SERVER-41230 Update FCV constants throughout server code following 4.2 branch

SERVER-42162 Update Execution-related generic upgrade/downgrade references
SERVER-42642 Update Replication-related generic upgrade/downgrade references
SERVER-42592 Update Sharding-related generic upgrade/downgrade references
SERVER-42794 Update Query-related generic upgrade/downgrade references
SERVER-41545 Bump wire protocol version for 4.4

34 files changed, 243 insertions, 309 deletions

diff --git a/src/mongo/db/catalog/coll_mod.cpp b/src/mongo/db/catalog/coll_mod.cpp
index c881c88df99..0d51e406f6e 100644
--- a/src/mongo/db/catalog/coll_mod.cpp
+++ b/src/mongo/db/catalog/coll_mod.cpp
@@ -171,14 +171,14 @@ StatusWith<CollModRequest> parseCollModRequest(OperationContext* opCtx,
             // Save this to a variable to avoid reading the atomic variable multiple times.
             const auto currentFCV = serverGlobalParams.featureCompatibility.getVersion();
 
-            // If the feature compatibility version is not 4.2, and we are validating features as
-            // master, ban the use of new agg features introduced in 4.2 to prevent them from being
+            // If the feature compatibility version is not 4.4, and we are validating features as
+            // master, ban the use of new agg features introduced in 4.4 to prevent them from being
             // persisted in the catalog.
             boost::optional<ServerGlobalParams::FeatureCompatibility::Version>
                 maxFeatureCompatibilityVersion;
             if (serverGlobalParams.validateFeaturesAsMaster.load() &&
                 currentFCV !=
-                    ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
+                    ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
                 maxFeatureCompatibilityVersion = currentFCV;
             }
             auto statusW = coll->parseValidator(opCtx,
diff --git a/src/mongo/db/catalog/database_impl.cpp b/src/mongo/db/catalog/database_impl.cpp
index 467651ae53d..ae069818043 100644
--- a/src/mongo/db/catalog/database_impl.cpp
+++ b/src/mongo/db/catalog/database_impl.cpp
@@ -833,11 +833,11 @@ Status DatabaseImpl::userCreateNS(OperationContext* opCtx,
         // Save this to a variable to avoid reading the atomic variable multiple times.
         const auto currentFCV = serverGlobalParams.featureCompatibility.getVersion();
 
-        // If the feature compatibility version is not 4.2, and we are validating features as
-        // master, ban the use of new agg features introduced in 4.2 to prevent them from being
+        // If the feature compatibility version is not 4.4, and we are validating features as
+        // master, ban the use of new agg features introduced in 4.4 to prevent them from being
         // persisted in the catalog.
         if (serverGlobalParams.validateFeaturesAsMaster.load() &&
-            currentFCV != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
+            currentFCV != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
             expCtx->maxFeatureCompatibilityVersion = currentFCV;
         }
         auto statusWithMatcher =
diff --git a/src/mongo/db/catalog/index_key_validate.cpp b/src/mongo/db/catalog/index_key_validate.cpp
index 83c6812f5b1..4b1f35ce1a6 100644
--- a/src/mongo/db/catalog/index_key_validate.cpp
+++ b/src/mongo/db/catalog/index_key_validate.cpp
@@ -305,15 +305,6 @@ StatusWith<BSONObj> validateIndexSpec(
                                 << "Values in the index key pattern cannot be empty strings"};
                 }
             }
-
-            if ((featureCompatibility.getVersion() <
-                 ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) &&
-                (IndexNames::findPluginName(indexSpec.getObjectField(
-                     IndexDescriptor::kKeyPatternFieldName)) == IndexNames::WILDCARD)) {
-                return {ErrorCodes::CannotCreateIndex,
-                        str::stream()
-                            << "Wildcard indexes require feature compatibility version 4.2"};
-            }
             hasKeyPatternField = true;
         } else if (IndexDescriptor::kIndexNameFieldName == indexSpecElemFieldName) {
             if (indexSpecElem.type() != BSONType::String) {
diff --git a/src/mongo/db/catalog/index_spec_validate_test.cpp b/src/mongo/db/catalog/index_spec_validate_test.cpp
index cb2d66df78f..72343c238f7 100644
--- a/src/mongo/db/catalog/index_spec_validate_test.cpp
+++ b/src/mongo/db/catalog/index_spec_validate_test.cpp
@@ -44,7 +44,6 @@
 #include "mongo/db/query/query_knobs_gen.h"
 #include "mongo/db/query/query_test_service_context.h"
 #include "mongo/db/server_options.h"
-#include "mongo/unittest/ensure_fcv.h"
 #include "mongo/unittest/unittest.h"
 
 namespace mongo {
@@ -53,7 +52,6 @@ namespace {
 using index_key_validate::validateIdIndexSpec;
 using index_key_validate::validateIndexSpec;
 using index_key_validate::validateIndexSpecCollation;
-using unittest::EnsureFCV;
 
 constexpr OperationContext* kDefaultOpCtx = nullptr;
 
@@ -554,7 +552,6 @@ TEST(IndexSpecPartialFilterTest, AcceptsValidPartialFilterExpression) {
 }
 
 TEST(IndexSpecWildcard, SucceedsWithInclusion) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result =
         validateIndexSpec(kDefaultOpCtx,
                           BSON("key" << BSON("$**" << 1) << "name"
@@ -565,7 +562,6 @@ TEST(IndexSpecWildcard, SucceedsWithInclusion) {
 }
 
 TEST(IndexSpecWildcard, SucceedsWithExclusion) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result =
         validateIndexSpec(kDefaultOpCtx,
                           BSON("key" << BSON("$**" << 1) << "name"
@@ -576,7 +572,6 @@ TEST(IndexSpecWildcard, SucceedsWithExclusion) {
 }
 
 TEST(IndexSpecWildcard, SucceedsWithExclusionIncludingId) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -587,7 +582,6 @@ TEST(IndexSpecWildcard, SucceedsWithExclusionIncludingId) {
 }
 
 TEST(IndexSpecWildcard, SucceedsWithInclusionExcludingId) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -598,7 +592,6 @@ TEST(IndexSpecWildcard, SucceedsWithInclusionExcludingId) {
 }
 
 TEST(IndexSpecWildcard, FailsWithInclusionExcludingIdSubfield) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -609,7 +602,6 @@ TEST(IndexSpecWildcard, FailsWithInclusionExcludingIdSubfield) {
 }
 
 TEST(IndexSpecWildcard, FailsWithExclusionIncludingIdSubfield) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -619,19 +611,7 @@ TEST(IndexSpecWildcard, FailsWithExclusionIncludingIdSubfield) {
     ASSERT_EQ(result.getStatus().code(), 40178);
 }
 
-TEST(IndexSpecWildcard, FailsWithImproperFeatureCompatabilityVersion) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
-    serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42);
-    auto result = validateIndexSpec(kDefaultOpCtx,
-                                    BSON("key" << BSON("$**" << 1) << "name"
-                                               << "indexName"),
-                                    serverGlobalParams.featureCompatibility);
-    ASSERT_EQ(result.getStatus().code(), ErrorCodes::CannotCreateIndex);
-}
-
 TEST(IndexSpecWildcard, FailsWithMixedProjection) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result =
         validateIndexSpec(kDefaultOpCtx,
                           BSON("key" << BSON("$**" << 1) << "name"
@@ -642,7 +622,6 @@ TEST(IndexSpecWildcard, FailsWithMixedProjection) {
 }
 
 TEST(IndexSpecWildcard, FailsWithComputedFieldsInProjection) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -654,7 +633,6 @@ TEST(IndexSpecWildcard, FailsWithComputedFieldsInProjection) {
 }
 
 TEST(IndexSpecWildcard, FailsWhenProjectionPluginNotWildcard) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("a" << 1) << "name"
                                                << "indexName"
@@ -664,7 +642,6 @@ TEST(IndexSpecWildcard, FailsWhenProjectionPluginNotWildcard) {
 }
 
 TEST(IndexSpecWildcard, FailsWhenProjectionIsNotAnObject) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -674,7 +651,6 @@ TEST(IndexSpecWildcard, FailsWhenProjectionIsNotAnObject) {
 }
 
 TEST(IndexSpecWildcard, FailsWithEmptyProjection) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("$**" << 1) << "name"
                                                << "indexName"
@@ -684,7 +660,6 @@ TEST(IndexSpecWildcard, FailsWithEmptyProjection) {
 }
 
 TEST(IndexSpecWildcard, FailsWhenInclusionWithSubpath) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("a.$**" << 1) << "name"
                                                << "indexName"
@@ -694,7 +669,6 @@ TEST(IndexSpecWildcard, FailsWhenInclusionWithSubpath) {
 }
 
