diff --git a/server/src/main/java/org/elasticsearch/action/DocWriteResponse.java b/server/src/main/java/org/elasticsearch/action/DocWriteResponse.java
index d47469ddf10d9..da367e50a0d03 100644
--- a/server/src/main/java/org/elasticsearch/action/DocWriteResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/DocWriteResponse.java
@@ -8,7 +8,6 @@
  */
 package org.elasticsearch.action;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.bulk.IndexDocFailureStoreStatus;
 import org.elasticsearch.action.support.WriteRequest;
 import org.elasticsearch.action.support.WriteRequest.RefreshPolicy;
@@ -115,10 +114,6 @@ public DocWriteResponse(ShardId shardId, String id, long seqNo, long primaryTerm
     protected DocWriteResponse(ShardId shardId, StreamInput in) throws IOException {
         super(in);
         this.shardId = shardId;
-        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();
         version = in.readZLong();
         seqNo = in.readZLong();
@@ -134,10 +129,6 @@ protected DocWriteResponse(ShardId shardId, StreamInput in) throws IOException {
     protected DocWriteResponse(StreamInput in) throws IOException {
         super(in);
         shardId = new ShardId(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();
         version = in.readZLong();
         seqNo = in.readZLong();
@@ -266,9 +257,6 @@ public void writeTo(StreamOutput out) throws IOException {
     }
 
     private void writeWithoutShardId(StreamOutput out) throws IOException {
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeZLong(version);
         out.writeZLong(seqNo);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequest.java b/server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequest.java
index ed25f6d531f52..c3d697edcb699 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/cluster/configuration/AddVotingConfigExclusionsRequest.java
@@ -8,7 +8,6 @@
  */
 package org.elasticsearch.action.admin.cluster.configuration;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.support.master.MasterNodeRequest;
 import org.elasticsearch.cluster.ClusterState;
@@ -78,12 +77,6 @@ public AddVotingConfigExclusionsRequest(TimeValue masterNodeTimeout, String[] no
 
     public AddVotingConfigExclusionsRequest(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            final String[] legacyNodeDescriptions = in.readStringArray();
-            if (legacyNodeDescriptions.length > 0) {
-                throw new IllegalArgumentException("legacy [node_name] field was deprecated and must be empty");
-            }
-        }
         nodeIds = in.readStringArray();
         nodeNames = in.readStringArray();
         timeout = in.readTimeValue();
@@ -191,9 +184,6 @@ public ActionRequestValidationException validate() {
     @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(nodeIds);
         out.writeStringArray(nodeNames);
         out.writeTimeValue(timeout);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/create/CreateSnapshotRequest.java b/server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/create/CreateSnapshotRequest.java
index 5637971665a0c..134d120187c3c 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/create/CreateSnapshotRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/create/CreateSnapshotRequest.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.action.admin.cluster.snapshots.create;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.TransportVersion;
 import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.IndicesRequest;
@@ -21,7 +20,6 @@
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
-import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.core.Nullable;
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.xcontent.ToXContentObject;
@@ -36,7 +34,6 @@
 
 import static org.elasticsearch.action.ValidateActions.addValidationError;
 import static org.elasticsearch.common.Strings.EMPTY_ARRAY;
-import static org.elasticsearch.common.settings.Settings.readSettingsFromStream;
 import static org.elasticsearch.common.xcontent.support.XContentMapValues.nodeBooleanValue;
 
 /**
@@ -58,8 +55,6 @@ public class CreateSnapshotRequest extends MasterNodeRequest<CreateSnapshotReque
         IndicesRequest.Replaceable,
         ToXContentObject {
 
