SERVER-49063: Update FCV 4.6 constants to 4.5.1

23 files changed, 95 insertions, 94 deletions

diff --git a/buildscripts/resmokelib/multiversionconstants.py b/buildscripts/resmokelib/multiversionconstants.py
index 3d0bf83debc..4a524c5f0b4 100644
--- a/buildscripts/resmokelib/multiversionconstants.py
+++ b/buildscripts/resmokelib/multiversionconstants.py
@@ -2,7 +2,7 @@
 
 LAST_STABLE_BIN_VERSION = "4.4"
 LAST_STABLE_FCV = "4.4"
-LATEST_FCV = "4.6"
+LATEST_FCV = "4.5.1"
 
 LAST_STABLE_MONGO_BINARY = "mongo-" + LAST_STABLE_BIN_VERSION
 LAST_STABLE_MONGOD_BINARY = "mongod-" + LAST_STABLE_BIN_VERSION
diff --git a/jstests/multiVersion/genericSetFCVUsage/major_version_upgrade.js b/jstests/multiVersion/genericSetFCVUsage/major_version_upgrade.js
index b98384287d6..2975a91f58e 100644
--- a/jstests/multiVersion/genericSetFCVUsage/major_version_upgrade.js
+++ b/jstests/multiVersion/genericSetFCVUsage/major_version_upgrade.js
@@ -38,7 +38,7 @@ const versions = [
     {binVersion: '4.2', featureCompatibilityVersion: '4.2', testCollection: 'four_two'},
     {binVersion: '4.4', featureCompatibilityVersion: '4.4', testCollection: 'four_four'},
     {binVersion: 'last-stable', testCollection: 'last_stable'},
-    {binVersion: 'latest', featureCompatibilityVersion: '4.6', testCollection: 'latest'},
+    {binVersion: 'latest', featureCompatibilityVersion: '4.5.1', testCollection: 'latest'},
 ];
 
 // These key patterns are considered valid for existing v:0 and v:1 indexes, but are considered
diff --git a/src/mongo/db/commands/feature_compatibility_version.cpp b/src/mongo/db/commands/feature_compatibility_version.cpp
index 9401cc7f0f1..5c96789c300 100644
--- a/src/mongo/db/commands/feature_compatibility_version.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version.cpp
@@ -72,7 +72,7 @@ void FeatureCompatibilityVersion::setTargetUpgrade(OperationContext* opCtx) {
         updateMods.append(FeatureCompatibilityVersionParser::kVersionField,
                           FeatureCompatibilityVersionParser::kVersion44);
         updateMods.append(FeatureCompatibilityVersionParser::kTargetVersionField,
-                          FeatureCompatibilityVersionParser::kVersion46);
+                          FeatureCompatibilityVersionParser::kVersion451);
     });
 }
 
@@ -125,7 +125,7 @@ void FeatureCompatibilityVersion::setIfCleanStartup(OperationContext* opCtx,
         repl::TimestampedBSONObj{
             BSON("_id" << FeatureCompatibilityVersionParser::kParameterName
                        << FeatureCompatibilityVersionParser::kVersionField
-                       << (storeUpgradeVersion ? FeatureCompatibilityVersionParser::kVersion46
+                       << (storeUpgradeVersion ? FeatureCompatibilityVersionParser::kVersion451
                                                : FeatureCompatibilityVersionParser::kVersion44)),
             Timestamp()},
         repl::OpTime::kUninitializedTerm));  // No timestamp or term because this write is not
@@ -176,8 +176,8 @@ void FeatureCompatibilityVersion::updateMinWireVersion() {
 