 TEST(IndexSpecWildcard, FailsWhenExclusionWithSubpath) {
-    EnsureFCV guard(ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
     auto result = validateIndexSpec(kDefaultOpCtx,
                                     BSON("key" << BSON("a.$**" << 1) << "name"
                                                << "indexName"
diff --git a/src/mongo/db/catalog/multi_index_block.cpp b/src/mongo/db/catalog/multi_index_block.cpp
index a1a3ab6d3af..3ebf1ce4935 100644
--- a/src/mongo/db/catalog/multi_index_block.cpp
+++ b/src/mongo/db/catalog/multi_index_block.cpp
@@ -72,19 +72,11 @@ namespace {
  * step down.  A deadlock could result if the index build was attempting to acquire a Collection S
  * or X lock while a prepared transaction held a Collection IX lock, and a step down was waiting to
  * acquire the RSTL in mode X.
- * We should only drop the RSTL while in FCV 4.2, as prepared transactions can only
- * occur in FCV 4.2.
  */
 void _unlockRSTLForIndexCleanup(OperationContext* opCtx) {
     if (!serverGlobalParams.featureCompatibility.isVersionInitialized()) {
         return;
     }
-
-    if (serverGlobalParams.featureCompatibility.getVersion() !=
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
-        return;
-    }
-
     opCtx->lockState()->unlockRSTLforPrepare();
     invariant(!opCtx->lockState()->isRSTLLocked());
 }
diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index ec1d65deb3b..0a7482078b4 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -69,9 +69,9 @@ void FeatureCompatibilityVersion::setTargetUpgrade(OperationContext* opCtx) {
     // Sets both 'version' and 'targetVersion' fields.
     _runUpdateCommand(opCtx, [](auto updateMods) {
         updateMods.append(FeatureCompatibilityVersionParser::kVersionField,
-                          FeatureCompatibilityVersionParser::kVersion40);
-        updateMods.append(FeatureCompatibilityVersionParser::kTargetVersionField,
                           FeatureCompatibilityVersionParser::kVersion42);
+        updateMods.append(FeatureCompatibilityVersionParser::kTargetVersionField,
+                          FeatureCompatibilityVersionParser::kVersion44);
     });
 }
 
@@ -79,9 +79,9 @@ void FeatureCompatibilityVersion::setTargetDowngrade(OperationContext* opCtx) {
     // Sets both 'version' and 'targetVersion' fields.
     _runUpdateCommand(opCtx, [](auto updateMods) {
         updateMods.append(FeatureCompatibilityVersionParser::kVersionField,
-                          FeatureCompatibilityVersionParser::kVersion40);
+                          FeatureCompatibilityVersionParser::kVersion42);
         updateMods.append(FeatureCompatibilityVersionParser::kTargetVersionField,
-                          FeatureCompatibilityVersionParser::kVersion40);
+                          FeatureCompatibilityVersionParser::kVersion42);
     });
 }
 
@@ -124,8 +124,8 @@ void FeatureCompatibilityVersion::setIfCleanStartup(OperationContext* opCtx,
         repl::TimestampedBSONObj{
             BSON("_id" << FeatureCompatibilityVersionParser::kParameterName
                        << FeatureCompatibilityVersionParser::kVersionField
-                       << (storeUpgradeVersion ? FeatureCompatibilityVersionParser::kVersion42
-                                               : FeatureCompatibilityVersionParser::kVersion40)),
+                       << (storeUpgradeVersion ? FeatureCompatibilityVersionParser::kVersion44
+                                               : FeatureCompatibilityVersionParser::kVersion42)),
             Timestamp()},
         repl::OpTime::kUninitializedTerm));  // No timestamp or term because this write is not
                                              // replicated.
@@ -165,7 +165,7 @@ void FeatureCompatibilityVersion::onInsertOrUpdate(OperationContext* opCtx, cons
         serverGlobalParams.featureCompatibility.setVersion(newVersion);
         updateMinWireVersion();
 
-        if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40) {
+        if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42) {
             // Close all incoming connections from internal clients with binary versions lower than
             // ours.
             opCtx->getServiceContext()->getServiceEntryPoint()->endAllSessions(
@@ -176,7 +176,7 @@ void FeatureCompatibilityVersion::onInsertOrUpdate(OperationContext* opCtx, cons
                 .dropConnections(transport::Session::kKeepOpen);
         }
 
-        if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
+        if (newVersion != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
             if (MONGO_FAIL_POINT(hangBeforeAbortingRunningTransactionsOnFCVDowngrade)) {
                 log() << "featureCompatibilityVersion - "
                          "hangBeforeAbortingRunningTransactionsOnFCVDowngrade fail point enabled. "
@@ -196,17 +196,17 @@ void FeatureCompatibilityVersion::updateMinWireVersion() {
     WireSpec& spec = WireSpec::instance();
 
     switch (serverGlobalParams.featureCompatibility.getVersion()) {
-        case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42:
-        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42:
-        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo40:
+        case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44:
+        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44:
+        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo42:
             spec.incomingInternalClient.minWireVersion = LATEST_WIRE_VERSION;
             spec.outgoing.minWireVersion = LATEST_WIRE_VERSION;
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40:
+        case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42:
             spec.incomingInternalClient.minWireVersion = LATEST_WIRE_VERSION - 1;
             spec.outgoing.minWireVersion = LATEST_WIRE_VERSION - 1;
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault40Behavior:
+        case ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault42Behavior:
             // getVersion() does not return this value.
             MONGO_UNREACHABLE;
     }
@@ -215,11 +215,11 @@ void FeatureCompatibilityVersion::updateMinWireVersion() {
 void FeatureCompatibilityVersion::_validateVersion(StringData version) {
     uassert(40284,
             str::stream() << "featureCompatibilityVersion must be '"
-                          << FeatureCompatibilityVersionParser::kVersion42 << "' or '"
-                          << FeatureCompatibilityVersionParser::kVersion40 << "'. See "
+                          << FeatureCompatibilityVersionParser::kVersion44 << "' or '"
+                          << FeatureCompatibilityVersionParser::kVersion42 << "'. See "
                           << feature_compatibility_version_documentation::kCompatibilityLink << ".",
-            version == FeatureCompatibilityVersionParser::kVersion42 ||
-                version == FeatureCompatibilityVersionParser::kVersion40);
+            version == FeatureCompatibilityVersionParser::kVersion44 ||
+                version == FeatureCompatibilityVersionParser::kVersion42);
 }
 
 void FeatureCompatibilityVersion::_runUpdateCommand(OperationContext* opCtx,
@@ -275,33 +275,33 @@ void FeatureCompatibilityVersionParameter::append(OperationContext* opCtx,
 
     BSONObjBuilder featureCompatibilityVersionBuilder(b.subobjStart(name));
     switch (serverGlobalParams.featureCompatibility.getVersion()) {
-        case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42:
+        case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
-                FeatureCompatibilityVersionParser::kVersion42);
+                FeatureCompatibilityVersionParser::kVersion44);
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42:
+        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
-                FeatureCompatibilityVersionParser::kVersion40);
+                FeatureCompatibilityVersionParser::kVersion42);
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kTargetVersionField,
-                FeatureCompatibilityVersionParser::kVersion42);
+                FeatureCompatibilityVersionParser::kVersion44);
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo40:
+        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo42:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
-                FeatureCompatibilityVersionParser::kVersion40);
+                FeatureCompatibilityVersionParser::kVersion42);
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kTargetVersionField,
-                FeatureCompatibilityVersionParser::kVersion40);
+                FeatureCompatibilityVersionParser::kVersion42);
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40:
+        case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
-                FeatureCompatibilityVersionParser::kVersion40);
+                FeatureCompatibilityVersionParser::kVersion42);
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault40Behavior:
+        case ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault42Behavior:
             // getVersion() does not return this value.
             MONGO_UNREACHABLE;
     }
diff --git a/src/mongo/db/commands/feature_compatibility_version.h b/src/mongo/db/commands/feature_compatibility_version.h
index c6f7a7f97d8..1c650fa1f0d 100644
--- a/src/mongo/db/commands/feature_compatibility_version.h
+++ b/src/mongo/db/commands/feature_compatibility_version.h
@@ -52,24 +52,23 @@ public:
     static Lock::ResourceMutex fcvLock;
 
     /**
-     * Records intent to perform a 4.0 -> 4.2 upgrade by updating the on-disk feature
-     * compatibility version document to have 'version'=4.0, 'targetVersion'=4.2.
+     * Records intent to perform a 4.2 -> 4.4 upgrade by updating the on-disk feature
+     * compatibility version document to have 'version'=4.2, 'targetVersion'=4.4.
      * Should be called before schemas are modified.
      */
     static void setTargetUpgrade(OperationContext* opCtx);
 
     /**
-     * Records intent to perform a 4.2 -> 4.0 downgrade by updating the on-disk feature
-     * compatibility version document to have 'version'=4.0, 'targetVersion'=4.0.
+     * Records intent to perform a 4.4 -> 4.2 downgrade by updating the on-disk feature
+     * compatibility version document to have 'version'=4.2, 'targetVersion'=4.2.
      * Should be called before schemas are modified.
      */
     static void setTargetDowngrade(OperationContext* opCtx);
 