-    public static final TransportVersion SETTINGS_IN_REQUEST_VERSION = TransportVersions.V_8_0_0;
-
     public static final int MAXIMUM_METADATA_BYTES = 1024; // chosen arbitrarily
 
     private String snapshot;
@@ -107,9 +102,6 @@ public CreateSnapshotRequest(StreamInput in) throws IOException {
         repository = in.readString();
         indices = in.readStringArray();
         indicesOptions = IndicesOptions.readIndicesOptions(in);
-        if (in.getTransportVersion().before(SETTINGS_IN_REQUEST_VERSION)) {
-            readSettingsFromStream(in);
-        }
         featureStates = in.readStringArray();
         includeGlobalState = in.readBoolean();
         waitForCompletion = in.readBoolean();
@@ -125,9 +117,6 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeString(repository);
         out.writeStringArray(indices);
         indicesOptions.writeIndicesOptions(out);
-        if (out.getTransportVersion().before(SETTINGS_IN_REQUEST_VERSION)) {
-            Settings.EMPTY.writeTo(out);
-        }
         out.writeStringArray(featureStates);
         out.writeBoolean(includeGlobalState);
         out.writeBoolean(waitForCompletion);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java
index f191ab3827347..813a42b9d6730 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/create/CreateIndexRequest.java
@@ -87,19 +87,7 @@ public CreateIndexRequest(StreamInput in) throws IOException {
         cause = in.readString();
         index = in.readString();
         settings = readSettingsFromStream(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            int size = in.readVInt();
-            assert size <= 1 : "Expected to read 0 or 1 mappings, but received " + size;
-            if (size == 1) {
-                String type = in.readString();
-                if (MapperService.SINGLE_MAPPING_NAME.equals(type) == false) {
-                    throw new IllegalArgumentException("Expected to receive mapping type of [_doc] but got [" + type + "]");
-                }
-                mappings = in.readString();
-            }
-        } else {
-            mappings = in.readString();
-        }
+        mappings = in.readString();
         int aliasesSize = in.readVInt();
         for (int i = 0; i < aliasesSize; i++) {
             aliases.add(new Alias(in));
@@ -510,17 +498,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeString(cause);
         out.writeString(index);
         settings.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            if ("{}".equals(mappings)) {
-                out.writeVInt(0);
-            } else {
-                out.writeVInt(1);
-                out.writeString(MapperService.SINGLE_MAPPING_NAME);
-                out.writeString(mappings);
-            }
-        } else {
-            out.writeString(mappings);
-        }
+        out.writeString(mappings);
         out.writeCollection(aliases);
         waitForActiveShards.writeTo(out);
         out.writeString(origin);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/forcemerge/ForceMergeRequest.java b/server/src/main/java/org/elasticsearch/action/admin/indices/forcemerge/ForceMergeRequest.java
index 3a3b25f1c05de..a5d353b91334d 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/forcemerge/ForceMergeRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/forcemerge/ForceMergeRequest.java
@@ -9,8 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.forcemerge;
 
-import org.elasticsearch.TransportVersion;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.support.broadcast.BroadcastRequest;
 import org.elasticsearch.common.UUIDs;
@@ -48,8 +46,6 @@ public static final class Defaults {
      */
     private boolean shouldStoreResult;
 
-    private static final TransportVersion FORCE_MERGE_UUID_SIMPLE_VERSION = TransportVersions.V_8_0_0;
-
     /**
      * Force merge UUID to store in the live commit data of a shard under
      * {@link org.elasticsearch.index.engine.Engine#FORCE_MERGE_UUID_KEY} after force merging it.
@@ -71,12 +67,7 @@ public ForceMergeRequest(StreamInput in) throws IOException {
         maxNumSegments = in.readInt();
         onlyExpungeDeletes = in.readBoolean();
         flush = in.readBoolean();
-        if (in.getTransportVersion().onOrAfter(FORCE_MERGE_UUID_SIMPLE_VERSION)) {
-            forceMergeUUID = in.readString();
-        } else {
-            forceMergeUUID = in.readOptionalString();
-            assert forceMergeUUID != null : "optional was just used as a BwC measure";
-        }
+        forceMergeUUID = in.readString();
     }
 
     /**
@@ -167,11 +158,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeInt(maxNumSegments);
         out.writeBoolean(onlyExpungeDeletes);
         out.writeBoolean(flush);
-        if (out.getTransportVersion().onOrAfter(FORCE_MERGE_UUID_SIMPLE_VERSION)) {
-            out.writeString(forceMergeUUID);
-        } else {
-            out.writeOptionalString(forceMergeUUID);
-        }
+        out.writeString(forceMergeUUID);
     }
 
