diff --git a/server/src/main/java/org/elasticsearch/action/RoutingMissingException.java b/server/src/main/java/org/elasticsearch/action/RoutingMissingException.java
index 5804598febd10..cb22248daa62e 100644
--- a/server/src/main/java/org/elasticsearch/action/RoutingMissingException.java
+++ b/server/src/main/java/org/elasticsearch/action/RoutingMissingException.java
@@ -10,10 +10,8 @@
 package org.elasticsearch.action;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.rest.RestStatus;
 
 import java.io.IOException;
@@ -42,18 +40,12 @@ public RestStatus status() {
 
     public RoutingMissingException(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readString();
-        }
         id = in.readString();
     }
 
     @Override
     protected void writeTo(StreamOutput out, Writer<Throwable> nestedExceptionsWriter) throws IOException {
         super.writeTo(out, nestedExceptionsWriter);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
     }
 }
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexRequest.java
index 84c040df758d3..fe2cdd482ae3d 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexRequest.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.get;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.support.IndicesOptions;
@@ -113,9 +112,6 @@ public GetIndexRequest(TimeValue masterTimeout) {
     public GetIndexRequest(StreamInput in) throws IOException {
         super(in);
         indices = in.readStringArray();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readStringArray();
-        }
         indicesOptions = IndicesOptions.readIndicesOptions(in);
         features = in.readArray(i -> Feature.fromId(i.readByte()), Feature[]::new);
         humanReadable = in.readBoolean();
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexResponse.java b/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexResponse.java
index 91f7dfd8a98f5..4a50f3b20a6c9 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/get/GetIndexResponse.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.get;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.cluster.metadata.AliasMetadata;
 import org.elasticsearch.cluster.metadata.MappingMetadata;
@@ -20,7 +19,6 @@
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.xcontent.ChunkedToXContentObject;
 import org.elasticsearch.core.UpdateForV10;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.ToXContent;
 
 import java.io.IOException;
@@ -77,18 +75,10 @@ public GetIndexResponse(
     @UpdateForV10(owner = UpdateForV10.Owner.DATA_MANAGEMENT)
     GetIndexResponse(StreamInput in) throws IOException {
         this.indices = in.readStringArray();
-        mappings = in.readImmutableOpenMap(StreamInput::readString, in.getTransportVersion().before(TransportVersions.V_8_0_0) ? i -> {
-            int numMappings = i.readVInt();
-            assert numMappings == 0 || numMappings == 1 : "Expected 0 or 1 mappings but got " + numMappings;
-            if (numMappings == 1) {
-                String type = i.readString();
-                assert MapperService.SINGLE_MAPPING_NAME.equals(type) : "Expected [_doc] but got [" + type + "]";
-                return new MappingMetadata(i);
-            } else {
-                return MappingMetadata.EMPTY_MAPPINGS;
-            }
-        } : i -> i.readBoolean() ? new MappingMetadata(i) : MappingMetadata.EMPTY_MAPPINGS);
-
+        mappings = in.readImmutableOpenMap(
+            StreamInput::readString,
+            i -> i.readBoolean() ? new MappingMetadata(i) : MappingMetadata.EMPTY_MAPPINGS
+        );
         aliases = in.readImmutableOpenMap(StreamInput::readString, i -> i.readCollectionAsList(AliasMetadata::new));
         settings = in.readImmutableOpenMap(StreamInput::readString, Settings::readSettingsFromStream);
         defaultSettings = in.readImmutableOpenMap(StreamInput::readString, Settings::readSettingsFromStream);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsIndexRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsIndexRequest.java
index 6ac78e7c27aed..829b9b8bde0b3 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsIndexRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsIndexRequest.java
@@ -9,12 +9,10 @@
 
 package org.elasticsearch.action.admin.indices.mapping.get;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.OriginalIndices;
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.action.support.single.shard.SingleShardRequest;
-import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 
@@ -29,14 +27,8 @@ public class GetFieldMappingsIndexRequest extends SingleShardRequest<GetFieldMap
 
     GetFieldMappingsIndexRequest(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readStringArray();   // former types array
-        }
         fields = in.readStringArray();
         includeDefaults = in.readBoolean();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readBoolean();       // former probablySingleField boolean
-        }
         originalIndices = OriginalIndices.readOriginalIndices(in);
     }
 
@@ -74,14 +66,8 @@ public IndicesOptions indicesOptions() {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeStringArray(Strings.EMPTY_ARRAY);
-        }
         out.writeStringArray(fields);
         out.writeBoolean(includeDefaults);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeBoolean(false);
-        }
         OriginalIndices.writeOriginalIndices(originalIndices, out);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsRequest.java
index 1bab7267b108e..423aa6e73bb31 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsRequest.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.mapping.get;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.LegacyActionRequest;
@@ -19,7 +18,6 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 
 import java.io.IOException;
-import java.util.Arrays;
 
 /**
  * Request the mappings of specific fields
@@ -42,18 +40,7 @@ public GetFieldMappingsRequest() {}
     public GetFieldMappingsRequest(StreamInput in) throws IOException {
         super(in);
         indices = in.readStringArray();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            String[] types = in.readStringArray();
-            if (types != Strings.EMPTY_ARRAY) {
-                throw new IllegalArgumentException("Expected empty type array but received [" + Arrays.toString(types) + "]");
-            }
-
-        }
         indicesOptions = IndicesOptions.readIndicesOptions(in);
-        // Consume the deprecated local parameter
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readBoolean();
-        }
         fields = in.readStringArray();
         includeDefaults = in.readBoolean();
     }
@@ -117,13 +104,7 @@ public ActionRequestValidationException validate() {
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeStringArray(indices);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeStringArray(Strings.EMPTY_ARRAY);
-        }
         indicesOptions.writeIndicesOptions(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeBoolean(true);
-        }
         out.writeStringArray(fields);
         out.writeBoolean(includeDefaults);
     }
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
index 9c0fe03e95748..78b29c87e9d89 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetFieldMappingsResponse.java
@@ -9,14 +9,12 @@
 
 package org.elasticsearch.action.admin.indices.mapping.get;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.index.mapper.Mapper;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.ToXContentFragment;
 import org.elasticsearch.xcontent.ToXContentObject;
@@ -25,7 +23,6 @@
 
 import java.io.IOException;
 import java.io.InputStream;
-import java.util.Collections;
 import java.util.Map;
 import java.util.Objects;
 
@@ -46,17 +43,9 @@ public class GetFieldMappingsResponse extends ActionResponse implements ToXConte
     }
 
     GetFieldMappingsResponse(StreamInput in) throws IOException {
-        mappings = in.readImmutableMap(mapIn -> {
-            if (mapIn.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                int typesSize = mapIn.readVInt();
-                assert typesSize == 1 || typesSize == 0 : "Expected 0 or 1 types but got " + typesSize;
-                if (typesSize == 0) {
-                    return Collections.emptyMap();
-                }
-                mapIn.readString(); // type
-            }
-            return mapIn.readImmutableMap(inpt -> new FieldMappingMetadata(inpt.readString(), inpt.readBytesReference()));
-        });
+        mappings = in.readImmutableMap(
+            mapIn -> mapIn.readImmutableMap(inpt -> new FieldMappingMetadata(inpt.readString(), inpt.readBytesReference()))
+        );
     }
 