     /**
-     * Records the completion of a 4.0 <-> 4.2 upgrade or downgrade by updating the on-disk feature
+     * Records the completion of a 4.2 <-> 4.4 upgrade or downgrade by updating the on-disk feature
      * compatibility version document to have 'version'=version and unsetting the 'targetVersion'
-     * field.
-     * Should be called after schemas are modified.
+     * field. Should be called after schemas are modified.
      */
     static void unsetTargetUpgradeOrDowngrade(OperationContext* opCtx, StringData version);
 
diff --git a/src/mongo/db/commands/feature_compatibility_version_command_parser.cpp b/src/mongo/db/commands/feature_compatibility_version_command_parser.cpp
index 919a2aae34c..1450e35ece6 100644
--- a/src/mongo/db/commands/feature_compatibility_version_command_parser.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version_command_parser.cpp
@@ -77,12 +77,12 @@ StatusWith<std::string> FeatureCompatibilityVersionCommandParser::extractVersion
 
     const std::string version = versionElem.String();
 
-    if (version != FeatureCompatibilityVersionParser::kVersion42 &&
-        version != FeatureCompatibilityVersionParser::kVersion40) {
+    if (version != FeatureCompatibilityVersionParser::kVersion44 &&
+        version != FeatureCompatibilityVersionParser::kVersion42) {
         return {ErrorCodes::BadValue,
                 str::stream() << "Invalid command argument. Expected '"
-                              << FeatureCompatibilityVersionParser::kVersion42 << "' or '"
-                              << FeatureCompatibilityVersionParser::kVersion40 << "', found "
+                              << FeatureCompatibilityVersionParser::kVersion44 << "' or '"
+                              << FeatureCompatibilityVersionParser::kVersion42 << "', found "
                               << version << " in: " << cmdObj << ". See "
                               << feature_compatibility_version_documentation::kCompatibilityLink
                               << "."};
diff --git a/src/mongo/db/commands/feature_compatibility_version_parser.cpp b/src/mongo/db/commands/feature_compatibility_version_parser.cpp
index 0aa872b9041..d542d23c7a3 100644
--- a/src/mongo/db/commands/feature_compatibility_version_parser.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version_parser.cpp
@@ -38,10 +38,10 @@
 
 namespace mongo {
 
-constexpr StringData FeatureCompatibilityVersionParser::kVersion40;
 constexpr StringData FeatureCompatibilityVersionParser::kVersion42;
-constexpr StringData FeatureCompatibilityVersionParser::kVersionDowngradingTo40;
-constexpr StringData FeatureCompatibilityVersionParser::kVersionUpgradingTo42;
+constexpr StringData FeatureCompatibilityVersionParser::kVersion44;
+constexpr StringData FeatureCompatibilityVersionParser::kVersionDowngradingTo42;
+constexpr StringData FeatureCompatibilityVersionParser::kVersionUpgradingTo44;
 constexpr StringData FeatureCompatibilityVersionParser::kVersionUnset;
 
 constexpr StringData FeatureCompatibilityVersionParser::kParameterName;
@@ -51,7 +51,7 @@ constexpr StringData FeatureCompatibilityVersionParser::kTargetVersionField;
 StatusWith<ServerGlobalParams::FeatureCompatibility::Version>
 FeatureCompatibilityVersionParser::parse(const BSONObj& featureCompatibilityVersionDoc) {
     ServerGlobalParams::FeatureCompatibility::Version version =
-        ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault40Behavior;
+        ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault42Behavior;
     std::string versionString;
     std::string targetVersionString;
 
@@ -72,12 +72,12 @@ FeatureCompatibilityVersionParser::parse(const BSONObj& featureCompatibilityVers
                                   << ".");
             }
 
-            if (elem.String() != kVersion42 && elem.String() != kVersion40) {
+            if (elem.String() != kVersion44 && elem.String() != kVersion42) {
                 return Status(ErrorCodes::BadValue,
                               str::stream()
                                   << "Invalid value for " << fieldName << ", found "
-                                  << elem.String() << ", expected '" << kVersion42 << "' or '"
-                                  << kVersion40 << "'. Contents of " << kParameterName
+                                  << elem.String() << ", expected '" << kVersion44 << "' or '"
+                                  << kVersion42 << "'. Contents of " << kParameterName
                                   << " document in "
                                   << NamespaceString::kServerConfigurationNamespace.toString()
                                   << ": " << featureCompatibilityVersionDoc << ". See "
@@ -102,16 +102,16 @@ FeatureCompatibilityVersionParser::parse(const BSONObj& featureCompatibilityVers
         }
     }
 
-    if (versionString == kVersion40) {
-        if (targetVersionString == kVersion42) {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42;
-        } else if (targetVersionString == kVersion40) {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo40;
+    if (versionString == kVersion42) {
+        if (targetVersionString == kVersion44) {
+            version = ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44;
+        } else if (targetVersionString == kVersion42) {
+            version = ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo42;
         } else {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40;
+            version = ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42;
         }
-    } else if (versionString == kVersion42) {
-        if (targetVersionString == kVersion42 || targetVersionString == kVersion40) {
+    } else if (versionString == kVersion44) {
+        if (targetVersionString == kVersion44 || targetVersionString == kVersion42) {
             return Status(ErrorCodes::BadValue,
                           str::stream()
                               << "Invalid state for " << kParameterName << " document in "
@@ -120,7 +120,7 @@ FeatureCompatibilityVersionParser::parse(const BSONObj& featureCompatibilityVers
                               << feature_compatibility_version_documentation::kCompatibilityLink
                               << ".");
         } else {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42;
+            version = ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44;
         }
     } else {
         return Status(ErrorCodes::BadValue,
diff --git a/src/mongo/db/commands/feature_compatibility_version_parser.h b/src/mongo/db/commands/feature_compatibility_version_parser.h
index f563e09af2c..757d725a0bf 100644
--- a/src/mongo/db/commands/feature_compatibility_version_parser.h
+++ b/src/mongo/db/commands/feature_compatibility_version_parser.h
@@ -40,10 +40,10 @@ namespace mongo {
  */
 class FeatureCompatibilityVersionParser {
 public:
-    static constexpr StringData kVersion40 = "4.0"_sd;
     static constexpr StringData kVersion42 = "4.2"_sd;
-    static constexpr StringData kVersionDowngradingTo40 = "downgrading to 4.0"_sd;
-    static constexpr StringData kVersionUpgradingTo42 = "upgrading to 4.2"_sd;
+    static constexpr StringData kVersion44 = "4.4"_sd;
+    static constexpr StringData kVersionDowngradingTo42 = "downgrading to 4.2"_sd;
+    static constexpr StringData kVersionUpgradingTo44 = "upgrading to 4.4"_sd;
     static constexpr StringData kVersionUnset = "Unset"_sd;
 
     static constexpr StringData kParameterName = "featureCompatibilityVersion"_sd;
@@ -63,16 +63,16 @@ public:
      */
     static StringData toString(ServerGlobalParams::FeatureCompatibility::Version version) {
         switch (version) {
-            case ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault40Behavior:
+            case ServerGlobalParams::FeatureCompatibility::Version::kUnsetDefault42Behavior:
                 return kVersionUnset;
-            case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40:
-                return kVersion40;
-            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42:
-                return kVersionUpgradingTo42;
-            case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo40:
-                return kVersionDowngradingTo40;
-            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42:
+            case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42:
                 return kVersion42;
+            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44:
+                return kVersionUpgradingTo44;
+            case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo42:
+                return kVersionDowngradingTo42;
+            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44:
+                return kVersion44;
             default:
                 MONGO_UNREACHABLE;
         }
diff --git a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
index 0238f1bf004..cfe59311ab4 100644
--- a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
+++ b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
@@ -62,7 +62,7 @@ MONGO_FAIL_POINT_DEFINE(featureCompatibilityDowngrade);
 MONGO_FAIL_POINT_DEFINE(featureCompatibilityUpgrade);
 
 /**
- * Sets the minimum allowed version for the cluster. If it is 4.0, then the node should not use 4.2
+ * Sets the minimum allowed version for the cluster. If it is 4.2, then the node should not use 4.4
  * features.
  *
  * Format:
@@ -88,13 +88,13 @@ public:
     }
 
     std::string help() const override {
+        using FCVP = FeatureCompatibilityVersionParser;
         std::stringstream h;
-        h << "Set the API version exposed by this node. If set to \""
-          << FeatureCompatibilityVersionParser::kVersion40
-          << "\", then 4.2 features are disabled. If \""
-          << FeatureCompatibilityVersionParser::kVersion42
-          << "\", then 4.2 features are enabled, and all nodes in the cluster must be binary "
-             "version 4.2. See "
+        h << "Set the API version exposed by this node. If set to '" << FCVP::kVersion42
+          << "', then " << FCVP::kVersion44 << " features are disabled. If set to '"
+          << FCVP::kVersion44 << "', then " << FCVP::kVersion44
+          << " features are enabled, and all nodes in the cluster must be binary version "
+          << FCVP::kVersion44 << ". See "
           << feature_compatibility_version_documentation::kCompatibilityLink << ".";
         return h.str();
     }
@@ -143,16 +143,16 @@ public:
         ServerGlobalParams::FeatureCompatibility::Version actualVersion =
             serverGlobalParams.featureCompatibility.getVersion();
 
