diff --git a/build.gradle b/build.gradle
index 4d23e66873b..7e067b89978 100644
--- a/build.gradle
+++ b/build.gradle
@@ -163,8 +163,8 @@ task verifyVersions {
  * the enabled state of every bwc task. It should be set back to true
  * after the backport of the backcompat code is complete.
  */
-final boolean bwc_tests_enabled = false
-final String bwc_tests_disabled_issue = "https://github.com/elastic/elasticsearch/pull/36555" /* place a PR link here when committing bwc changes */
+final boolean bwc_tests_enabled = true
+final String bwc_tests_disabled_issue = "" /* place a PR link here when committing bwc changes */
 if (bwc_tests_enabled == false) {
   if (bwc_tests_disabled_issue.isEmpty()) {
     throw new GradleException("bwc_tests_disabled_issue must be set when bwc_tests_enabled == false")
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 59e6c437809..7d80b769aa5 100644
--- a/server/src/main/java/org/elasticsearch/action/delete/DeleteRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/delete/DeleteRequest.java
@@ -282,7 +282,7 @@ public class DeleteRequest extends ReplicatedWriteRequest<DeleteRequest>
         }
         version = in.readLong();
         versionType = VersionType.fromValue(in.readByte());
-        if (in.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
             ifSeqNo = in.readZLong();
             ifPrimaryTerm = in.readVLong();
         } else {
@@ -302,7 +302,7 @@ public class DeleteRequest extends ReplicatedWriteRequest<DeleteRequest>
         }
         out.writeLong(version);
         out.writeByte(versionType.getValue());
-        if (out.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
             out.writeZLong(ifSeqNo);
             out.writeVLong(ifPrimaryTerm);
         } else if (ifSeqNo != SequenceNumbers.UNASSIGNED_SEQ_NO || ifPrimaryTerm != 0) {
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 e2c097a39b0..46028a7c036 100644
--- a/server/src/main/java/org/elasticsearch/action/index/IndexRequest.java
+++ b/server/src/main/java/org/elasticsearch/action/index/IndexRequest.java
@@ -616,7 +616,7 @@ public class IndexRequest extends ReplicatedWriteRequest<IndexRequest> implement
         } else {
             contentType = null;
         }
-        if (in.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
             ifSeqNo = in.readZLong();
             ifPrimaryTerm = in.readVLong();
         } else {
@@ -654,7 +654,7 @@ public class IndexRequest extends ReplicatedWriteRequest<IndexRequest> implement
         } else {
             out.writeBoolean(false);
         }
-        if (out.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
             out.writeZLong(ifSeqNo);
             out.writeVLong(ifPrimaryTerm);
         } else if (ifSeqNo != SequenceNumbers.UNASSIGNED_SEQ_NO || ifPrimaryTerm != 0) {
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 2b3b1b8f4f2..5ec448888b3 100644
--- a/server/src/main/java/org/elasticsearch/index/get/GetResult.java
+++ b/server/src/main/java/org/elasticsearch/index/get/GetResult.java
@@ -384,7 +384,7 @@ public class GetResult implements Streamable, Iterable<DocumentField>, ToXConten
         index = in.readString();
         type = in.readOptionalString();
         id = in.readString();
-        if (in.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (in.getVersion().onOrAfter(Version.V_6_6_0)) {
             seqNo = in.readZLong();
             primaryTerm = in.readVLong();
         } else {
@@ -416,7 +416,7 @@ public class GetResult implements Streamable, Iterable<DocumentField>, ToXConten
         out.writeString(index);
         out.writeOptionalString(type);
         out.writeString(id);
-        if (out.getVersion().onOrAfter(Version.V_7_0_0)) {
+        if (out.getVersion().onOrAfter(Version.V_6_6_0)) {
             out.writeZLong(seqNo);
             out.writeVLong(primaryTerm);
         }