     /** returns the retrieved field mapping. The return map keys are index, field (as specified in the request). */
@@ -134,10 +123,6 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeMap(mappings, (outpt, map) -> {
-            if (outpt.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                outpt.writeVInt(1);
-                outpt.writeString(MapperService.SINGLE_MAPPING_NAME);
-            }
             outpt.writeMap(map, (o, v) -> {
                 o.writeString(v.fullName());
                 o.writeBytesReference(v.source);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetMappingsRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetMappingsRequest.java
index ca4314b4b9922..e661c53c805a1 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetMappingsRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/get/GetMappingsRequest.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.mapping.get;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.support.IndicesOptions;
@@ -43,9 +42,6 @@ public GetMappingsRequest(TimeValue masterTimeout) {
     public GetMappingsRequest(StreamInput in) throws IOException {
         super(in);
         indices = in.readStringArray();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readStringArray();
-        }
         indicesOptions = IndicesOptions.readIndicesOptions(in);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java
index 05cc0d2cf05d8..72b2d951bc03e 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/mapping/put/PutMappingRequest.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.action.admin.indices.mapping.put;
 
 import org.elasticsearch.ElasticsearchGenerationException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.support.IndicesOptions;
@@ -24,7 +23,6 @@
 import org.elasticsearch.common.util.CollectionUtils;
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.index.Index;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xcontent.XContentFactory;
 import org.elasticsearch.xcontent.XContentType;
@@ -97,12 +95,6 @@ public PutMappingRequest(StreamInput in) throws IOException {
         super(in);
         indices = in.readStringArray();
         indicesOptions = IndicesOptions.readIndicesOptions(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            String type = in.readOptionalString();
-            if (MapperService.SINGLE_MAPPING_NAME.equals(type) == false) {
-                throw new IllegalArgumentException("Expected type [_doc] but received [" + type + "]");
-            }
-        }
         source = in.readString();
         concreteIndex = in.readOptionalWriteable(Index::new);
         origin = in.readOptionalString();
@@ -330,9 +322,6 @@ public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeStringArrayNullable(indices);
         indicesOptions.writeIndicesOptions(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(source);
         out.writeOptionalWriteable(concreteIndex);
         out.writeOptionalString(origin);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/segments/IndicesSegmentsRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/segments/IndicesSegmentsRequest.java
index bdacfb0ab642d..de9692cdaaded 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/segments/IndicesSegmentsRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/segments/IndicesSegmentsRequest.java
@@ -31,9 +31,6 @@ public IndicesSegmentsRequest() {
 
     public IndicesSegmentsRequest(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readBoolean();   // old 'verbose' option, since removed
-        }
         if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_15_0)) {
             this.includeVectorFormatsInfo = in.readBoolean();
         }
@@ -56,9 +53,6 @@ public boolean isIncludeVectorFormatsInfo() {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeBoolean(false);
-        }
         if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_15_0)) {
             out.writeBoolean(includeVectorFormatsInfo);
         }
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequest.java
index 0f11cb45e08d5..81b44b6720567 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/template/put/PutIndexTemplateRequest.java
@@ -10,7 +10,6 @@
 
 import org.elasticsearch.ElasticsearchGenerationException;
 import org.elasticsearch.ElasticsearchParseException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.admin.indices.alias.Alias;
@@ -77,15 +76,7 @@ public PutIndexTemplateRequest(StreamInput in) throws IOException {
         order = in.readInt();
         create = in.readBoolean();
         settings = readSettingsFromStream(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            int size = in.readVInt();
-            for (int i = 0; i < size; i++) {
-                in.readString();    // type - cannot assert on _doc because 7x allows arbitrary type names
-                this.mappings = in.readString();
-            }
-        } else {
-            this.mappings = in.readOptionalString();
-        }
+        mappings = in.readOptionalString();
         int aliasesSize = in.readVInt();
         for (int i = 0; i < aliasesSize; i++) {
             aliases.add(new Alias(in));
@@ -450,15 +441,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeInt(order);
         out.writeBoolean(create);
         settings.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeVInt(mappings == null ? 0 : 1);
-            if (mappings != null) {
-                out.writeString(MapperService.SINGLE_MAPPING_NAME);
-                out.writeString(mappings);
-            }
-        } else {
-            out.writeOptionalString(mappings);
-        }
+        out.writeOptionalString(mappings);
         out.writeCollection(aliases);
         out.writeOptionalVInt(version);
     }
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ShardValidateQueryRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ShardValidateQueryRequest.java
index f41cb6fbc0306..0687b0fcbbed0 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ShardValidateQueryRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ShardValidateQueryRequest.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.validate.query;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.support.broadcast.BroadcastShardRequest;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -34,14 +33,6 @@ public class ShardValidateQueryRequest extends BroadcastShardRequest {
     public ShardValidateQueryRequest(StreamInput in) throws IOException {
         super(in);
         query = in.readNamedWriteable(QueryBuilder.class);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            int typesSize = in.readVInt();
-            if (typesSize > 0) {
-                for (int i = 0; i < typesSize; i++) {
-                    in.readString();
-                }
-            }
-        }
         filteringAliases = AliasFilter.readFrom(in);
         explain = in.readBoolean();
         rewrite = in.readBoolean();
@@ -81,9 +72,6 @@ public long nowInMillis() {
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeNamedWriteable(query);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeVInt(0);   // no types to filter
-        }
         filteringAliases.writeTo(out);
         out.writeBoolean(explain);
         out.writeBoolean(rewrite);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ValidateQueryRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ValidateQueryRequest.java
index f30206c1d238a..1117b1997b739 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ValidateQueryRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/validate/query/ValidateQueryRequest.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.validate.query;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.ValidateActions;
 import org.elasticsearch.action.support.IndicesOptions;
@@ -49,14 +48,6 @@ public ValidateQueryRequest() {
     public ValidateQueryRequest(StreamInput in) throws IOException {
         super(in);
         query = in.readNamedWriteable(QueryBuilder.class);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            int typesSize = in.readVInt();
-            if (typesSize > 0) {
-                for (int i = 0; i < typesSize; i++) {
-                    in.readString();
-                }
-            }
-        }
         explain = in.readBoolean();
         rewrite = in.readBoolean();
         allShards = in.readBoolean();
@@ -138,9 +129,6 @@ public boolean allShards() {
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
         out.writeNamedWriteable(query);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeVInt(0);   // no types to filter
-        }
         out.writeBoolean(explain);
         out.writeBoolean(rewrite);
         out.writeBoolean(allShards);
diff --git a/server/src/main/java/org/elasticsearch/action/fieldcaps/IndexFieldCapabilities.java b/server/src/main/java/org/elasticsearch/action/fieldcaps/IndexFieldCapabilities.java
index 349ae476dd724..7b19c1928d535 100644
--- a/server/src/main/java/org/elasticsearch/action/fieldcaps/IndexFieldCapabilities.java
+++ b/server/src/main/java/org/elasticsearch/action/fieldcaps/IndexFieldCapabilities.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.fieldcaps;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -47,15 +46,8 @@ public static IndexFieldCapabilities readFrom(StreamInput in) throws IOException
         boolean isMetadatafield = in.readBoolean();
         boolean isSearchable = in.readBoolean();
         boolean isAggregatable = in.readBoolean();
-        boolean isDimension;
-        TimeSeriesParams.MetricType metricType;
-        if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            isDimension = in.readBoolean();
-            metricType = in.readOptionalEnum(TimeSeriesParams.MetricType.class);
-        } else {
-            isDimension = false;
-            metricType = null;
-        }
+        boolean isDimension = in.readBoolean();
+        TimeSeriesParams.MetricType metricType = in.readOptionalEnum(TimeSeriesParams.MetricType.class);
         return new IndexFieldCapabilities(
             name,
             type,
@@ -75,10 +67,8 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeBoolean(isMetadatafield);
         out.writeBoolean(isSearchable);
         out.writeBoolean(isAggregatable);
-        if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            out.writeBoolean(isDimension);
-            out.writeOptionalEnum(metricType);
-        }
+        out.writeBoolean(isDimension);
+        out.writeOptionalEnum(metricType);
         out.writeMap(meta, StreamOutput::writeString);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/action/get/GetRequest.java b/server/src/main/java/org/elasticsearch/action/get/GetRequest.java
index 9ff4e662270f9..5e87e3f561109 100644
--- a/server/src/main/java/org/elasticsearch/action/get/GetRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/get/GetRequest.java
@@ -19,7 +19,6 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.lucene.uid.Versions;
 import org.elasticsearch.index.VersionType;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.SourceLoader;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
 