-        if (requestedVersion == FeatureCompatibilityVersionParser::kVersion42) {
+        if (requestedVersion == FeatureCompatibilityVersionParser::kVersion44) {
             uassert(ErrorCodes::IllegalOperation,
-                    "cannot initiate featureCompatibilityVersion upgrade to 4.2 while a previous "
-                    "featureCompatibilityVersion downgrade to 4.0 has not completed. Finish "
-                    "downgrade to 4.0, then upgrade to 4.2.",
+                    "cannot initiate featureCompatibilityVersion upgrade to 4.4 while a previous "
+                    "featureCompatibilityVersion downgrade to 4.2 has not completed. Finish "
+                    "downgrade to 4.2, then upgrade to 4.4.",
                     actualVersion !=
-                        ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo40);
+                        ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo42);
 
             if (actualVersion ==
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
+                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
                 // Set the client's last opTime to the system last opTime so no-ops wait for
                 // writeConcern.
                 repl::ReplClientInfo::forClient(opCtx->getClient())
@@ -166,7 +166,7 @@ public:
                 // Take the global lock in S mode to create a barrier for operations taking the
                 // global IX or X locks. This ensures that either
                 //   - The global IX/X locked operation will start after the FCV change, see the
-                //     upgrading to 4.2 FCV and act accordingly.
+                //     upgrading to 4.4 FCV and act accordingly.
                 //   - The global IX/X locked operation began prior to the FCV change, is acting on
                 //     that assumption and will finish before upgrade procedures begin right after
                 //     this.
@@ -186,15 +186,15 @@ public:
             }
 
             FeatureCompatibilityVersion::unsetTargetUpgradeOrDowngrade(opCtx, requestedVersion);
-        } else if (requestedVersion == FeatureCompatibilityVersionParser::kVersion40) {
+        } else if (requestedVersion == FeatureCompatibilityVersionParser::kVersion42) {
             uassert(ErrorCodes::IllegalOperation,
-                    "cannot initiate setting featureCompatibilityVersion to 4.0 while a previous "
-                    "featureCompatibilityVersion upgrade to 4.2 has not completed.",
+                    "cannot initiate setting featureCompatibilityVersion to 4.2 while a previous "
+                    "featureCompatibilityVersion upgrade to 4.4 has not completed.",
                     actualVersion !=
-                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42);
+                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44);
 
             if (actualVersion ==
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40) {
+                ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42) {
                 // Set the client's last opTime to the system last opTime so no-ops wait for
                 // writeConcern.
                 repl::ReplClientInfo::forClient(opCtx->getClient())
@@ -208,7 +208,7 @@ public:
                 // Take the global lock in S mode to create a barrier for operations taking the
                 // global IX or X locks. This ensures that either
                 //   - The global IX/X locked operation will start after the FCV change, see the
-                //     downgrading to 4.0 FCV and act accordingly.
+                //     downgrading to 4.2 FCV and act accordingly.
                 //   - The global IX/X locked operation began prior to the FCV change, is acting on
                 //     that assumption and will finish before downgrade procedures begin right after
                 //     this.
diff --git a/src/mongo/db/index_builds_coordinator.cpp b/src/mongo/db/index_builds_coordinator.cpp
index dfe963eb877..50db2b33c2b 100644
--- a/src/mongo/db/index_builds_coordinator.cpp
+++ b/src/mongo/db/index_builds_coordinator.cpp
@@ -780,13 +780,8 @@ void IndexBuildsCoordinator::_runIndexBuildInner(OperationContext* opCtx,
             // deadlock could result if the index build was attempting to acquire a Collection S or
             // X lock while a prepared transaction held a Collection IX lock, and a step down was
             // waiting to acquire the RSTL in mode X.
-            // We should only drop the RSTL while in FCV 4.2, as prepared transactions can only
-            // occur in FCV 4.2.
-            if (serverGlobalParams.featureCompatibility.getVersion() ==
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
-                const bool unlocked = opCtx->lockState()->unlockRSTLforPrepare();
-                invariant(unlocked);
-            }
+            const bool unlocked = opCtx->lockState()->unlockRSTLforPrepare();
+            invariant(unlocked);
             opCtx->runWithoutInterruptionExceptAtGlobalShutdown(
                 [&, this] { _buildIndex(opCtx, collection, *nss, replState, &collLock); });
         } else {
diff --git a/src/mongo/db/repair_database_and_check_version.cpp b/src/mongo/db/repair_database_and_check_version.cpp
index 01c965cb9d3..4f4d7d47fc3 100644
--- a/src/mongo/db/repair_database_and_check_version.cpp
+++ b/src/mongo/db/repair_database_and_check_version.cpp
@@ -74,8 +74,8 @@ MONGO_FAIL_POINT_DEFINE(exitBeforeRepairInvalidatesConfig);
 namespace {
 
 const std::string mustDowngradeErrorMsg = str::stream()
-    << "UPGRADE PROBLEM: The data files need to be fully upgraded to version 4.0 before attempting "
-       "an upgrade to 4.2; see "
+    << "UPGRADE PROBLEM: The data files need to be fully upgraded to version 4.2 before attempting "
+       "an upgrade to 4.4; see "
     << feature_compatibility_version_documentation::kUpgradeLink << " for more details.";
 
 Status restoreMissingFeatureCompatibilityVersionDocument(OperationContext* opCtx,
@@ -111,11 +111,11 @@ Status restoreMissingFeatureCompatibilityVersionDocument(OperationContext* opCtx
                           BSON("_id" << FeatureCompatibilityVersionParser::kParameterName),
                           featureCompatibilityVersion)) {
         log() << "Re-creating featureCompatibilityVersion document that was deleted with version "
-              << FeatureCompatibilityVersionParser::kVersion40 << ".";
+              << FeatureCompatibilityVersionParser::kVersion42 << ".";
 
         BSONObj fcvObj = BSON("_id" << FeatureCompatibilityVersionParser::kParameterName
                                     << FeatureCompatibilityVersionParser::kVersionField
-                                    << FeatureCompatibilityVersionParser::kVersion40);
+                                    << FeatureCompatibilityVersionParser::kVersion42);
 
         writeConflictRetry(opCtx, "insertFCVDocument", fcvNss.ns(), [&] {
             WriteUnitOfWork wunit(opCtx);
@@ -504,7 +504,7 @@ bool repairDatabasesAndCheckVersion(OperationContext* opCtx) {
                     auto swVersion =
                         FeatureCompatibilityVersionParser::parse(featureCompatibilityVersion);
                     // Note this error path captures all cases of an FCV document existing,
-                    // but with any value other than "4.0" or "4.2". This includes unexpected
+                    // but with any value other than "4.2" or "4.4". This includes unexpected
                     // cases with no path forward such as the FCV value not being a string.
                     uassert(ErrorCodes::MustDowngrade,
                             str::stream()
@@ -512,7 +512,7 @@ bool repairDatabasesAndCheckVersion(OperationContext* opCtx) {
                                    "featureCompatibilityVersion document (ERROR: "
                                 << swVersion.getStatus()
                                 << "). If the current featureCompatibilityVersion is below "
-                                   "4.0, see the documentation on upgrading at "
+                                   "4.2, see the documentation on upgrading at "
                                 << feature_compatibility_version_documentation::kUpgradeLink << ".",
                             swVersion.isOK());
 