     switch (serverGlobalParams.featureCompatibility.getVersion()) {
         case ServerGlobalParams::FeatureCompatibility::kLatest:
-        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46:
-        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo44:
+        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451:
+        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingFrom451To44:
             spec.incomingInternalClient.minWireVersion = LATEST_WIRE_VERSION;
             spec.outgoing.minWireVersion = LATEST_WIRE_VERSION;
             return;
@@ -229,7 +229,7 @@ void FeatureCompatibilityVersion::_setVersion(
     // 2. Setting featureCompatibilityVersion from fullyDowngraded to upgrading.
     const auto shouldIncrementTopologyVersion =
         newVersion == ServerGlobalParams::FeatureCompatibility::kLastLTS ||
-        newVersion == ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46;
+        newVersion == ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451;
     if (isReplSet && shouldIncrementTopologyVersion) {
         replCoordinator->incrementTopologyVersion();
     }
@@ -257,10 +257,10 @@ void FeatureCompatibilityVersion::onReplicationRollback(OperationContext* opCtx)
 void FeatureCompatibilityVersion::_validateVersion(StringData version) {
     uassert(40284,
             str::stream() << "featureCompatibilityVersion must be '"
-                          << FeatureCompatibilityVersionParser::kVersion46 << "' or '"
+                          << FeatureCompatibilityVersionParser::kVersion451 << "' or '"
                           << FeatureCompatibilityVersionParser::kVersion44 << "'. See "
                           << feature_compatibility_version_documentation::kCompatibilityLink << ".",
-            version == FeatureCompatibilityVersionParser::kVersion46 ||
+            version == FeatureCompatibilityVersionParser::kVersion451 ||
                 version == FeatureCompatibilityVersionParser::kVersion44);
 }
 
@@ -320,17 +320,17 @@ void FeatureCompatibilityVersionParameter::append(OperationContext* opCtx,
         case ServerGlobalParams::FeatureCompatibility::kLatest:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
-                FeatureCompatibilityVersionParser::kVersion46);
+                FeatureCompatibilityVersionParser::kVersion451);
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46:
+        case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
                 FeatureCompatibilityVersionParser::kVersion44);
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kTargetVersionField,
-                FeatureCompatibilityVersionParser::kVersion46);
+                FeatureCompatibilityVersionParser::kVersion451);
             return;
-        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo44:
+        case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingFrom451To44:
             featureCompatibilityVersionBuilder.append(
                 FeatureCompatibilityVersionParser::kVersionField,
                 FeatureCompatibilityVersionParser::kVersion44);
diff --git a/src/mongo/db/commands/feature_compatibility_version.h b/src/mongo/db/commands/feature_compatibility_version.h
index d1058ae57e9..f4d0263f029 100644
--- a/src/mongo/db/commands/feature_compatibility_version.h
+++ b/src/mongo/db/commands/feature_compatibility_version.h
@@ -52,23 +52,23 @@ public:
     static Lock::ResourceMutex fcvLock;
 
     /**
-     * Records intent to perform a 4.4 -> 4.6 upgrade by updating the on-disk feature
-     * compatibility version document to have 'version'=4.4, 'targetVersion'=4.6.
+     * Records intent to perform a 4.4 -> 4.5.1 upgrade by updating the on-disk feature
+     * compatibility version document to have 'version'=4.4, 'targetVersion'=4.5.1.
      * Should be called before schemas are modified.
      */
     static void setTargetUpgrade(OperationContext* opCtx);
 
     /**
-     * Records intent to perform a 4.6 -> 4.4 downgrade by updating the on-disk feature
+     * Records intent to perform a 4.5.1 -> 4.4 downgrade by updating the on-disk feature
      * compatibility version document to have 'version'=4.4, 'targetVersion'=4.4.
      * Should be called before schemas are modified.
      */
     static void setTargetDowngrade(OperationContext* opCtx);
 
     /**
-     * Records the completion of a 4.4 <-> 4.6 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.
+     * Records the completion of a 4.4 <-> 4.5.1 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.
      */
     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 021fdf03d07..27b35a3513b 100644
--- a/src/mongo/db/commands/feature_compatibility_version_command_parser.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version_command_parser.cpp
@@ -77,11 +77,11 @@ StatusWith<std::string> FeatureCompatibilityVersionCommandParser::extractVersion
 
     const std::string version = versionElem.String();
 