@@ -67,9 +66,6 @@ public GetRequest() {}
 
     public GetRequest(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readString();
-        }
         id = in.readString();
         routing = in.readOptionalString();
         preference = in.readOptionalString();
@@ -90,9 +86,6 @@ public GetRequest(StreamInput in) throws IOException {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeOptionalString(routing);
         out.writeOptionalString(preference);
diff --git a/server/src/main/java/org/elasticsearch/action/get/MultiGetRequest.java b/server/src/main/java/org/elasticsearch/action/get/MultiGetRequest.java
index b73aaffbbf012..460475b6597dd 100644
--- a/server/src/main/java/org/elasticsearch/action/get/MultiGetRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/get/MultiGetRequest.java
@@ -26,7 +26,6 @@
 import org.elasticsearch.common.lucene.uid.Versions;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.index.VersionType;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.SourceLoader;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
 import org.elasticsearch.xcontent.ParseField;
@@ -82,9 +81,6 @@ public Item() {
 
         public Item(StreamInput in) throws IOException {
             index = in.readString();
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                in.readOptionalString();
-            }
             id = in.readString();
             routing = in.readOptionalString();
             storedFields = in.readOptionalStringArray();
@@ -176,9 +172,6 @@ public Item fetchSourceContext(FetchSourceContext fetchSourceContext) {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(index);
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-            }
             out.writeString(id);
             out.writeOptionalString(routing);
             out.writeOptionalStringArray(storedFields);
diff --git a/server/src/main/java/org/elasticsearch/action/get/MultiGetResponse.java b/server/src/main/java/org/elasticsearch/action/get/MultiGetResponse.java
index 08db6dee8e543..967762f9b2055 100644
--- a/server/src/main/java/org/elasticsearch/action/get/MultiGetResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/get/MultiGetResponse.java
@@ -10,13 +10,11 @@
 package org.elasticsearch.action.get;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.ToXContentObject;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -47,9 +45,6 @@ public Failure(String index, String id, Exception exception) {
 
         Failure(StreamInput in) throws IOException {
             index = in.readString();
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                in.readOptionalString();
-            }
             id = in.readString();
             exception = in.readException();
         }
@@ -78,9 +73,6 @@ public String getMessage() {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(index);
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-            }
             out.writeString(id);
             out.writeException(exception);
         }
diff --git a/server/src/main/java/org/elasticsearch/action/index/IndexRequest.java b/server/src/main/java/org/elasticsearch/action/index/IndexRequest.java
index 28f774b01b132..c6892eeb40411 100644
--- a/server/src/main/java/org/elasticsearch/action/index/IndexRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/index/IndexRequest.java
@@ -37,7 +37,6 @@
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.index.VersionType;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.ingest.IngestService;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -160,10 +159,6 @@ public IndexRequest(StreamInput in) throws IOException {
 
     public IndexRequest(@Nullable ShardId shardId, StreamInput in) throws IOException {
         super(shardId, in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            String type = in.readOptionalString();
-            assert MapperService.SINGLE_MAPPING_NAME.equals(type) : "Expected [_doc] but received [" + type + "]";
-        }
         id = in.readOptionalString();
         routing = in.readOptionalString();
         boolean beforeSourceContext = in.getTransportVersion().supports(INDEX_SOURCE) == false;
@@ -762,9 +757,6 @@ public void writeThin(StreamOutput out) throws IOException {
     }
 
     private void writeBody(StreamOutput out) throws IOException {
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeOptionalString(id);
         out.writeOptionalString(routing);
         if (out.getTransportVersion().supports(INDEX_SOURCE)) {
diff --git a/server/src/main/java/org/elasticsearch/action/search/SearchRequest.java b/server/src/main/java/org/elasticsearch/action/search/SearchRequest.java
index d9cfabcd45b97..981ee5c6bc161 100644
--- a/server/src/main/java/org/elasticsearch/action/search/SearchRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/search/SearchRequest.java
@@ -239,15 +239,6 @@ public SearchRequest(StreamInput in) throws IOException {
         preference = in.readOptionalString();
         scrollKeepAlive = in.readOptionalTimeValue();
         source = in.readOptionalWriteable(SearchSourceBuilder::new);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types no longer relevant so ignore
-            String[] types = in.readStringArray();
-            if (types.length > 0) {
-                throw new IllegalStateException(
-                    "types are no longer supported in search requests but found [" + Arrays.toString(types) + "]"
-                );
-            }
-        }
         indicesOptions = IndicesOptions.readIndicesOptions(in);
         requestCache = in.readOptionalBoolean();
         batchedReduceSize = in.readVInt();
@@ -291,10 +282,6 @@ public void writeTo(StreamOutput out, boolean skipIndices) throws IOException {
         out.writeOptionalString(preference);
         out.writeOptionalTimeValue(scrollKeepAlive);
         out.writeOptionalWriteable(source);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types not supported so send an empty array to previous versions
-            out.writeStringArray(Strings.EMPTY_ARRAY);
-        }
         indicesOptions.writeIndicesOptions(out);
         out.writeOptionalBoolean(requestCache);
         out.writeVInt(batchedReduceSize);
diff --git a/server/src/main/java/org/elasticsearch/action/termvectors/MultiTermVectorsResponse.java b/server/src/main/java/org/elasticsearch/action/termvectors/MultiTermVectorsResponse.java
index 42196fac28528..23996ec4976e6 100644
--- a/server/src/main/java/org/elasticsearch/action/termvectors/MultiTermVectorsResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/termvectors/MultiTermVectorsResponse.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.action.termvectors;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.collect.Iterators;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -40,13 +39,6 @@ public Failure(String index, String id, Exception cause) {
 
         public Failure(StreamInput in) throws IOException {
             index = in.readString();
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                // types no longer relevant so ignore
-                String type = in.readOptionalString();
-                if (type != null) {
-                    throw new IllegalStateException("types are no longer supported but found [" + type + "]");
-                }
-            }
             id = in.readString();
             cause = in.readException();
         }
@@ -75,10 +67,6 @@ public Exception getCause() {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(index);
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                // types not supported so send an empty array to previous versions
-                out.writeOptionalString(null);
-            }
             out.writeString(id);
             out.writeException(cause);
         }
diff --git a/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsRequest.java b/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsRequest.java
index 7a7b2afab75d1..0e410969cc639 100644
--- a/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsRequest.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.action.termvectors;
 
 import org.elasticsearch.ElasticsearchParseException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.RealtimeRequest;
 import org.elasticsearch.action.ValidateActions;
@@ -125,10 +124,6 @@ public TermVectorsRequest() {}
 