@@ -524,24 +524,24 @@ bool repairDatabasesAndCheckVersion(OperationContext* opCtx) {
                     // On startup, if the version is in an upgrading or downrading state, print a
                     // warning.
                     if (version ==
-                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42) {
+                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44) {
                         log() << "** WARNING: A featureCompatibilityVersion upgrade did not "
                               << "complete. " << startupWarningsLog;
                         log() << "**          The current featureCompatibilityVersion is "
                               << FeatureCompatibilityVersionParser::toString(version) << "."
                               << startupWarningsLog;
                         log() << "**          To fix this, use the setFeatureCompatibilityVersion "
-                              << "command to resume upgrade to 4.2." << startupWarningsLog;
+                              << "command to resume upgrade to 4.4." << startupWarningsLog;
                     } else if (version ==
                                ServerGlobalParams::FeatureCompatibility::Version::
-                                   kDowngradingTo40) {
+                                   kDowngradingTo42) {
                         log() << "** WARNING: A featureCompatibilityVersion downgrade did not "
                               << "complete. " << startupWarningsLog;
                         log() << "**          The current featureCompatibilityVersion is "
                               << FeatureCompatibilityVersionParser::toString(version) << "."
                               << startupWarningsLog;
                         log() << "**          To fix this, use the setFeatureCompatibilityVersion "
-                              << "command to resume downgrade to 4.0." << startupWarningsLog;
+                              << "command to resume downgrade to 4.2." << startupWarningsLog;
                     }
                 }
             }
diff --git a/src/mongo/db/repl/initial_syncer.cpp b/src/mongo/db/repl/initial_syncer.cpp
index a0c250ff58c..8dc2170b6c4 100644
--- a/src/mongo/db/repl/initial_syncer.cpp
+++ b/src/mongo/db/repl/initial_syncer.cpp
@@ -852,8 +852,8 @@ void InitialSyncer::_fcvFetcherCallback(const StatusWith<Fetcher::QueryResponse>
     auto version = fCVParseSW.getValue();
 
     // Changing the featureCompatibilityVersion during initial sync is unsafe.
-    if (version > ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40 &&
-        version < ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
+    if (version > ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42 &&
+        version < ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
         onCompletionGuard->setResultAndCancelRemainingWork_inlock(
             lock,
             Status(ErrorCodes::IncompatibleServerVersion,
diff --git a/src/mongo/db/repl/initial_syncer_test.cpp b/src/mongo/db/repl/initial_syncer_test.cpp
index 47d4283b03b..b9eb16070bc 100644
--- a/src/mongo/db/repl/initial_syncer_test.cpp
+++ b/src/mongo/db/repl/initial_syncer_test.cpp
@@ -206,10 +206,10 @@ public:
 
     /**
      * Schedules and processes a successful response to the network request sent by InitialSyncer's
-     * feature compatibility version fetcher. Always includes a valid fCV=4.0 document in the
-     * response.
+     * feature compatibility version fetcher. Always includes a valid fCV=last-stable document in
+     * the response.
      */
-    void processSuccessfulFCVFetcherResponse40();
+    void processSuccessfulFCVFetcherResponseLastStable();
 
     void finishProcessingNetworkResponse() {
         getNet()->runReadyNetworkOperations();
@@ -591,9 +591,9 @@ void assertFCVRequest(RemoteCommandRequest request) {
                       request.cmdObj.getObjectField("filter"));
 }
 
-void InitialSyncerTest::processSuccessfulFCVFetcherResponse40() {
+void InitialSyncerTest::processSuccessfulFCVFetcherResponseLastStable() {
     auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "version"
-                            << FeatureCompatibilityVersionParser::kVersion40)};
+                            << FeatureCompatibilityVersionParser::kVersion42)};
     processSuccessfulFCVFetcherResponse(docs);
 }
 
@@ -1459,7 +1459,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
     }
 
     initialSyncer->join();
@@ -1608,7 +1608,7 @@ TEST_F(InitialSyncerTest, InitialSyncerResendsFindCommandIfFCVFetcherReturnsRetr
     ASSERT_TRUE(initialSyncer->isActive());
 
     // FCV second attempt.
-    processSuccessfulFCVFetcherResponse40();
+    processSuccessfulFCVFetcherResponseLastStable();
 }
 
 void InitialSyncerTest::runInitialSyncWithBadFCVResponse(std::vector<BSONObj> docs,
@@ -1651,7 +1651,7 @@ TEST_F(InitialSyncerTest,
 TEST_F(InitialSyncerTest,
        InitialSyncerReturnsTooManyMatchingDocumentsWhenFCVFetcherReturnsMultipleDocuments) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "version"
-                            << FeatureCompatibilityVersionParser::kVersion40),
+                            << FeatureCompatibilityVersionParser::kVersion42),
                  BSON("_id"
                       << "other")};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::TooManyMatchingDocuments);
@@ -1660,22 +1660,22 @@ TEST_F(InitialSyncerTest,
 TEST_F(InitialSyncerTest,
        InitialSyncerReturnsIncompatibleServerVersionWhenFCVFetcherReturnsUpgradeTargetVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "version"
-                            << FeatureCompatibilityVersionParser::kVersion40 << "targetVersion"
-                            << FeatureCompatibilityVersionParser::kVersion42)};
+                            << FeatureCompatibilityVersionParser::kVersion42 << "targetVersion"
+                            << FeatureCompatibilityVersionParser::kVersion44)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::IncompatibleServerVersion);
 }
 
 TEST_F(InitialSyncerTest,
        InitialSyncerReturnsIncompatibleServerVersionWhenFCVFetcherReturnsDowngradeTargetVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "version"
-                            << FeatureCompatibilityVersionParser::kVersion40 << "targetVersion"
-                            << FeatureCompatibilityVersionParser::kVersion40)};
+                            << FeatureCompatibilityVersionParser::kVersion42 << "targetVersion"
+                            << FeatureCompatibilityVersionParser::kVersion42)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::IncompatibleServerVersion);
 }
 
 TEST_F(InitialSyncerTest, InitialSyncerReturnsBadValueWhenFCVFetcherReturnsNoVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "targetVersion"
-                            << FeatureCompatibilityVersionParser::kVersion40)};
+                            << FeatureCompatibilityVersionParser::kVersion42)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::BadValue);
 }
 
@@ -1704,7 +1704,7 @@ TEST_F(InitialSyncerTest, InitialSyncerSucceedsWhenFCVFetcherReturnsOldVersion)
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "version"
-                                << FeatureCompatibilityVersionParser::kVersion40)};
+                                << FeatureCompatibilityVersionParser::kVersion42)};
         processSuccessfulFCVFetcherResponse(docs);
         ASSERT_TRUE(net->hasReadyRequests());
     }
@@ -1757,7 +1757,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughOplogFetcherScheduleError) {
         net->runReadyNetworkOperations();
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // OplogFetcher will shut down DatabasesCloner on error after setting the completion status.
         // We call runReadyNetworkOperations() again to deliver the cancellation status to
@@ -1801,7 +1801,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughOplogFetcherCallbackError) {
         net->runReadyNetworkOperations();
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         assertRemoteCommandNameEquals(
             "listDatabases", net->scheduleSuccessfulResponse(makeListDatabasesResponse({})));
@@ -1860,7 +1860,7 @@ TEST_F(InitialSyncerTest,
         net->runReadyNetworkOperations();
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         assertRemoteCommandNameEquals(
             "listDatabases", net->scheduleSuccessfulResponse(makeListDatabasesResponse({})));
@@ -1923,7 +1923,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         assertRemoteCommandNameEquals(
             "listDatabases", net->scheduleSuccessfulResponse(makeListDatabasesResponse({})));
@@ -1984,7 +1984,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         assertRemoteCommandNameEquals(
             "listDatabases", net->scheduleSuccessfulResponse(makeListDatabasesResponse({})));
@@ -2050,7 +2050,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // InitialSyncer shuts down OplogFetcher when it fails to schedule DatabasesCloner
         // so we should not expect any network requests in the queue.
@@ -2096,7 +2096,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // DatabasesCloner's first remote command - listDatabases
         assertRemoteCommandNameEquals(
@@ -2139,7 +2139,7 @@ TEST_F(InitialSyncerTest, InitialSyncerIgnoresLocalDatabasesWhenCloningDatabases
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // DatabasesCloner's first remote command - listDatabases
         assertRemoteCommandNameEquals(
@@ -2208,7 +2208,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // DatabasesCloner's first remote command - listDatabases
         assertRemoteCommandNameEquals(
@@ -2282,7 +2282,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsBothOplogFetcherAndDatabasesCloner
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
     }
 