-    if (version != FeatureCompatibilityVersionParser::kVersion46 &&
+    if (version != FeatureCompatibilityVersionParser::kVersion451 &&
         version != FeatureCompatibilityVersionParser::kVersion44) {
         return {ErrorCodes::BadValue,
                 str::stream() << "Invalid command argument. Expected '"
-                              << FeatureCompatibilityVersionParser::kVersion46 << "' or '"
+                              << FeatureCompatibilityVersionParser::kVersion451 << "' or '"
                               << FeatureCompatibilityVersionParser::kVersion44 << "', 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 a0a2ead7bea..97fc21eb67e 100644
--- a/src/mongo/db/commands/feature_compatibility_version_parser.cpp
+++ b/src/mongo/db/commands/feature_compatibility_version_parser.cpp
@@ -39,9 +39,9 @@
 namespace mongo {
 
 constexpr StringData FeatureCompatibilityVersionParser::kVersion44;
-constexpr StringData FeatureCompatibilityVersionParser::kVersion46;
-constexpr StringData FeatureCompatibilityVersionParser::kVersionDowngradingTo44;
-constexpr StringData FeatureCompatibilityVersionParser::kVersionUpgradingTo46;
+constexpr StringData FeatureCompatibilityVersionParser::kVersion451;
+constexpr StringData FeatureCompatibilityVersionParser::kVersionDowngradingFrom451To44;
+constexpr StringData FeatureCompatibilityVersionParser::kVersionUpgradingFrom44To451;
 constexpr StringData FeatureCompatibilityVersionParser::kVersionUnset;
 
 constexpr StringData FeatureCompatibilityVersionParser::kParameterName;
@@ -72,11 +72,11 @@ FeatureCompatibilityVersionParser::parse(const BSONObj& featureCompatibilityVers
                                   << ".");
             }
 
-            if (elem.String() != kVersion46 && elem.String() != kVersion44) {
+            if (elem.String() != kVersion451 && elem.String() != kVersion44) {
                 return Status(ErrorCodes::BadValue,
                               str::stream()
                                   << "Invalid value for " << fieldName << ", found "
-                                  << elem.String() << ", expected '" << kVersion46 << "' or '"
+                                  << elem.String() << ", expected '" << kVersion451 << "' or '"
                                   << kVersion44 << "'. Contents of " << kParameterName
                                   << " document in "
                                   << NamespaceString::kServerConfigurationNamespace.toString()
@@ -103,15 +103,15 @@ FeatureCompatibilityVersionParser::parse(const BSONObj& featureCompatibilityVers
     }
 
     if (versionString == kVersion44) {
-        if (targetVersionString == kVersion46) {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46;
+        if (targetVersionString == kVersion451) {
+            version = ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451;
         } else if (targetVersionString == kVersion44) {
-            version = ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo44;
+            version = ServerGlobalParams::FeatureCompatibility::Version::kDowngradingFrom451To44;
         } else {
             version = ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo44;
         }
-    } else if (versionString == kVersion46) {
-        if (targetVersionString == kVersion46 || targetVersionString == kVersion44) {
+    } else if (versionString == kVersion451) {
+        if (targetVersionString == kVersion451 || targetVersionString == kVersion44) {
             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::kFullyUpgradedTo46;
+            version = ServerGlobalParams::FeatureCompatibility::Version::kVersion451;
         }
     } 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 e52e73e4477..01f25fe6f5d 100644
--- a/src/mongo/db/commands/feature_compatibility_version_parser.h
+++ b/src/mongo/db/commands/feature_compatibility_version_parser.h
@@ -41,9 +41,9 @@ namespace mongo {
 class FeatureCompatibilityVersionParser {
 public:
     static constexpr StringData kVersion44 = "4.4"_sd;
-    static constexpr StringData kVersion46 = "4.6"_sd;
-    static constexpr StringData kVersionDowngradingTo44 = "downgrading to 4.4"_sd;
-    static constexpr StringData kVersionUpgradingTo46 = "upgrading to 4.6"_sd;
+    static constexpr StringData kVersion451 = "4.5.1"_sd;
+    static constexpr StringData kVersionDowngradingFrom451To44 = "downgrading from 4.5.1 to 4.4"_sd;
+    static constexpr StringData kVersionUpgradingFrom44To451 = "upgrading from 4.4 to 4.5.1"_sd;
     static constexpr StringData kVersionUnset = "Unset"_sd;
 