     TermVectorsRequest(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types no longer relevant so ignore
-            in.readString();
-        }
         id = in.readString();
 
         if (in.readBoolean()) {
@@ -474,10 +469,6 @@ public ActionRequestValidationException validate() {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         super.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types not supported so send an empty array to previous versions
-            out.writeString("_doc");
-        }
         out.writeString(id);
 
         out.writeBoolean(doc != null);
diff --git a/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsResponse.java b/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsResponse.java
index 4c4aa7de46f6b..1e5e0397ff957 100644
--- a/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/termvectors/TermVectorsResponse.java
@@ -17,7 +17,6 @@
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.CharsRefBuilder;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.action.termvectors.TermVectorsRequest.Flag;
 import org.elasticsearch.common.bytes.BytesArray;
@@ -26,7 +25,6 @@
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.core.TimeValue;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.ToXContentObject;
 import org.elasticsearch.xcontent.XContentBuilder;
 
@@ -87,10 +85,6 @@ public TermVectorsResponse(String index, String id) {
 
     TermVectorsResponse(StreamInput in) throws IOException {
         index = in.readString();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types no longer relevant so ignore
-            in.readString();
-        }
         id = in.readString();
         docVersion = in.readVLong();
         exists = in.readBoolean();
@@ -105,10 +99,6 @@ public TermVectorsResponse(String index, String id) {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(index);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types not supported so send an empty array to previous versions
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeVLong(docVersion);
         final boolean docExists = isExists();
diff --git a/server/src/main/java/org/elasticsearch/action/update/UpdateRequest.java b/server/src/main/java/org/elasticsearch/action/update/UpdateRequest.java
index 657ad029626af..079b6611119b2 100644
--- a/server/src/main/java/org/elasticsearch/action/update/UpdateRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/update/UpdateRequest.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.action.update;
 
 import org.apache.lucene.util.RamUsageEstimator;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.DocWriteRequest;
 import org.elasticsearch.action.index.IndexRequest;
@@ -28,7 +27,6 @@
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.index.VersionType;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.script.Script;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
@@ -135,10 +133,6 @@ public UpdateRequest(StreamInput in) throws IOException {
     public UpdateRequest(@Nullable ShardId shardId, StreamInput in) throws IOException {
         super(shardId, in);
         waitForActiveShards = ActiveShardCount.readFrom(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            String type = in.readString();
-            assert MapperService.SINGLE_MAPPING_NAME.equals(type) : "Expected [_doc] but received [" + type + "]";
-        }
         id = in.readString();
         routing = in.readOptionalString();
         if (in.readBoolean()) {
@@ -707,9 +701,6 @@ public void writeThin(StreamOutput out) throws IOException {
 
     private void doWrite(StreamOutput out, boolean thin) throws IOException {
         waitForActiveShards.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeOptionalString(routing);
 
diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/MappingMetadata.java b/server/src/main/java/org/elasticsearch/cluster/metadata/MappingMetadata.java
index ee4869508eaf2..1b3dbcc9a50e9 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/MappingMetadata.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/MappingMetadata.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.cluster.metadata;
 
 import org.elasticsearch.ElasticsearchParseException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.cluster.Diff;
 import org.elasticsearch.cluster.SimpleDiffable;
 import org.elasticsearch.common.compress.CompressedXContent;
@@ -76,13 +75,7 @@ public MappingMetadata(String type, Map<String, Object> mapping) {
     }
 
     public static void writeMappingMetadata(StreamOutput out, Map<String, MappingMetadata> mappings) throws IOException {
-        out.writeMap(mappings, out.getTransportVersion().before(TransportVersions.V_8_0_0) ? (o, v) -> {
-            o.writeVInt(v == EMPTY_MAPPINGS ? 0 : 1);
-            if (v != EMPTY_MAPPINGS) {
-                o.writeString(MapperService.SINGLE_MAPPING_NAME);
-                v.writeTo(o);
-            }
-        } : (o, v) -> {
+        out.writeMap(mappings, (o, v) -> {
             o.writeBoolean(v != EMPTY_MAPPINGS);
             if (v != EMPTY_MAPPINGS) {
                 v.writeTo(o);
diff --git a/server/src/main/java/org/elasticsearch/common/xcontent/XContentHelper.java b/server/src/main/java/org/elasticsearch/common/xcontent/XContentHelper.java
index f62fa6abff3a7..0215fb1e97686 100644
--- a/server/src/main/java/org/elasticsearch/common/xcontent/XContentHelper.java
+++ b/server/src/main/java/org/elasticsearch/common/xcontent/XContentHelper.java
@@ -11,7 +11,6 @@
 
 import org.elasticsearch.ElasticsearchGenerationException;
 import org.elasticsearch.ElasticsearchParseException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
@@ -744,12 +743,7 @@ public static BytesReference childBytes(XContentParser parser) throws IOExceptio
      * @param xContentType an instance to serialize
      */
     public static void writeTo(StreamOutput out, XContentType xContentType) throws IOException {
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // when sending an enumeration to <v8 node it does not have new VND_ XContentType instances
-            out.writeVInt(xContentType.canonical().ordinal());
-        } else {
-            out.writeVInt(xContentType.ordinal());
-        }
+        out.writeVInt(xContentType.ordinal());
     }
 
     /**
diff --git a/server/src/main/java/org/elasticsearch/gateway/LocalAllocateDangledIndices.java b/server/src/main/java/org/elasticsearch/gateway/LocalAllocateDangledIndices.java
index 0727ad1bade7f..d0c8425a0b128 100644
--- a/server/src/main/java/org/elasticsearch/gateway/LocalAllocateDangledIndices.java
+++ b/server/src/main/java/org/elasticsearch/gateway/LocalAllocateDangledIndices.java
@@ -11,7 +11,6 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.ActionListenerResponseHandler;
 import org.elasticsearch.action.support.ChannelActionListener;
@@ -277,19 +276,11 @@ public void writeTo(StreamOutput out) throws IOException {
 
     public static class AllocateDangledResponse extends TransportResponse {
 
-        private AllocateDangledResponse(StreamInput in) throws IOException {
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                in.readBoolean();
-            }
-        }
+        private AllocateDangledResponse(StreamInput in) throws IOException {}
 