     ASSERT_OK(initialSyncer->shutdown());
@@ -2338,7 +2338,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2383,7 +2383,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2444,7 +2444,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2500,7 +2500,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2567,7 +2567,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2625,7 +2625,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(2)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2697,7 +2697,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2772,7 +2772,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2847,7 +2847,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2904,7 +2904,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -2966,7 +2966,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsLastRollbackCheckerOnShutdown) {
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3029,7 +3029,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsLastRollbackCheckerOnOplogFetcherC
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3097,7 +3097,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3161,7 +3161,7 @@ TEST_F(InitialSyncerTest, LastOpTimeShouldBeSetEvenIfNoOperationsAreAppliedAfter
         processSuccessfulLastOplogEntryFetcherResponse({oplogEntry.toBSON()});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Instead of fast forwarding to DatabasesCloner completion by returning an empty list of
         // database names, we'll simulate copying a single database with a single collection on the
@@ -3254,7 +3254,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchScheduleE
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3317,7 +3317,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughSecondGetNextApplierBatchSch
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3380,7 +3380,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsGetNextApplierBatchOnShutdown) {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3445,7 +3445,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughGetNextApplierBatchInLockErr
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3518,7 +3518,7 @@ TEST_F(
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3582,7 +3582,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughMultiApplierScheduleError) {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3662,7 +3662,7 @@ TEST_F(InitialSyncerTest, InitialSyncerPassesThroughMultiApplierCallbackError) {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3717,7 +3717,7 @@ TEST_F(InitialSyncerTest, InitialSyncerCancelsGetNextApplierBatchCallbackOnOplog
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3778,7 +3778,7 @@ OplogEntry InitialSyncerTest::doInitialSyncWithOneBatch() {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Quickest path to a successful DatabasesCloner completion is to respond to the
         // listDatabases with an empty list of database names.
@@ -3875,7 +3875,7 @@ TEST_F(InitialSyncerTest,
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Instead of fast forwarding to DatabasesCloner completion by returning an empty list of
         // database names, we'll simulate copying a single database with a single collection on the
@@ -3991,7 +3991,7 @@ TEST_F(InitialSyncerTest, OplogOutOfOrderOnOplogFetchFinish) {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // Ignore listDatabases request.
         auto noi = net->getNextReadyRequest();
@@ -4064,7 +4064,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
     }
 
     log() << "Done playing first failed response";
@@ -4119,7 +4119,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressReturnsCorrectProgress) {
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
     }
 
     log() << "Done playing first successful response";
@@ -4334,7 +4334,7 @@ TEST_F(InitialSyncerTest, GetInitialSyncProgressOmitsClonerStatsIfClonerStatsExc
         processSuccessfulLastOplogEntryFetcherResponse({makeOplogEntryObj(1)});
 
         // Feature Compatibility Version.
-        processSuccessfulFCVFetcherResponse40();
+        processSuccessfulFCVFetcherResponseLastStable();
 
         // listDatabases
         NamespaceString nss("a.a");
diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index 183f2527e19..fd60a8de505 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -2960,7 +2960,7 @@ ReplicationCoordinatorImpl::_updateMemberStateFromTopologyCoordinator(WithLock l
     // receive the replicated version. This is to avoid bugs like SERVER-32639.
     if (newState.arbiter()) {
         serverGlobalParams.featureCompatibility.setVersion(
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
     }
 
     _memberState = newState;
diff --git a/src/mongo/db/repl/replication_recovery.cpp b/src/mongo/db/repl/replication_recovery.cpp
index f13cbeaa21c..dac500778f2 100644
--- a/src/mongo/db/repl/replication_recovery.cpp
+++ b/src/mongo/db/repl/replication_recovery.cpp
@@ -324,10 +324,10 @@ void ReplicationRecoveryImpl::_recoverFromUnstableCheckpoint(OperationContext* o
     //
     // Not waiting for checkpoint durability here can result in a scenario where the node takes
     // writes and persists them to the oplog, but crashes before a stable checkpoint persists a
-    // "recovery timestamp". The typical startup path for data-bearing nodes with 4.0 is to use
-    // the recovery timestamp to determine where to play oplog forward from. As this method shows,
-    // when a recovery timestamp does not exist, the applied through is used to determine where to
-    // start playing oplog entries from.
+    // "recovery timestamp". The typical startup path for data-bearing nodes is to use the recovery
+    // timestamp to determine where to play oplog forward from. As this method shows, when a
+    // recovery timestamp does not exist, the applied through is used to determine where to start
+    // playing oplog entries from.
     opCtx->recoveryUnit()->waitUntilUnjournaledWritesDurable();
 }
 
diff --git a/src/mongo/db/repl/replication_recovery_test.cpp b/src/mongo/db/repl/replication_recovery_test.cpp
index 84d31b48a9a..ab77100a66e 100644
--- a/src/mongo/db/repl/replication_recovery_test.cpp
+++ b/src/mongo/db/repl/replication_recovery_test.cpp
@@ -818,8 +818,7 @@ TEST_F(ReplicationRecoveryTest, RecoveryDoesNotApplyOperationsIfAppliedThroughIs
     _assertDocsInOplog(opCtx, {5});
     _assertDocsInTestCollection(opCtx, {});
     ASSERT(getConsistencyMarkers()->getOplogTruncateAfterPoint(opCtx).isNull());
-    // In 4.0 with RTT, recovering without a `recoverTimestamp` will set `appliedThrough` to the
-    // top of oplog.
+    // Recovering without a `recoverTimestamp` will set `appliedThrough` to the top of oplog.
     ASSERT_EQ(OpTime(Timestamp(5, 5), 1), getConsistencyMarkers()->getAppliedThrough(opCtx));
 }
 
diff --git a/src/mongo/db/repl/sync_tail_test_fixture.cpp b/src/mongo/db/repl/sync_tail_test_fixture.cpp
index 42036edba5d..b3b4835c860 100644
--- a/src/mongo/db/repl/sync_tail_test_fixture.cpp
+++ b/src/mongo/db/repl/sync_tail_test_fixture.cpp
@@ -133,7 +133,7 @@ void SyncTailTest::setUp() {
     // test fixture does not create a featureCompatibilityVersion document from which to initialize
     // the server parameter.
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
 }
 
 void SyncTailTest::tearDown() {
diff --git a/src/mongo/db/repl_index_build_state.h b/src/mongo/db/repl_index_build_state.h
index 363eba6eb94..94d88ce78c4 100644
--- a/src/mongo/db/repl_index_build_state.h
+++ b/src/mongo/db/repl_index_build_state.h
@@ -48,15 +48,13 @@ namespace mongo {
 // Indicates which protocol an index build is using.
 enum class IndexBuildProtocol {
     /**
-     * Refers to the pre-FCV 4.2 index build protocol for building indexes in replica sets.
-     * Index builds must complete on the primary before replicating, and are not resumable in
-     * any scenario.
+     * Refers to the legacy index build protocol for building indexes in replica sets. Index builds
+     * must complete on the primary before replicating, and are not resumable in any scenario.
      */
     kSinglePhase,
     /**
-     * Refers to the FCV 4.2 two-phase index build protocol for building indexes in replica
-     * sets. Indexes are built simultaneously on all nodes and are resumable during the draining
-     * phase.
+     * Refers to the two-phase index build protocol for building indexes in replica sets. Indexes
+     * are built simultaneously on all nodes and are resumable during the draining phase.
      */
     kTwoPhase
 };
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp b/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
index 6d9282dde0a..337f854354e 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_add_shard_test.cpp
@@ -138,7 +138,6 @@ protected:
         });
     }
 
-    // TODO: SERVER-42654
     void expectSetFeatureCompatibilityVersion(const HostAndPort& target,
                                               StatusWith<BSONObj> response,
                                               BSONObj writeConcern) {
@@ -147,7 +146,7 @@ protected:
             ASSERT_EQ(request.dbname, "admin");
             ASSERT_BSONOBJ_EQ(request.cmdObj,
                               BSON("setFeatureCompatibilityVersion"
-                                   << "4.2"
+                                   << "4.4"
                                    << "writeConcern" << writeConcern));
 
             return response;
diff --git a/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp b/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
index 225c7a25c1e..14781634e42 100644
--- a/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
+++ b/src/mongo/db/s/config/sharding_catalog_manager_shard_operations.cpp
@@ -337,16 +337,15 @@ StatusWith<ShardType> ShardingCatalogManager::_validateHostAsShard(
                                                 << "field when attempting to add "
                                                 << connectionString.toString() << " as a shard");
     }
-    // TODO: SERVER-42592
     if (serverGlobalParams.featureCompatibility.getVersion() >
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40) {
-        // If the cluster's FCV is 4.2, or upgrading to / downgrading from, the node being added
-        // must be a v4.2 binary.
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42) {
+        // If the cluster's FCV is 4.4, or upgrading to / downgrading from, the node being added
+        // must be a v4.4 binary.
         invariant(maxWireVersion == WireVersion::LATEST_WIRE_VERSION);
     } else {
-        // If the cluster's FCV is 4.0, the node being added must be a v4.0 or v4.2 binary.
+        // If the cluster's FCV is 4.2, the node being added must be a v4.2 or v4.4 binary.
         invariant(serverGlobalParams.featureCompatibility.getVersion() ==
-                  ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40);
+                  ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42);
         invariant(maxWireVersion >= WireVersion::LATEST_WIRE_VERSION - 1);
     }
 
@@ -647,27 +646,9 @@ StatusWith<std::string> ShardingCatalogManager::addShard(
 
     AddShard addShardCmd = add_shard_util::createAddShardCmd(opCtx, shardType.getName());
 
