) {
-                for (String datafeedId : expectedMigratedDatafeeds) {
-                    assertDatafeedNotPresent(datafeedId, datafeeds);
-                }
-            }
-        }, 30, TimeUnit.SECONDS);
-    }
-
     @SuppressWarnings("unchecked")
     private void checkTaskParamsAreUpdated(String jobId, String datafeedId) throws Exception {
         Request getClusterState = new Request("GET", "/_cluster/state/metadata");
@@ -240,18 +199,6 @@ else if (id.equals(MlTasks.datafeedTaskId(datafeedId))) {
         }
     }
 
-    private void assertDatafeedNotPresent(String datafeedId, List<Map<String, Object>> datafeeds) {
-        Optional<Object> config = datafeeds.stream().map(map -> map.get("datafeed_id"))
-                .filter(id -> id.equals(datafeedId)).findFirst();
-        assertFalse(config.isPresent());
-    }
-
-    private void assertJobNotPresent(String jobId, List<Map<String, Object>> jobs) {
-        Optional<Object> config = jobs.stream().map(map -> map.get("job_id"))
-                .filter(id -> id.equals(jobId)).findFirst();
-        assertFalse(config.isPresent());
-    }
-
     private void addAggregations(DatafeedConfig.Builder dfBuilder) {
         TermsAggregationBuilder airline = AggregationBuilders.terms("airline");
         MaxAggregationBuilder maxTime = AggregationBuilders.max("time").field("time").subAggregation(airline);