     @Override
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStats.java b/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStats.java
index 1351674fffbfa..0fba9bdcd0a92 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStats.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStats.java
@@ -217,9 +217,7 @@ public CommonStats(StreamInput in) throws IOException {
         translog = in.readOptionalWriteable(TranslogStats::new);
         requestCache = in.readOptionalWriteable(RequestCacheStats::new);
         recoveryStats = in.readOptionalWriteable(RecoveryStats::new);
-        if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            bulk = in.readOptionalWriteable(BulkStats::new);
-        }
+        bulk = in.readOptionalWriteable(BulkStats::new);
         shards = in.readOptionalWriteable(ShardCountStats::new);
         if (in.getTransportVersion().onOrAfter(VERSION_SUPPORTING_NODE_MAPPINGS)) {
             nodeMappings = in.readOptionalWriteable(NodeMappingStats::new);
@@ -250,9 +248,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalWriteable(translog);
         out.writeOptionalWriteable(requestCache);
         out.writeOptionalWriteable(recoveryStats);
-        if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            out.writeOptionalWriteable(bulk);
-        }
+        out.writeOptionalWriteable(bulk);
         out.writeOptionalWriteable(shards);
         if (out.getTransportVersion().onOrAfter(VERSION_SUPPORTING_NODE_MAPPINGS)) {
             out.writeOptionalWriteable(nodeMappings);
diff --git a/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStatsFlags.java b/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStatsFlags.java
index ae6e1985d56c7..c3fb6cc4eb18e 100644
--- a/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStatsFlags.java
+++ b/server/src/main/java/org/elasticsearch/action/admin/indices/stats/CommonStatsFlags.java
@@ -9,8 +9,6 @@
 
 package org.elasticsearch.action.admin.indices.stats;
 
-import org.elasticsearch.TransportVersions;
-import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -56,9 +54,6 @@ public CommonStatsFlags(StreamInput in) throws IOException {
                 flags.add(flag);
             }
         }
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readStringArray();
-        }
         groups = in.readStringArray();
         fieldDataFields = in.readStringArray();
         completionDataFields = in.readStringArray();
@@ -73,10 +68,6 @@ public void writeTo(StreamOutput out) throws IOException {
             longFlags |= (1 << flag.getIndex());
         }
         out.writeLong(longFlags);
-
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeStringArrayNullable(Strings.EMPTY_ARRAY);
-        }
         out.writeStringArrayNullable(groups);
         out.writeStringArrayNullable(fieldDataFields);
         out.writeStringArrayNullable(completionDataFields);
diff --git a/server/src/main/java/org/elasticsearch/action/bulk/BulkItemResponse.java b/server/src/main/java/org/elasticsearch/action/bulk/BulkItemResponse.java
index 1ff970de7525e..68677bbfd10e4 100644
--- a/server/src/main/java/org/elasticsearch/action/bulk/BulkItemResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/bulk/BulkItemResponse.java
@@ -22,7 +22,6 @@
 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.seqno.SequenceNumbers;
 import org.elasticsearch.index.shard.ShardId;
 import org.elasticsearch.rest.RestStatus;
@@ -189,11 +188,6 @@ private Failure(
          */
         public Failure(StreamInput in) throws IOException {
             index = in.readString();
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                in.readString();
-                // can't make an assertion about type names here because too many tests still set their own
-                // types bypassing various checks
-            }
             id = in.readOptionalString();
             cause = in.readException();
             status = ExceptionsHelper.status(cause);
@@ -210,9 +204,6 @@ public Failure(StreamInput in) throws IOException {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeString(index);
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                out.writeString(MapperService.SINGLE_MAPPING_NAME);
-            }
             out.writeOptionalString(id);
             out.writeException(cause);
             out.writeZLong(seqNo);
diff --git a/server/src/main/java/org/elasticsearch/action/delete/DeleteRequest.java b/server/src/main/java/org/elasticsearch/action/delete/DeleteRequest.java
index 1a5495412f605..38370563cb160 100644
--- a/server/src/main/java/org/elasticsearch/action/delete/DeleteRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/delete/DeleteRequest.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.action.delete;
 