         private AllocateDangledResponse() {}
 
         @Override
-        public void writeTo(StreamOutput out) throws IOException {
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                out.writeBoolean(true);
-            }
-        }
+        public void writeTo(StreamOutput out) throws IOException {}
     }
 }
diff --git a/server/src/main/java/org/elasticsearch/index/engine/Segment.java b/server/src/main/java/org/elasticsearch/index/engine/Segment.java
index 8afb7033f87d8..11f8cfec74e35 100644
--- a/server/src/main/java/org/elasticsearch/index/engine/Segment.java
+++ b/server/src/main/java/org/elasticsearch/index/engine/Segment.java
@@ -53,9 +53,6 @@ public Segment(StreamInput in) throws IOException {
         version = Lucene.parseVersionLenient(in.readOptionalString(), null);
         compound = in.readOptionalBoolean();
         mergeId = in.readOptionalString();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readLong(); // memoryInBytes
-        }
         if (in.readBoolean()) {
             readRamTree(in);
         }
@@ -160,10 +157,6 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalString(version.toString());
         out.writeOptionalBoolean(compound);
         out.writeOptionalString(mergeId);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeLong(0); // memoryInBytes
-        }
-
         out.writeBoolean(false);
         writeSegmentSort(out, segmentSort);
         boolean hasAttributes = attributes != null;
diff --git a/server/src/main/java/org/elasticsearch/index/engine/SegmentsStats.java b/server/src/main/java/org/elasticsearch/index/engine/SegmentsStats.java
index d54f21193afe6..dda5d5116fb60 100644
--- a/server/src/main/java/org/elasticsearch/index/engine/SegmentsStats.java
+++ b/server/src/main/java/org/elasticsearch/index/engine/SegmentsStats.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.index.engine;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -40,15 +39,6 @@ public SegmentsStats() {
 
     public SegmentsStats(StreamInput in) throws IOException {
         count = in.readVLong();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readLong(); // memoryInBytes
-            in.readLong(); // termsMemoryInBytes
-            in.readLong(); // storedFieldsMemoryInBytes
-            in.readLong(); // termVectorsMemoryInBytes
-            in.readLong(); // normsMemoryInBytes
-            in.readLong(); // pointsMemoryInBytes
-            in.readLong(); // docValuesMemoryInBytes
-        }
         indexWriterMemoryInBytes = in.readLong();
         versionMapMemoryInBytes = in.readLong();
         bitsetMemoryInBytes = in.readLong();
@@ -221,15 +211,6 @@ static final class Fields {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeVLong(count);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeLong(0L); // memoryInBytes
-            out.writeLong(0L); // termsMemoryInBytes
-            out.writeLong(0L); // storedFieldsMemoryInBytes
-            out.writeLong(0L); // termVectorsMemoryInBytes
-            out.writeLong(0L); // normsMemoryInBytes
-            out.writeLong(0L); // pointsMemoryInBytes
-            out.writeLong(0L); // docValuesMemoryInBytes
-        }
         out.writeLong(indexWriterMemoryInBytes);
         out.writeLong(versionMapMemoryInBytes);
         out.writeLong(bitsetMemoryInBytes);
diff --git a/server/src/main/java/org/elasticsearch/index/get/GetResult.java b/server/src/main/java/org/elasticsearch/index/get/GetResult.java
index b8c842eefb836..b1dac63c9b8cf 100644
--- a/server/src/main/java/org/elasticsearch/index/get/GetResult.java
+++ b/server/src/main/java/org/elasticsearch/index/get/GetResult.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.index.get;
 
 import org.elasticsearch.ElasticsearchParseException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.compress.CompressorFactory;
@@ -21,7 +20,6 @@
 import org.elasticsearch.common.xcontent.XContentHelper;
 import org.elasticsearch.index.mapper.IgnoredFieldMapper;
 import org.elasticsearch.index.mapper.IgnoredSourceFieldMapper;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.mapper.SourceFieldMapper;
 import org.elasticsearch.search.lookup.Source;
 import org.elasticsearch.xcontent.ToXContentObject;
@@ -61,9 +59,6 @@ public class GetResult implements Writeable, Iterable<DocumentField>, ToXContent
 
     public GetResult(StreamInput in) throws IOException {
         index = in.readString();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readOptionalString();
-        }
         id = in.readString();
         seqNo = in.readZLong();
         primaryTerm = in.readVLong();
@@ -287,9 +282,6 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(index);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeZLong(seqNo);
         out.writeVLong(primaryTerm);
diff --git a/server/src/main/java/org/elasticsearch/index/query/IdsQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/IdsQueryBuilder.java
index fbb905b702293..bb60f31f23e12 100644
--- a/server/src/main/java/org/elasticsearch/index/query/IdsQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/IdsQueryBuilder.java
@@ -11,9 +11,7 @@
 
 import org.apache.lucene.search.Query;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.ParsingException;
-import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.index.mapper.IdFieldMapper;
@@ -25,7 +23,6 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashSet;
 import java.util.Objects;
@@ -55,22 +52,11 @@ public IdsQueryBuilder() {
      */
     public IdsQueryBuilder(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types no longer relevant so ignore
-            String[] types = in.readStringArray();
-            if (types.length > 0) {
-                throw new IllegalStateException("types are no longer supported in ids query but found [" + Arrays.toString(types) + "]");
-            }
-        }
         Collections.addAll(ids, in.readStringArray());
     }
 
     @Override
     protected void doWriteTo(StreamOutput out) throws IOException {
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types not supported so send an empty array to previous versions
-            out.writeStringArray(Strings.EMPTY_ARRAY);
-        }
         out.writeStringCollection(ids);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/index/query/MatchQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/MatchQueryBuilder.java
index 56e002287e1e3..a1f4e14949acd 100644
--- a/server/src/main/java/org/elasticsearch/index/query/MatchQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/MatchQueryBuilder.java
@@ -13,7 +13,6 @@
 import org.apache.lucene.search.FuzzyQuery;
 import org.apache.lucene.search.Query;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -113,10 +112,6 @@ public MatchQueryBuilder(StreamInput in) throws IOException {
         minimumShouldMatch = in.readOptionalString();
         fuzzyRewrite = in.readOptionalString();
         fuzziness = in.readOptionalWriteable(Fuzziness::new);
-        // cutoff_frequency has been removed
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readOptionalFloat();
-        }
         autoGenerateSynonymsPhraseQuery = in.readBoolean();
     }
 