     static constexpr StringData kParameterName = "featureCompatibilityVersion"_sd;
@@ -67,12 +67,12 @@ public:
                 return kVersionUnset;
             case ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo44:
                 return kVersion44;
-            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46:
-                return kVersionUpgradingTo46;
-            case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo44:
-                return kVersionDowngradingTo44;
-            case ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46:
-                return kVersion46;
+            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451:
+                return kVersionUpgradingFrom44To451;
+            case ServerGlobalParams::FeatureCompatibility::Version::kDowngradingFrom451To44:
+                return kVersionDowngradingFrom451To44;
+            case ServerGlobalParams::FeatureCompatibility::Version::kVersion451:
+                return kVersion451;
             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 7f5e2a6400e..f34a64d157c 100644
--- a/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
+++ b/src/mongo/db/commands/set_feature_compatibility_version_command.cpp
@@ -93,8 +93,8 @@ void deletePersistedDefaultRWConcernDocument(OperationContext* opCtx) {
 }
 
 /**
- * Sets the minimum allowed version for the cluster. If it is 4.4, then the node should not use 4.6
- * features.
+ * Sets the minimum allowed version for the cluster. If it is 4.4, then the node should not
+ * use 4.5.1 features.
  *
  * Format:
  * {
@@ -121,11 +121,12 @@ public:
     std::string help() const override {
         using FCVP = FeatureCompatibilityVersionParser;
         std::stringstream h;
-        h << "Set the API version exposed by this node. If set to '" << FCVP::kVersion44
-          << "', then " << FCVP::kVersion46 << " features are disabled. If set to '"
-          << FCVP::kVersion46 << "', then " << FCVP::kVersion46
+        h << "Set the featureCompatibilityVersion exposed by this node. If set to '"
+          << FCVP::kVersion44 << "', then " << FCVP::kVersion451
+          << " features are disabled. If set to '" << FCVP::kVersion451 << "', then "
+          << FCVP::kVersion451
           << " features are enabled, and all nodes in the cluster must be binary version "
-          << FCVP::kVersion46 << ". See "
+          << FCVP::kVersion451 << ". See "
           << feature_compatibility_version_documentation::kCompatibilityLink << ".";
         return h.str();
     }
@@ -183,16 +184,15 @@ public:
         ServerGlobalParams::FeatureCompatibility::Version actualVersion =
             serverGlobalParams.featureCompatibility.getVersion();
 
-        if (requestedVersion == FeatureCompatibilityVersionParser::kVersion46) {
+        if (requestedVersion == FeatureCompatibilityVersionParser::kVersion451) {
             uassert(ErrorCodes::IllegalOperation,
-                    "cannot initiate featureCompatibilityVersion upgrade to 4.6 while a previous "
+                    "cannot initiate featureCompatibilityVersion upgrade to 4.5.1 while a previous "
                     "featureCompatibilityVersion downgrade to 4.4 has not completed. Finish "
-                    "downgrade to 4.4, then upgrade to 4.6.",
+                    "downgrade to 4.4, then upgrade to 4.5.1.",
                     actualVersion !=
-                        ServerGlobalParams::FeatureCompatibility::Version::kDowngradingTo44);
+                        ServerGlobalParams::FeatureCompatibility::Version::kDowngradingFrom451To44);
 