 import org.apache.lucene.util.RamUsageEstimator;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.CompositeIndicesRequest;
 import org.elasticsearch.action.DocWriteRequest;
@@ -22,7 +21,6 @@
 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.shard.ShardId;
 
 import java.io.IOException;
@@ -63,10 +61,6 @@ public DeleteRequest(StreamInput in) throws IOException {
 
     public DeleteRequest(@Nullable ShardId shardId, StreamInput in) throws IOException {
         super(shardId, 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();
         version = in.readLong();
@@ -255,9 +249,6 @@ public void writeThin(StreamOutput out) throws IOException {
     }
 
     private void writeBody(StreamOutput out) throws IOException {
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeOptionalString(routing());
         out.writeLong(version);
diff --git a/server/src/main/java/org/elasticsearch/action/explain/ExplainRequest.java b/server/src/main/java/org/elasticsearch/action/explain/ExplainRequest.java
index 91dbe32feca39..d55106c884135 100644
--- a/server/src/main/java/org/elasticsearch/action/explain/ExplainRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/explain/ExplainRequest.java
@@ -9,14 +9,12 @@
 
 package org.elasticsearch.action.explain;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionRequestValidationException;
 import org.elasticsearch.action.ValidateActions;
 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;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.search.fetch.subphase.FetchSourceContext;
 import org.elasticsearch.search.internal.AliasFilter;
@@ -55,10 +53,6 @@ public ExplainRequest(String index, String id) {
 
     ExplainRequest(StreamInput in) throws IOException {
         super(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            String type = in.readString();
-            assert MapperService.SINGLE_MAPPING_NAME.equals(type);
-        }
         id = in.readString();
         routing = in.readOptionalString();
         preference = in.readOptionalString();
@@ -161,9 +155,6 @@ public ActionRequestValidationException validate() {
     @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/explain/ExplainResponse.java b/server/src/main/java/org/elasticsearch/action/explain/ExplainResponse.java
index 8155cc5d041c5..ebbc649612ba3 100644
--- a/server/src/main/java/org/elasticsearch/action/explain/ExplainResponse.java
+++ b/server/src/main/java/org/elasticsearch/action/explain/ExplainResponse.java
@@ -10,12 +10,10 @@
 package org.elasticsearch.action.explain;
 
 import org.apache.lucene.search.Explanation;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionResponse;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.index.get.GetResult;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.ToXContentObject;
@@ -65,9 +63,6 @@ public ExplainResponse(String index, String id, boolean exists, Explanation expl
 
     public ExplainResponse(StreamInput in) throws IOException {
         index = in.readString();
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readString();
-        }
         id = in.readString();
         exists = in.readBoolean();
         if (in.readBoolean()) {
@@ -113,9 +108,6 @@ public RestStatus status() {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(index);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeString(MapperService.SINGLE_MAPPING_NAME);
-        }
         out.writeString(id);
         out.writeBoolean(exists);
         if (explanation == null) {
diff --git a/server/src/main/java/org/elasticsearch/action/fieldcaps/FieldCapabilities.java b/server/src/main/java/org/elasticsearch/action/fieldcaps/FieldCapabilities.java
index d0d1739860634..48dc58e3ae9c4 100644
--- a/server/src/main/java/org/elasticsearch/action/fieldcaps/FieldCapabilities.java
+++ b/server/src/main/java/org/elasticsearch/action/fieldcaps/FieldCapabilities.java
@@ -9,7 +9,6 @@
 
 package org.elasticsearch.action.fieldcaps;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -229,23 +228,13 @@ public FieldCapabilities(
         this.isMetadataField = in.readBoolean();
         this.isSearchable = in.readBoolean();
         this.isAggregatable = in.readBoolean();
-        if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            this.isDimension = in.readBoolean();
-            this.metricType = in.readOptionalEnum(TimeSeriesParams.MetricType.class);
-        } else {
-            this.isDimension = false;
-            this.metricType = null;
-        }
+        this.isDimension = in.readBoolean();
+        this.metricType = in.readOptionalEnum(TimeSeriesParams.MetricType.class);
         this.indices = in.readOptionalStringArray();
         this.nonSearchableIndices = in.readOptionalStringArray();
         this.nonAggregatableIndices = in.readOptionalStringArray();
-        if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            this.nonDimensionIndices = in.readOptionalStringArray();
-            this.metricConflictsIndices = in.readOptionalStringArray();
-        } else {
-            this.nonDimensionIndices = null;
-            this.metricConflictsIndices = null;
-        }
+        this.nonDimensionIndices = in.readOptionalStringArray();
+        this.metricConflictsIndices = in.readOptionalStringArray();
         meta = in.readMap(i -> i.readCollectionAsSet(StreamInput::readString));
     }
 