@@ -135,10 +130,6 @@ protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeOptionalString(minimumShouldMatch);
         out.writeOptionalString(fuzzyRewrite);
         out.writeOptionalWriteable(fuzziness);
-        // cutoff_frequency has been removed
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalFloat(null);
-        }
         out.writeBoolean(autoGenerateSynonymsPhraseQuery);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java
index 4b2f4f2517622..a8a3858aabf38 100644
--- a/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/MoreLikeThisQueryBuilder.java
@@ -17,7 +17,6 @@
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.ExceptionsHelper;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.RoutingMissingException;
 import org.elasticsearch.action.termvectors.MultiTermVectorsItemResponse;
 import org.elasticsearch.action.termvectors.MultiTermVectorsRequest;
@@ -201,13 +200,6 @@ public Item(@Nullable String index, XContentBuilder doc) {
         @SuppressWarnings("unchecked")
         Item(StreamInput in) throws IOException {
             index = in.readOptionalString();
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                // types no longer relevant so ignore
-                String type = in.readOptionalString();
-                if (type != null) {
-                    throw new IllegalStateException("types are no longer supported but found [" + type + "]");
-                }
-            }
             if (in.readBoolean()) {
                 doc = (BytesReference) in.readGenericValue();
                 xContentType = in.readEnum(XContentType.class);
@@ -224,10 +216,6 @@ public Item(@Nullable String index, XContentBuilder doc) {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeOptionalString(index);
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                // types not supported so send an empty array to previous versions
-                out.writeOptionalString(null);
-            }
             out.writeBoolean(doc != null);
             if (doc != null) {
                 out.writeGenericValue(doc);
diff --git a/server/src/main/java/org/elasticsearch/index/query/MultiMatchQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/MultiMatchQueryBuilder.java
index df7f28a7a15d5..db072d93cd66a 100644
--- a/server/src/main/java/org/elasticsearch/index/query/MultiMatchQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/MultiMatchQueryBuilder.java
@@ -13,7 +13,6 @@
 import org.apache.lucene.search.Query;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
@@ -222,9 +221,6 @@ public MultiMatchQueryBuilder(StreamInput in) throws IOException {
         fuzzyRewrite = in.readOptionalString();
         tieBreaker = in.readOptionalFloat();
         lenient = in.readOptionalBoolean();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readOptionalFloat();
-        }
         zeroTermsQuery = ZeroTermsQueryOption.readFromStream(in);
         autoGenerateSynonymsPhraseQuery = in.readBoolean();
         fuzzyTranspositions = in.readBoolean();
@@ -245,9 +241,6 @@ protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeOptionalString(fuzzyRewrite);
         out.writeOptionalFloat(tieBreaker);
         out.writeOptionalBoolean(lenient);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalFloat(null);
-        }
         zeroTermsQuery.writeTo(out);
         out.writeBoolean(autoGenerateSynonymsPhraseQuery);
         out.writeBoolean(fuzzyTranspositions);
diff --git a/server/src/main/java/org/elasticsearch/index/shard/IndexingStats.java b/server/src/main/java/org/elasticsearch/index/shard/IndexingStats.java
index 18df167687d90..d6fd81b7de76f 100644
--- a/server/src/main/java/org/elasticsearch/index/shard/IndexingStats.java
+++ b/server/src/main/java/org/elasticsearch/index/shard/IndexingStats.java
@@ -15,13 +15,11 @@
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
 import org.elasticsearch.core.TimeValue;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.ToXContent;
 import org.elasticsearch.xcontent.ToXContentFragment;
 import org.elasticsearch.xcontent.XContentBuilder;
 
 import java.io.IOException;
-import java.util.Map;
 import java.util.Objects;
 import java.util.concurrent.TimeUnit;
 
@@ -400,13 +398,6 @@ public IndexingStats() {
 
     public IndexingStats(StreamInput in) throws IOException {
         totalStats = new Stats(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            if (in.readBoolean()) {
-                Map<String, Stats> typeStats = in.readMap(Stats::new);
-                assert typeStats.size() == 1;
-                assert typeStats.containsKey(MapperService.SINGLE_MAPPING_NAME);
-            }
-        }
     }
 
     public IndexingStats(Stats totalStats) {
@@ -476,8 +467,5 @@ static final class Fields {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         totalStats.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeBoolean(false);
-        }
     }
 }
diff --git a/server/src/main/java/org/elasticsearch/index/translog/Translog.java b/server/src/main/java/org/elasticsearch/index/translog/Translog.java
index 6e83a684cfa82..c53b692fd21e1 100644
--- a/server/src/main/java/org/elasticsearch/index/translog/Translog.java
+++ b/server/src/main/java/org/elasticsearch/index/translog/Translog.java
@@ -1252,9 +1252,7 @@ public long version() {
 
         @Override
         public void writeBody(final StreamOutput out) throws IOException {
-            final int format = out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)
-                ? SERIALIZATION_FORMAT
-                : FORMAT_NO_VERSION_TYPE;
+            final int format = SERIALIZATION_FORMAT;
             out.writeVInt(format);
             out.writeString(id);
             if (format < FORMAT_NO_DOC_TYPE) {
@@ -1421,9 +1419,7 @@ public long version() {
 
         @Override
         public void writeBody(final StreamOutput out) throws IOException {
-            final int format = out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)
-                ? SERIALIZATION_FORMAT
-                : FORMAT_NO_VERSION_TYPE;
+            final int format = SERIALIZATION_FORMAT;
             out.writeVInt(format);
             if (format < FORMAT_NO_DOC_TYPE) {
                 out.writeString(MapperService.SINGLE_MAPPING_NAME);
diff --git a/server/src/main/java/org/elasticsearch/indices/TermsLookup.java b/server/src/main/java/org/elasticsearch/indices/TermsLookup.java
index 0bab521a984e2..75cbed396565b 100644
--- a/server/src/main/java/org/elasticsearch/indices/TermsLookup.java
+++ b/server/src/main/java/org/elasticsearch/indices/TermsLookup.java
@@ -9,11 +9,9 @@
 
 package org.elasticsearch.indices;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.query.TermsQueryBuilder;
 import org.elasticsearch.xcontent.ConstructingObjectParser;
 import org.elasticsearch.xcontent.ParseField;
@@ -55,9 +53,6 @@ public TermsLookup(String index, String id, String path) {
      * Read from a stream.
      */
     public TermsLookup(StreamInput in) throws IOException {
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readOptionalString();
-        }
         id = in.readString();
         path = in.readString();
         index = in.readString();
@@ -66,9 +61,6 @@ public TermsLookup(StreamInput in) throws IOException {
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeString(path);
         out.writeString(index);
diff --git a/server/src/main/java/org/elasticsearch/monitor/os/OsStats.java b/server/src/main/java/org/elasticsearch/monitor/os/OsStats.java
index fe08d30e0dd87..e9a95bba97463 100644
--- a/server/src/main/java/org/elasticsearch/monitor/os/OsStats.java
+++ b/server/src/main/java/org/elasticsearch/monitor/os/OsStats.java
@@ -278,17 +278,13 @@ public Mem(StreamInput in) throws IOException {
                 total = 0;
             }
             this.total = total;
-            if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-                long adjustedTotal = in.readLong();
-                assert adjustedTotal >= 0 : "expected adjusted total memory to be positive, got: " + adjustedTotal;
-                if (adjustedTotal < 0) {
-                    logger.error("negative adjusted total memory [{}] deserialized in memory stats", adjustedTotal);
-                    adjustedTotal = 0;
-                }
-                this.adjustedTotal = adjustedTotal;
-            } else {
-                this.adjustedTotal = total;
+            long adjustedTotal = in.readLong();
+            assert adjustedTotal >= 0 : "expected adjusted total memory to be positive, got: " + adjustedTotal;
+            if (adjustedTotal < 0) {
+                logger.error("negative adjusted total memory [{}] deserialized in memory stats", adjustedTotal);
+                adjustedTotal = 0;
             }
+            this.adjustedTotal = adjustedTotal;
             long free = in.readLong();
             assert free >= 0 : "expected free memory to be positive, got: " + free;
             if (free < 0) {
@@ -301,9 +297,7 @@ public Mem(StreamInput in) throws IOException {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeLong(total);
-            if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-                out.writeLong(adjustedTotal);
-            }
+            out.writeLong(adjustedTotal);
             out.writeLong(free);
         }
 