-            if (actualVersion ==
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46) {
+            if (actualVersion == ServerGlobalParams::FeatureCompatibility::Version::kVersion451) {
                 // Set the client's last opTime to the system last opTime so no-ops wait for
                 // writeConcern.
                 repl::ReplClientInfo::forClient(opCtx->getClient())
@@ -206,7 +206,7 @@ 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 4.6 FCV and act accordingly.
+                //     upgrading to 4.5.1 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.
@@ -241,9 +241,9 @@ public:
         } else if (requestedVersion == FeatureCompatibilityVersionParser::kVersion44) {
             uassert(ErrorCodes::IllegalOperation,
                     "cannot initiate setting featureCompatibilityVersion to 4.4 while a previous "
-                    "featureCompatibilityVersion upgrade to 4.6 has not completed.",
+                    "featureCompatibilityVersion upgrade to 4.5.1 has not completed.",
                     actualVersion !=
-                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46);
+                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451);
 
             if (actualVersion ==
                 ServerGlobalParams::FeatureCompatibility::Version::kFullyDowngradedTo44) {
diff --git a/src/mongo/db/index/index_descriptor.cpp b/src/mongo/db/index/index_descriptor.cpp
index 7c16ae58040..55e8ec0eb8c 100644
--- a/src/mongo/db/index/index_descriptor.cpp
+++ b/src/mongo/db/index/index_descriptor.cpp
@@ -180,7 +180,7 @@ IndexDescriptor::Comparison IndexDescriptor::compareIndexOptions(
     // The partialFilterExpression is only part of the index signature if FCV has been set to 4.6.
     // TODO SERVER-47766: remove these FCV checks after we branch for 4.7.
     auto isFCV46 = serverGlobalParams.featureCompatibility.isVersion(
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46);
+        ServerGlobalParams::FeatureCompatibility::Version::kVersion451);
 
     // If we have a partial filter expression and the other index doesn't, or vice-versa, then the
     // two indexes are not equivalent. We therefore return Comparison::kDifferent immediately.
diff --git a/src/mongo/db/mongod_main.cpp b/src/mongo/db/mongod_main.cpp
index fe91a5478fc..368c7605491 100644
--- a/src/mongo/db/mongod_main.cpp
+++ b/src/mongo/db/mongod_main.cpp
@@ -1084,7 +1084,7 @@ void shutdownTask(const ShutdownTaskArgs& shutdownArgs) {
 
     // TODO SERVER-49138: Remove this FCV check once we branch for 4.8.
     if (serverGlobalParams.featureCompatibility.isVersion(
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46)) {
+            ServerGlobalParams::FeatureCompatibility::Version::kVersion451)) {
         if (auto replCoord = repl::ReplicationCoordinator::get(serviceContext);
             replCoord && replCoord->enterQuiesceModeIfSecondary(shutdownTimeout)) {
             ServiceContext::UniqueOperationContext uniqueOpCtx;
diff --git a/src/mongo/db/repair_database_and_check_version.cpp b/src/mongo/db/repair_database_and_check_version.cpp
index 8d959ee2bd1..b7a56e42764 100644
--- a/src/mongo/db/repair_database_and_check_version.cpp
+++ b/src/mongo/db/repair_database_and_check_version.cpp
@@ -77,7 +77,7 @@ namespace {
 
 const std::string mustDowngradeErrorMsg = str::stream()
     << "UPGRADE PROBLEM: The data files need to be fully upgraded to version 4.4 before attempting "
-       "an upgrade to 4.6; see "
+       "an upgrade to 4.5.1; see "
     << feature_compatibility_version_documentation::kUpgradeLink << " for more details.";
 