@@ -256,17 +245,13 @@ 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.writeOptionalStringArray(indices);
         out.writeOptionalStringArray(nonSearchableIndices);
         out.writeOptionalStringArray(nonAggregatableIndices);
-        if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            out.writeOptionalStringArray(nonDimensionIndices);
-            out.writeOptionalStringArray(metricConflictsIndices);
-        }
+        out.writeOptionalStringArray(nonDimensionIndices);
+        out.writeOptionalStringArray(metricConflictsIndices);
         out.writeMap(meta, StreamOutput::writeStringCollection);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/action/search/CanMatchNodeRequest.java b/server/src/main/java/org/elasticsearch/action/search/CanMatchNodeRequest.java
index 93a9e4d87f29f..eaba7b9c762c6 100644
--- a/server/src/main/java/org/elasticsearch/action/search/CanMatchNodeRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/search/CanMatchNodeRequest.java
@@ -9,11 +9,9 @@
 
 package org.elasticsearch.action.search;
 
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.IndicesRequest;
 import org.elasticsearch.action.OriginalIndices;
 import org.elasticsearch.action.support.IndicesOptions;
-import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.io.stream.StreamOutput;
 import org.elasticsearch.common.io.stream.Writeable;
@@ -186,15 +184,6 @@ public CanMatchNodeRequest(StreamInput in) throws IOException {
         source = in.readOptionalWriteable(SearchSourceBuilder::new);
         indicesOptions = IndicesOptions.readIndicesOptions(in);
         searchType = SearchType.fromId(in.readByte());
-        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) + "]"
-                );
-            }
-        }
         scroll = in.readOptionalTimeValue();
         requestCache = in.readOptionalBoolean();
         allowPartialSearchResults = in.readBoolean();
@@ -212,10 +201,6 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeOptionalWriteable(source);
         indicesOptions.writeIndicesOptions(out);
         out.writeByte(searchType.id());
-        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.writeOptionalTimeValue(scroll);
         out.writeOptionalBoolean(requestCache);
         out.writeBoolean(allowPartialSearchResults);
diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/ComposableIndexTemplate.java b/server/src/main/java/org/elasticsearch/cluster/metadata/ComposableIndexTemplate.java
index 95736eabc234a..ffc618227e018 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/ComposableIndexTemplate.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/ComposableIndexTemplate.java
@@ -546,11 +546,7 @@ public DataStreamTemplate(boolean hidden, boolean allowCustomRouting) {
 