-    // TODO: SERVER-42592
-    auto addShardCmdBSON = [&]() {
-        // In 4.2, use the _addShard command to add the shard, which in turn inserts a
-        // shardIdentity document into the shard and triggers sharding state initialization.
-        // In the unlikely scenario that there's a downgrade to 4.0 between the
-        // construction of this command object and the issuing of the command
-        // on the receiving shard, the user will receive a rather harmless
-        // CommandNotFound error for _addShard, and can simply retry.
-        if (serverGlobalParams.featureCompatibility.getVersion() ==
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
-            // Needed for IDL toBSON method
-            BSONObj passthroughFields;
-            return addShardCmd.toBSON(passthroughFields);
-        } else {
-            // To support backwards compatibility with v4.0 shards, insert a shardIdentity document
-            // directly.
-            return add_shard_util::createShardIdentityUpsertForAddShard(addShardCmd);
-        }
-    }();
-
-    auto addShardStatus = runCmdOnNewShard(addShardCmdBSON);
+    // Use the _addShard command to add the shard, which in turn inserts a shardIdentity document
+    // into the shard and triggers sharding state initialization.
+    auto addShardStatus = runCmdOnNewShard(addShardCmd.toBSON({}));
 
     if (!addShardStatus.isOK()) {
         return addShardStatus;
@@ -682,19 +663,18 @@ StatusWith<std::string> ShardingCatalogManager::addShard(
         invariant(!opCtx->lockState()->isLocked());
         Lock::SharedLock lk(opCtx->lockState(), FeatureCompatibilityVersion::fcvLock);
 
-        // TODO: SERVER-42592
         BSONObj setFCVCmd;
         switch (serverGlobalParams.featureCompatibility.getVersion()) {
-            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42:
-            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo42:
+            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44:
+            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo44:
                 setFCVCmd = BSON(FeatureCompatibilityVersionCommandParser::kCommandName
-                                 << FeatureCompatibilityVersionParser::kVersion42
+                                 << FeatureCompatibilityVersionParser::kVersion44
                                  << WriteConcernOptions::kWriteConcernField
                                  << opCtx->getWriteConcern().toBSON());
                 break;
             default:
                 setFCVCmd = BSON(FeatureCompatibilityVersionCommandParser::kCommandName
-                                 << FeatureCompatibilityVersionParser::kVersion40
+                                 << FeatureCompatibilityVersionParser::kVersion42
                                  << WriteConcernOptions::kWriteConcernField
                                  << opCtx->getWriteConcern().toBSON());
                 break;
diff --git a/src/mongo/db/server_options.h b/src/mongo/db/server_options.h
index 73f49e8e150..3e82a903af8 100644
--- a/src/mongo/db/server_options.h
+++ b/src/mongo/db/server_options.h
@@ -165,40 +165,40 @@ struct ServerGlobalParams {
          *
          * The legal enum (and featureCompatibilityVersion document) states are:
          *
-         * kFullyDowngradedTo40
-         * (4.0, Unset): Only 4.0 features are available, and new and existing storage
-         *               engine entries use the 4.0 format
+         * kFullyDowngradedTo42
+         * (4.2, Unset): Only 4.2 features are available, and new and existing storage
+         *               engine entries use the 4.2 format
          *
-         * kUpgradingTo42
-         * (4.0, 4.2): Only 4.0 features are available, but new storage engine entries
-         *             use the 4.2 format, and existing entries may have either the
-         *             4.0 or 4.2 format
+         * kUpgradingTo44
+         * (4.2, 4.4): Only 4.2 features are available, but new storage engine entries
+         *             use the 4.4 format, and existing entries may have either the
+         *             4.2 or 4.4 format
          *
-         * kFullyUpgradedTo42
-         * (4.2, Unset): 4.2 features are available, and new and existing storage
-         *               engine entries use the 4.2 format
+         * kFullyUpgradedTo44
+         * (4.4, Unset): 4.4 features are available, and new and existing storage
+         *               engine entries use the 4.4 format
          *
-         * kDowngradingTo40
-         * (4.0, 4.0): Only 4.0 features are available and new storage engine
-         *             entries use the 4.0 format, but existing entries may have
-         *             either the 4.0 or 4.2 format
+         * kDowngradingTo42
+         * (4.2, 4.2): Only 4.2 features are available and new storage engine
+         *             entries use the 4.2 format, but existing entries may have
+         *             either the 4.2 or 4.4 format
          *
-         * kUnsetDefault40Behavior
+         * kUnsetDefault42Behavior
          * (Unset, Unset): This is the case on startup before the fCV document is
          *                 loaded into memory. isVersionInitialized() will return
          *                 false, and getVersion() will return the default
-         *                 (kFullyDowngradedTo40).
+         *                 (kFullyDowngradedTo42).
          *
          */
         enum class Version {
             // The order of these enums matter, higher upgrades having higher values, so that
             // features can be active or inactive if the version is higher than some minimum or
             // lower than some maximum, respectively.
-            kUnsetDefault40Behavior = 0,
-            kFullyDowngradedTo40 = 1,
-            kDowngradingTo40 = 2,
-            kUpgradingTo42 = 3,
-            kFullyUpgradedTo42 = 4,
+            kUnsetDefault42Behavior = 0,
+            kFullyDowngradedTo42 = 1,
+            kDowngradingTo42 = 2,
+            kUpgradingTo44 = 3,
+            kFullyUpgradedTo44 = 4,
         };
 
         /**
@@ -206,7 +206,7 @@ struct ServerGlobalParams {
          * exposes the actual state of the featureCompatibilityVersion if it is uninitialized.
          */
         const bool isVersionInitialized() const {
-            return _version.load() != Version::kUnsetDefault40Behavior;
+            return _version.load() != Version::kUnsetDefault42Behavior;
         }
 
         /**
@@ -226,11 +226,11 @@ struct ServerGlobalParams {
          */
         const Version getVersionUnsafe() const {
             Version v = _version.load();
-            return (v == Version::kUnsetDefault40Behavior) ? Version::kFullyDowngradedTo40 : v;
+            return (v == Version::kUnsetDefault42Behavior) ? Version::kFullyDowngradedTo42 : v;
         }
 
         void reset() {
-            _version.store(Version::kUnsetDefault40Behavior);
+            _version.store(Version::kUnsetDefault42Behavior);
         }
 
         void setVersion(Version version) {
@@ -238,12 +238,12 @@ struct ServerGlobalParams {
         }
 
         bool isVersionUpgradingOrUpgraded() {
-            return (getVersion() == Version::kUpgradingTo42 ||
-                    getVersion() == Version::kFullyUpgradedTo42);
+            return (getVersion() == Version::kUpgradingTo44 ||
+                    getVersion() == Version::kFullyUpgradedTo44);
         }
 
     private:
-        AtomicWord<Version> _version{Version::kUnsetDefault40Behavior};
+        AtomicWord<Version> _version{Version::kUnsetDefault42Behavior};
 
     } featureCompatibility;
 
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
index 8abc8da8390..d49cdfe821b 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.cpp
@@ -118,13 +118,14 @@ bool WiredTigerFileVersion::shouldDowngrade(bool readOnly,
     if (!serverGlobalParams.featureCompatibility.isVersionInitialized()) {
         // If the FCV document hasn't been read, trust the WT compatibility. MongoD will
         // downgrade to the same compatibility it discovered on startup.
-        return _startupVersion == StartupVersion::IS_40 ||
-            _startupVersion == StartupVersion::IS_36 || _startupVersion == StartupVersion::IS_34;
+        return _startupVersion == StartupVersion::IS_42 ||
+            _startupVersion == StartupVersion::IS_40 || _startupVersion == StartupVersion::IS_36 ||
+            _startupVersion == StartupVersion::IS_34;
     }
 
     if (serverGlobalParams.featureCompatibility.getVersion() !=
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo40) {
-        // Only consider downgrading when FCV is set to 4.0
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo42) {
+        // Only consider downgrading when FCV is set to 4.2
         return false;
     }
 
@@ -148,7 +149,7 @@ bool WiredTigerFileVersion::shouldDowngrade(bool readOnly,
 
 std::string WiredTigerFileVersion::getDowngradeString() {
     if (!serverGlobalParams.featureCompatibility.isVersionInitialized()) {
-        invariant(_startupVersion != StartupVersion::IS_42);
+        invariant(_startupVersion != StartupVersion::IS_44);
 
         switch (_startupVersion) {
             case StartupVersion::IS_34:
@@ -157,11 +158,13 @@ std::string WiredTigerFileVersion::getDowngradeString() {
                 return "compatibility=(release=3.0)";
             case StartupVersion::IS_40:
                 return "compatibility=(release=3.1)";
+            case StartupVersion::IS_42:
+                return "compatibility=(release=3.2)";
             default:
                 MONGO_UNREACHABLE;
         }
     }
-    return "compatibility=(release=3.1)";
+    return "compatibility=(release=3.2)";
 }
 
 using std::set;
@@ -745,7 +748,7 @@ void WiredTigerKVEngine::_openWiredTiger(const std::string& path, const std::str
 
     int ret = wiredtiger_open(path.c_str(), wtEventHandler, configStr.c_str(), &_conn);
     if (!ret) {
-        _fileVersion = {WiredTigerFileVersion::StartupVersion::IS_40};
+        _fileVersion = {WiredTigerFileVersion::StartupVersion::IS_42};
         return;
     }
 
diff --git a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.h b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.h
index 67d1ef8ba14..bb8c1e4c76c 100644
--- a/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.h
+++ b/src/mongo/db/storage/wiredtiger/wiredtiger_kv_engine.h
@@ -56,7 +56,7 @@ class WiredTigerSessionCache;
 class WiredTigerSizeStorer;
 
 struct WiredTigerFileVersion {
-    enum class StartupVersion { IS_34, IS_36, IS_40, IS_42 };
+    enum class StartupVersion { IS_34, IS_36, IS_40, IS_42, IS_44 };
 