diff --git a/server/src/main/java/org/elasticsearch/script/ScriptContextStats.java b/server/src/main/java/org/elasticsearch/script/ScriptContextStats.java
index aca4571f6a963..13feb958ae6da 100644
--- a/server/src/main/java/org/elasticsearch/script/ScriptContextStats.java
+++ b/server/src/main/java/org/elasticsearch/script/ScriptContextStats.java
@@ -64,12 +64,9 @@ public static ScriptContextStats read(StreamInput in) throws IOException {
         if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_1_0)) {
             compilationsHistory = new TimeSeries(in);
             cacheEvictionsHistory = new TimeSeries(in);
-        } else if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
+        } else {
             compilationsHistory = new TimeSeries(in).withTotal(compilations);
             cacheEvictionsHistory = new TimeSeries(in).withTotal(cacheEvictions);
-        } else {
-            compilationsHistory = new TimeSeries(compilations);
-            cacheEvictionsHistory = new TimeSeries(cacheEvictions);
         }
         return new ScriptContextStats(
             context,
@@ -99,10 +96,8 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeVLong(compilations);
         out.writeVLong(cacheEvictions);
         out.writeVLong(compilationLimitTriggered);
-        if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            compilationsHistory.writeTo(out);
-            cacheEvictionsHistory.writeTo(out);
-        }
+        compilationsHistory.writeTo(out);
+        cacheEvictionsHistory.writeTo(out);
     }
 
     public String getContext() {
diff --git a/server/src/main/java/org/elasticsearch/search/SearchHit.java b/server/src/main/java/org/elasticsearch/search/SearchHit.java
index 9a8d0bf4ecffd..9a7ad2aa95686 100644
--- a/server/src/main/java/org/elasticsearch/search/SearchHit.java
+++ b/server/src/main/java/org/elasticsearch/search/SearchHit.java
@@ -201,9 +201,6 @@ public static SearchHit readFrom(StreamInput in, boolean pooled) throws IOExcept
             rank = NO_RANK;
         }
         final Text id = in.readOptionalText();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readOptionalText();
-        }
         final NestedIdentity nestedIdentity = in.readOptionalWriteable(NestedIdentity::new);
         final long version = in.readLong();
         final long seqNo = in.readZLong();
@@ -315,9 +312,6 @@ public void writeTo(StreamOutput out) throws IOException {
             throw new IllegalArgumentException("cannot serialize [rank] to version [" + out.getTransportVersion().toReleaseVersion() + "]");
         }
         out.writeOptionalText(id);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalText(SINGLE_MAPPING_TYPE);
-        }
         out.writeOptionalWriteable(nestedIdentity);
         out.writeLong(version);
         out.writeZLong(seqNo);
diff --git a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalBinaryRange.java b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalBinaryRange.java
index 26da58334e16b..d7c788c9a3533 100644
--- a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalBinaryRange.java
+++ b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalBinaryRange.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.search.aggregations.bucket.range;
 
 import org.apache.lucene.util.BytesRef;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.core.Releasables;
@@ -59,9 +58,7 @@ private static String generateKey(BytesRef from, BytesRef to, DocValueFormat for
         }
 
         private static Bucket createFromStream(StreamInput in, DocValueFormat format) throws IOException {
-            // NOTE: the key is required in version == 8.0.0,
-            // while it is optional for all subsequent versions.
-            String key = in.getTransportVersion().equals(TransportVersions.V_8_0_0) ? in.readString() : in.readOptionalString();
+            String key = in.readOptionalString();
             BytesRef from = in.readOptional(StreamInput::readBytesRef);
             BytesRef to = in.readOptional(StreamInput::readBytesRef);
             long docCount = in.readLong();
@@ -72,11 +69,7 @@ private static Bucket createFromStream(StreamInput in, DocValueFormat format) th
 
         @Override
         public void writeTo(StreamOutput out) throws IOException {
-            if (out.getTransportVersion().equals(TransportVersions.V_8_0_0)) {
-                out.writeString(key == null ? generateKey(from, to, format) : key);
-            } else {
-                out.writeOptionalString(key);
-            }
+            out.writeOptionalString(key);
             out.writeOptional(StreamOutput::writeBytesRef, from);
             out.writeOptional(StreamOutput::writeBytesRef, to);
             out.writeLong(docCount);
diff --git a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalRange.java b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalRange.java
index b0ddc3e47354d..01076668674e5 100644
--- a/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalRange.java
+++ b/server/src/main/java/org/elasticsearch/search/aggregations/bucket/range/InternalRange.java
@@ -8,7 +8,6 @@
  */
 package org.elasticsearch.search.aggregations.bucket.range;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.core.Releasables;
@@ -138,13 +137,7 @@ private static String generateKey(double from, double to, DocValueFormat format)
 
         @Override
         public void writeTo(StreamOutput out) throws IOException {
-            // NOTE: the key is required in version == 8.0.0,
-            // while it is optional for all subsequent versions.
-            if (out.getTransportVersion().equals(TransportVersions.V_8_0_0)) {
-                out.writeString(key == null ? generateKey(from, to, format) : key);
-            } else {
-                out.writeOptionalString(key);
-            }
+            out.writeOptionalString(key);
             out.writeDouble(from);
             out.writeOptionalDouble(from);
             out.writeDouble(to);
@@ -230,9 +223,7 @@ public InternalRange(StreamInput in) throws IOException {
         int size = in.readVInt();
         List<B> ranges = new ArrayList<>(size);
         for (int i = 0; i < size; i++) {
-            // NOTE: the key is required in version == 8.0.0,
-            // while it is optional for all subsequent versions.
-            final String key = in.getTransportVersion().equals(TransportVersions.V_8_0_0) ? in.readString() : in.readOptionalString();
+            final String key = in.readOptionalString();
             double from = in.readDouble();
             final Double originalFrom = in.readOptionalDouble();
             if (originalFrom != null) {
diff --git a/server/src/main/java/org/elasticsearch/search/internal/ShardSearchRequest.java b/server/src/main/java/org/elasticsearch/search/internal/ShardSearchRequest.java
index 10d2fb0e23b3b..48e2c55965ab6 100644
--- a/server/src/main/java/org/elasticsearch/search/internal/ShardSearchRequest.java
+++ b/server/src/main/java/org/elasticsearch/search/internal/ShardSearchRequest.java
@@ -20,7 +20,6 @@
 import org.elasticsearch.cluster.metadata.AliasMetadata;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.common.CheckedBiConsumer;
-import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.hash.MessageDigests;
@@ -55,7 +54,6 @@
 
 import java.io.IOException;
 import java.util.ArrayList;
-import java.util.Arrays;
 import java.util.List;
 import java.util.Map;
 