         DataStreamTemplate(StreamInput in) throws IOException {
             hidden = in.readBoolean();
-            if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-                allowCustomRouting = in.readBoolean();
-            } else {
-                allowCustomRouting = false;
-            }
+            allowCustomRouting = in.readBoolean();
             if (in.getTransportVersion().between(TransportVersions.V_8_1_0, TransportVersions.V_8_3_0)) {
                 // Accidentally included index_mode to binary node to node protocol in previous releases.
                 // (index_mode is removed and was part of code based when tsdb was behind a feature flag)
@@ -594,9 +590,7 @@ public boolean isAllowCustomRouting() {
         @Override
         public void writeTo(StreamOutput out) throws IOException {
             out.writeBoolean(hidden);
-            if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-                out.writeBoolean(allowCustomRouting);
-            }
+            out.writeBoolean(allowCustomRouting);
             if (out.getTransportVersion().between(TransportVersions.V_8_1_0, TransportVersions.V_8_3_0)) {
                 // See comment in constructor.
                 out.writeBoolean(false);
diff --git a/server/src/main/java/org/elasticsearch/cluster/metadata/DataStream.java b/server/src/main/java/org/elasticsearch/cluster/metadata/DataStream.java
index 3da6b137ccdc9..9e7fcb1e60f16 100644
--- a/server/src/main/java/org/elasticsearch/cluster/metadata/DataStream.java
+++ b/server/src/main/java/org/elasticsearch/cluster/metadata/DataStream.java
@@ -299,7 +299,7 @@ public static DataStream read(StreamInput in) throws IOException {
         var hidden = in.readBoolean();
         var replicated = in.readBoolean();
         var system = in.readBoolean();
-        var allowCustomRouting = in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0) ? in.readBoolean() : false;
+        var allowCustomRouting = in.readBoolean();
         var indexMode = in.getTransportVersion().onOrAfter(TransportVersions.V_8_1_0) ? in.readOptionalEnum(IndexMode.class) : null;
         var lifecycle = in.getTransportVersion().onOrAfter(TransportVersions.V_8_9_X)
             ? in.readOptionalWriteable(DataStreamLifecycle::new)
@@ -1449,9 +1449,7 @@ public void writeTo(StreamOutput out) throws IOException {
         out.writeBoolean(hidden);
         out.writeBoolean(replicated);
         out.writeBoolean(system);
-        if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            out.writeBoolean(allowCustomRouting);
-        }
+        out.writeBoolean(allowCustomRouting);
         if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_1_0)) {
             out.writeOptionalEnum(indexMode);
         }
diff --git a/server/src/main/java/org/elasticsearch/common/compress/CompressedXContent.java b/server/src/main/java/org/elasticsearch/common/compress/CompressedXContent.java
index e50b267dbc1a9..8aafce8215ceb 100644
--- a/server/src/main/java/org/elasticsearch/common/compress/CompressedXContent.java
+++ b/server/src/main/java/org/elasticsearch/common/compress/CompressedXContent.java
@@ -10,7 +10,6 @@
 package org.elasticsearch.common.compress;
 
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.bytes.BytesReference;
 import org.elasticsearch.common.hash.MessageDigests;
@@ -202,27 +201,14 @@ public String getSha256() {
     }
 
     public static CompressedXContent readCompressedString(StreamInput in) throws IOException {
-        final String sha256;
-        final byte[] compressedData;
-        if (in.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            sha256 = in.readString();
-            compressedData = in.readByteArray();
-        } else {
-            int crc32 = in.readInt();
-            compressedData = in.readByteArray();
-            sha256 = sha256FromCompressed(compressedData);
-        }
+        String sha256 = in.readString();
+        byte[] compressedData = in.readByteArray();
         return new CompressedXContent(compressedData, sha256);
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        if (out.getTransportVersion().onOrAfter(TransportVersions.V_8_0_0)) {
-            out.writeString(sha256);
-        } else {
-            int crc32 = crc32FromCompressed(bytes);
-            out.writeInt(crc32);
-        }
+        out.writeString(sha256);
         out.writeByteArray(bytes);
     }
 