     StartupVersion _startupVersion;
     bool shouldDowngrade(bool readOnly, bool repairMode, bool hasRecoveryTimestamp);
diff --git a/src/mongo/db/views/view_catalog.cpp b/src/mongo/db/views/view_catalog.cpp
index 6019a012b1a..a2de077d063 100644
--- a/src/mongo/db/views/view_catalog.cpp
+++ b/src/mongo/db/views/view_catalog.cpp
@@ -325,11 +325,11 @@ StatusWith<stdx::unordered_set<NamespaceString>> ViewCatalog::_validatePipeline(
     // Save this to a variable to avoid reading the atomic variable multiple times.
     auto currentFCV = serverGlobalParams.featureCompatibility.getVersion();
 
-    // If the feature compatibility version is not 4.2, and we are validating features as master,
-    // ban the use of new agg features introduced in 4.2 to prevent them from being persisted in the
+    // If the feature compatibility version is not 4.4, and we are validating features as master,
+    // ban the use of new agg features introduced in 4.4 to prevent them from being persisted in the
     // catalog.
     if (serverGlobalParams.validateFeaturesAsMaster.load() &&
-        currentFCV != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42) {
+        currentFCV != ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44) {
         expCtx->maxFeatureCompatibilityVersion = currentFCV;
     }
     auto pipelineStatus = Pipeline::parse(viewDef.pipeline(), std::move(expCtx));
diff --git a/src/mongo/db/wire_version.h b/src/mongo/db/wire_version.h
index 8ecb08fd7dd..561070f2a1c 100644
--- a/src/mongo/db/wire_version.h
+++ b/src/mongo/db/wire_version.h
@@ -76,9 +76,12 @@ enum WireVersion {
     // Supports sharded transactions (4.2+).
     SHARDED_TRANSACTIONS = 8,
 
+    // TODO SERVER-42985: Supports some upcoming feature (4.4+).
+    PLACEHOLDER_FOR_44 = 9,
+
     // Set this to the highest value in this enum - it will be the default maxWireVersion for
     // the WireSpec values.
-    LATEST_WIRE_VERSION = SHARDED_TRANSACTIONS,
+    LATEST_WIRE_VERSION = PLACEHOLDER_FOR_44,
 };
 
 /**
diff --git a/src/mongo/dbtests/dbtests.cpp b/src/mongo/dbtests/dbtests.cpp
index 942678a87dd..62238c52cf7 100644
--- a/src/mongo/dbtests/dbtests.cpp
+++ b/src/mongo/dbtests/dbtests.cpp
@@ -182,7 +182,7 @@ int dbtestsMain(int argc, char** argv, char** envp) {
 
     mongo::runGlobalInitializersOrDie(argc, argv, envp);
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
     repl::ReplSettings replSettings;
     replSettings.setOplogSizeBytes(10 * 1024 * 1024);
     setGlobalServiceContext(ServiceContext::make());
diff --git a/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp b/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp
index 570551c7352..aff4f4214d8 100644
--- a/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp
+++ b/src/mongo/s/commands/cluster_set_feature_compatibility_version_cmd.cpp
@@ -70,14 +70,14 @@ public:
     }
 
     std::string help() const override {
+        using FCVP = FeatureCompatibilityVersionParser;
         return str::stream()
-            << "Set the API version for the cluster. If set to \""
-            << FeatureCompatibilityVersionParser::kVersion40
-            << "\", then 4.2 features are disabled. If \""
-            << FeatureCompatibilityVersionParser::kVersion42
-            << "\", then 4.2 features are enabled, and all nodes in the cluster must be version "
-            << "4.2. See " << feature_compatibility_version_documentation::kCompatibilityLink
-            << ".";
+            << "Set the API version used by this cluster. If set to '" << FCVP::kVersion42
+            << "', then " << FCVP::kVersion44 << " features are disabled. If set to '"
+            << FCVP::kVersion44 << "', then " << FCVP::kVersion44
+            << " features are enabled, and all nodes in the cluster must be binary version "
+            << FCVP::kVersion44 << ". See "
+            << feature_compatibility_version_documentation::kCompatibilityLink << ".";
     }
 
     Status checkAuthForCommand(Client* client,
diff --git a/src/mongo/s/server.cpp b/src/mongo/s/server.cpp
index c94bb38f2e9..92282a63a73 100644
--- a/src/mongo/s/server.cpp
+++ b/src/mongo/s/server.cpp
@@ -679,10 +679,11 @@ MONGO_INITIALIZER_GENERAL(ForkServer, ("EndStartupOptionHandling"), ("default"))
 // to the latest version because there is no feature gating that currently occurs at the mongos
 // level. The shards are responsible for rejecting usages of new features if their
 // featureCompatibilityVersion is lower.
-MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersion42, ("EndStartupOptionStorage"))
+MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersionLatest,
+                                     ("EndStartupOptionStorage"))
 (InitializerContext* context) {
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
     return Status::OK();
 }
 
diff --git a/src/mongo/s/sharding_mongod_test_fixture.cpp b/src/mongo/s/sharding_mongod_test_fixture.cpp
index 2a427e29b09..7d7b8419e58 100644
--- a/src/mongo/s/sharding_mongod_test_fixture.cpp
+++ b/src/mongo/s/sharding_mongod_test_fixture.cpp
@@ -144,11 +144,10 @@ void ShardingMongodTestFixture::setUp() {
     repl::setOplogCollectionName(service);
     repl::createOplog(_opCtx.get());
 
-    // TODO: SERVER-42592
     // Set the highest FCV because otherwise it defaults to the lower FCV. This way we default to
     // testing this release's code, not backwards compatibility code.
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
 }
 
 std::unique_ptr<ReplicationCoordinatorMock> ShardingMongodTestFixture::makeReplicationCoordinator(
diff --git a/src/mongo/shell/dbshell.cpp b/src/mongo/shell/dbshell.cpp
index 12911840cb9..bb39c1d4060 100644
--- a/src/mongo/shell/dbshell.cpp
+++ b/src/mongo/shell/dbshell.cpp
@@ -99,10 +99,11 @@ const std::string kDefaultMongoURL = "mongodb://"s + kDefaultMongoHost + ":"s +
 // to the latest version because there is no feature gating that currently occurs at the mongo shell
 // level. The server is responsible for rejecting usages of new features if its
 // featureCompatibilityVersion is lower.
-MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersion42, ("EndStartupOptionSetup"))
+MONGO_INITIALIZER_WITH_PREREQUISITES(SetFeatureCompatibilityVersionLatest,
+                                     ("EndStartupOptionSetup"))
 (InitializerContext* context) {
     mongo::serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
     return Status::OK();
 }
 
diff --git a/src/mongo/shell/shardingtest.js b/src/mongo/shell/shardingtest.js
index 8ada418abea..d31bab4ebee 100644
--- a/src/mongo/shell/shardingtest.js
+++ b/src/mongo/shell/shardingtest.js
@@ -1467,7 +1467,7 @@ var ShardingTest = function(params) {
     const configRS = this.configRS;
     if (_hasNewFeatureCompatibilityVersion() && _isMixedVersionCluster()) {
         function setFeatureCompatibilityVersion() {
-            assert.commandWorked(csrsPrimary.adminCommand({setFeatureCompatibilityVersion: '4.0'}));
+            assert.commandWorked(csrsPrimary.adminCommand({setFeatureCompatibilityVersion: '4.2'}));
 
             // Wait for the new featureCompatibilityVersion to propagate to all nodes in the CSRS
             // to ensure that older versions of mongos can successfully connect.
diff --git a/src/mongo/unittest/unittest.cpp b/src/mongo/unittest/unittest.cpp
index 3cce9bf868d..1aee738eb4a 100644
--- a/src/mongo/unittest/unittest.cpp
+++ b/src/mongo/unittest/unittest.cpp
@@ -169,7 +169,7 @@ UnsafeScopeGuard<F> MakeUnsafeScopeGuard(F fun) {
 // with a meaningful value will trigger failures as of SERVER-32630.
 void setUpFCV() {
     serverGlobalParams.featureCompatibility.setVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo42);
+        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo44);
 }
 void tearDownFCV() {
     serverGlobalParams.featureCompatibility.reset();