@@ -306,15 +304,6 @@ public ShardSearchRequest(StreamInput in) throws IOException {
                 source.subSearches(subSearchSourceBuilders);
             }
         }
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types no longer relevant so ignore
-            String[] types = in.readStringArray();
-            if (types.length > 0) {
-                throw new IllegalStateException(
-                    "types are no longer supported in search requests but found [" + Arrays.toString(types) + "]"
-                );
-            }
-        }
         aliasFilter = AliasFilter.readFrom(in);
         indexBoost = in.readFloat();
         nowInMillis = in.readVLong();
@@ -371,10 +360,6 @@ protected final void innerWriteTo(StreamOutput out, boolean asKey) throws IOExce
             }
             out.writeNamedWriteableCollection(rankQueryBuilders);
         }
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            // types not supported so send an empty array to previous versions
-            out.writeStringArray(Strings.EMPTY_ARRAY);
-        }
         aliasFilter.writeTo(out);
         out.writeFloat(indexBoost);
         if (asKey == false) {
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 d703eaed1dc95..422a99e7d72f5 100644
--- a/server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/sort/GeoDistanceSortBuilder.java
@@ -21,7 +21,6 @@
 import org.apache.lucene.util.BitSet;
 import org.elasticsearch.ElasticsearchParseException;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.geo.GeoDistance;
 import org.elasticsearch.common.geo.GeoPoint;
@@ -40,7 +39,6 @@
 import org.elasticsearch.index.fielddata.plain.LatLonPointIndexFieldData;
 import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.query.GeoValidationMethod;
-import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryRewriteContext;
 import org.elasticsearch.index.query.SearchExecutionContext;
 import org.elasticsearch.search.DocValueFormat;
@@ -163,14 +161,6 @@ public GeoDistanceSortBuilder(StreamInput in) throws IOException {
         unit = DistanceUnit.readFromStream(in);
         order = SortOrder.readFromStream(in);
         sortMode = in.readOptionalWriteable(SortMode::readFromStream);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            if (in.readOptionalNamedWriteable(QueryBuilder.class) != null || in.readOptionalString() != null) {
-                throw new IOException(
-                    "the [sort] options [nested_path] and [nested_filter] are removed in 8.x, " + "please use [nested] instead"
-                );
-            }
-
-        }
         nestedSort = in.readOptionalWriteable(NestedSortBuilder::new);
         validation = GeoValidationMethod.readFromStream(in);
         ignoreUnmapped = in.readBoolean();
@@ -184,10 +174,6 @@ public void writeTo(StreamOutput out) throws IOException {
         unit.writeTo(out);
         order.writeTo(out);
         out.writeOptionalWriteable(sortMode);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalNamedWriteable(null);
-            out.writeOptionalString(null);
-        }
         out.writeOptionalWriteable(nestedSort);
         validation.writeTo(out);
         out.writeBoolean(ignoreUnmapped);
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 106b483790fe3..a8a06008c3971 100644
--- a/server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/sort/ScriptSortBuilder.java
@@ -16,7 +16,6 @@
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.BytesRefBuilder;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -32,7 +31,6 @@
 import org.elasticsearch.index.fielddata.fieldcomparator.BytesRefFieldComparatorSource;
 import org.elasticsearch.index.fielddata.fieldcomparator.DoubleValuesComparatorSource;
 import org.elasticsearch.index.mapper.MappedFieldType;
-import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryRewriteContext;
 import org.elasticsearch.index.query.QueryShardException;
 import org.elasticsearch.index.query.SearchExecutionContext;
@@ -112,13 +110,6 @@ public ScriptSortBuilder(StreamInput in) throws IOException {
         type = ScriptSortType.readFromStream(in);
         order = SortOrder.readFromStream(in);
         sortMode = in.readOptionalWriteable(SortMode::readFromStream);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            if (in.readOptionalNamedWriteable(QueryBuilder.class) != null || in.readOptionalString() != null) {
-                throw new IOException(
-                    "the [sort] options [nested_path] and [nested_filter] are removed in 8.x, " + "please use [nested] instead"
-                );
-            }
-        }
         nestedSort = in.readOptionalWriteable(NestedSortBuilder::new);
     }
 
@@ -128,10 +119,6 @@ public void writeTo(StreamOutput out) throws IOException {
         type.writeTo(out);
         order.writeTo(out);
         out.writeOptionalWriteable(sortMode);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalString(null);
-            out.writeOptionalNamedWriteable(null);
-        }
         out.writeOptionalWriteable(nestedSort);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/search/vectors/KnnVectorQueryBuilder.java b/server/src/main/java/org/elasticsearch/search/vectors/KnnVectorQueryBuilder.java
index 1139e0c3119fb..585410deb84de 100644
--- a/server/src/main/java/org/elasticsearch/search/vectors/KnnVectorQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/vectors/KnnVectorQueryBuilder.java
@@ -691,6 +691,6 @@ protected boolean doEquals(KnnVectorQueryBuilder other) {
 
     @Override
     public TransportVersion getMinimalSupportedVersion() {
-        return TransportVersions.V_8_0_0;
+        return TransportVersion.minimumCompatible();
     }
 }
diff --git a/server/src/main/java/org/elasticsearch/transport/Header.java b/server/src/main/java/org/elasticsearch/transport/Header.java
index 468bdb6e58e9f..148612b9554fe 100644
--- a/server/src/main/java/org/elasticsearch/transport/Header.java
+++ b/server/src/main/java/org/elasticsearch/transport/Header.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.transport;
 
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.util.concurrent.ThreadContext;
 import org.elasticsearch.core.Tuple;
@@ -96,10 +95,6 @@ void finishParsingHeader(StreamInput input) throws IOException {
         this.headers = ThreadContext.readHeadersFromStream(input);
 
         if (isRequest()) {
-            if (version.before(TransportVersions.V_8_0_0)) {
-                // discard features
-                input.readStringArray();
-            }
             this.actionName = input.readString();
         } else {
             this.actionName = RESPONSE_NAME;
diff --git a/server/src/main/java/org/elasticsearch/transport/OutboundHandler.java b/server/src/main/java/org/elasticsearch/transport/OutboundHandler.java
index 5243d371ae96c..2db3b56b60d38 100644
--- a/server/src/main/java/org/elasticsearch/transport/OutboundHandler.java
+++ b/server/src/main/java/org/elasticsearch/transport/OutboundHandler.java
@@ -14,7 +14,6 @@
 import org.apache.logging.log4j.Logger;
 import org.apache.lucene.util.BytesRef;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.cluster.node.DiscoveryNode;
 import org.elasticsearch.common.Strings;
@@ -298,10 +297,6 @@ public static BytesReference serialize(
         byteStreamOutput.skip(TcpHeader.HEADER_SIZE);
         threadContext.writeTo(byteStreamOutput);
         if (messageDirection == MessageDirection.REQUEST) {
-            if (version.before(TransportVersions.V_8_0_0)) {
-                // empty features array
-                byteStreamOutput.writeStringArray(Strings.EMPTY_ARRAY);
-            }
             byteStreamOutput.writeString(action);
         }
 
diff --git a/server/src/main/java/org/elasticsearch/transport/TransportLogger.java b/server/src/main/java/org/elasticsearch/transport/TransportLogger.java
index 17338289a15fa..56338808deae2 100644
--- a/server/src/main/java/org/elasticsearch/transport/TransportLogger.java
+++ b/server/src/main/java/org/elasticsearch/transport/TransportLogger.java
@@ -11,7 +11,6 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.util.concurrent.ThreadContext;
@@ -90,10 +89,6 @@ private static String format(TcpChannel channel, BytesReference message, String
                 ThreadContext.readHeadersFromStream(streamInput);
 
                 if (isRequest) {
-                    if (version.before(TransportVersions.V_8_0_0)) {
-                        // discard features
-                        streamInput.readStringArray();
-                    }
                     sb.append(", action: ").append(streamInput.readString());
                 }
                 sb.append(']');