diff --git a/server/src/main/java/org/elasticsearch/index/query/AbstractGeometryQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/AbstractGeometryQueryBuilder.java
index b2a816c9e5690..51f90f9decfa0 100644
--- a/server/src/main/java/org/elasticsearch/index/query/AbstractGeometryQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/AbstractGeometryQueryBuilder.java
@@ -12,7 +12,6 @@
 import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.SetOnce;
-import org.elasticsearch.TransportVersions;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.get.GetRequest;
 import org.elasticsearch.client.internal.Client;
@@ -29,7 +28,6 @@
 import org.elasticsearch.geometry.GeometryCollection;
 import org.elasticsearch.geometry.ShapeType;
 import org.elasticsearch.index.mapper.MappedFieldType;
-import org.elasticsearch.index.mapper.MapperService;
 import org.elasticsearch.xcontent.NamedXContentRegistry;
 import org.elasticsearch.xcontent.ParseField;
 import org.elasticsearch.xcontent.XContentBuilder;
@@ -152,10 +150,6 @@ protected AbstractGeometryQueryBuilder(StreamInput in) throws IOException {
         } else {
             shape = null;
             indexedShapeId = in.readOptionalString();
-            if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                String type = in.readOptionalString();
-                assert MapperService.SINGLE_MAPPING_NAME.equals(type) : "Expected type [_doc], got [" + type + "]";
-            }
             indexedShapeIndex = in.readOptionalString();
             indexedShapePath = in.readOptionalString();
             indexedShapeRouting = in.readOptionalString();
@@ -177,9 +171,6 @@ protected void doWriteTo(StreamOutput out) throws IOException {
             GeometryIO.writeGeometry(out, shape);
         } else {
             out.writeOptionalString(indexedShapeId);
-            if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-                out.writeOptionalString(MapperService.SINGLE_MAPPING_NAME);
-            }
             out.writeOptionalString(indexedShapeIndex);
             out.writeOptionalString(indexedShapePath);
             out.writeOptionalString(indexedShapeRouting);
diff --git a/server/src/main/java/org/elasticsearch/index/query/GeoBoundingBoxQueryBuilder.java b/server/src/main/java/org/elasticsearch/index/query/GeoBoundingBoxQueryBuilder.java
index 254f70aeaeba2..aaec018f67954 100644
--- a/server/src/main/java/org/elasticsearch/index/query/GeoBoundingBoxQueryBuilder.java
+++ b/server/src/main/java/org/elasticsearch/index/query/GeoBoundingBoxQueryBuilder.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.Numbers;
 import org.elasticsearch.common.ParsingException;
 import org.elasticsearch.common.geo.GeoBoundingBox;
@@ -78,9 +77,6 @@ public GeoBoundingBoxQueryBuilder(StreamInput in) throws IOException {
         super(in);
         fieldName = in.readString();
         geoBoundingBox = new GeoBoundingBox(in);
-        if (in.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            in.readVInt(); // ignore value
-        }
         validationMethod = GeoValidationMethod.readFromStream(in);
         ignoreUnmapped = in.readBoolean();
     }
@@ -89,9 +85,6 @@ public GeoBoundingBoxQueryBuilder(StreamInput in) throws IOException {
     protected void doWriteTo(StreamOutput out) throws IOException {
         out.writeString(fieldName);
         geoBoundingBox.writeTo(out);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeVInt(0);
-        }
         validationMethod.writeTo(out);
         out.writeBoolean(ignoreUnmapped);
     }
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 2d36d28b85e42..89250fd8f3f68 100644
--- a/server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java
+++ b/server/src/main/java/org/elasticsearch/search/sort/FieldSortBuilder.java
@@ -17,7 +17,6 @@
 import org.apache.lucene.search.SortField;
 import org.elasticsearch.ElasticsearchParseException;
 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.time.DateMathParser;
@@ -34,7 +33,6 @@
 import org.elasticsearch.index.mapper.NestedLookup;
 import org.elasticsearch.index.mapper.NestedObjectMapper;
 import org.elasticsearch.index.mapper.NumberFieldMapper.NumberFieldType;
-import org.elasticsearch.index.query.QueryBuilder;
 import org.elasticsearch.index.query.QueryRewriteContext;
 import org.elasticsearch.index.query.QueryShardException;
 import org.elasticsearch.index.query.SearchExecutionContext;
@@ -134,13 +132,6 @@ public FieldSortBuilder(String fieldName) {
      */
     public FieldSortBuilder(StreamInput in) throws IOException {
         fieldName = in.readString();
-        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"
-                );
-            }
-        }
         missing = in.readGenericValue();
         order = in.readOptionalWriteable(SortOrder::readFromStream);
         sortMode = in.readOptionalWriteable(SortMode::readFromStream);
@@ -153,10 +144,6 @@ public FieldSortBuilder(StreamInput in) throws IOException {
     @Override
     public void writeTo(StreamOutput out) throws IOException {
         out.writeString(fieldName);
-        if (out.getTransportVersion().before(TransportVersions.V_8_0_0)) {
-            out.writeOptionalNamedWriteable(null);
-            out.writeOptionalString(null);
-        }
         out.writeGenericValue(missing);
         out.writeOptionalWriteable(order);
         out.writeOptionalWriteable(sortMode);