 Status restoreMissingFeatureCompatibilityVersionDocument(OperationContext* opCtx,
@@ -584,22 +584,22 @@ bool repairDatabasesAndCheckVersion(OperationContext* opCtx) {
                     // On startup, if the version is in an upgrading or downgrading state, print a
                     // warning.
                     if (version ==
-                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46) {
+                        ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451) {
                         LOGV2_WARNING_OPTIONS(
                             21011,
                             {logv2::LogTag::kStartupWarnings},
                             "A featureCompatibilityVersion upgrade did not complete. The current "
                             "featureCompatibilityVersion is "
                             "{currentfeatureCompatibilityVersion}. To fix this, use the "
-                            "setFeatureCompatibilityVersion command to resume upgrade to 4.6.",
+                            "setFeatureCompatibilityVersion command to resume upgrade to 4.5.1.",
                             "A featureCompatibilityVersion upgrade did not complete. To fix this, "
                             "use the "
-                            "setFeatureCompatibilityVersion command to resume upgrade to 4.6",
+                            "setFeatureCompatibilityVersion command to resume upgrade to 4.5.1",
                             "currentfeatureCompatibilityVersion"_attr =
                                 FeatureCompatibilityVersionParser::toString(version));
                     } else if (version ==
                                ServerGlobalParams::FeatureCompatibility::Version::
-                                   kDowngradingTo44) {
+                                   kDowngradingFrom451To44) {
                         LOGV2_WARNING_OPTIONS(
                             21014,
                             {logv2::LogTag::kStartupWarnings},
diff --git a/src/mongo/db/repl/initial_syncer_test.cpp b/src/mongo/db/repl/initial_syncer_test.cpp
index 6b7138aaa8e..9ea641dfc5a 100644
--- a/src/mongo/db/repl/initial_syncer_test.cpp
+++ b/src/mongo/db/repl/initial_syncer_test.cpp
@@ -1905,7 +1905,7 @@ TEST_F(InitialSyncerTest,
        InitialSyncerReturnsIncompatibleServerVersionWhenFCVFetcherReturnsUpgradeTargetVersion) {
     auto docs = {BSON("_id" << FeatureCompatibilityVersionParser::kParameterName << "version"
                             << FeatureCompatibilityVersionParser::kVersion44 << "targetVersion"
-                            << FeatureCompatibilityVersionParser::kVersion46)};
+                            << FeatureCompatibilityVersionParser::kVersion451)};
     runInitialSyncWithBadFCVResponse(docs, ErrorCodes::IncompatibleServerVersion);
 }
 
diff --git a/src/mongo/db/repl/repl_set_heartbeat_args_v1.cpp b/src/mongo/db/repl/repl_set_heartbeat_args_v1.cpp
index 92d0dd799c6..c1bc9b7ac83 100644
--- a/src/mongo/db/repl/repl_set_heartbeat_args_v1.cpp
+++ b/src/mongo/db/repl/repl_set_heartbeat_args_v1.cpp
@@ -178,8 +178,9 @@ void ReplSetHeartbeatArgsV1::addToBSON(BSONObjBuilder* builder) const {
     builder->appendIntOrLL(kSenderIdFieldName, _senderId);
     builder->appendIntOrLL(kTermFieldName, _term);
 
+    // TODO SERVER-49382: Remove this FCV check after we branch for 4.7.
     if (serverGlobalParams.featureCompatibility.isVersion(
-            ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46)) {
+            ServerGlobalParams::FeatureCompatibility::Version::kVersion451)) {
         builder->append(kPrimaryIdFieldName, _primaryId);
     }
 }
diff --git a/src/mongo/db/repl/replication_coordinator_impl.cpp b/src/mongo/db/repl/replication_coordinator_impl.cpp
index 7299ba08b03..c058325362e 100644
--- a/src/mongo/db/repl/replication_coordinator_impl.cpp
+++ b/src/mongo/db/repl/replication_coordinator_impl.cpp
@@ -3198,7 +3198,7 @@ bool ReplicationCoordinatorImpl::_supportsAutomaticReconfig() const {
     }
 
     if (serverGlobalParams.featureCompatibility.getVersion() !=
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46) {
+        ServerGlobalParams::FeatureCompatibility::Version::kVersion451) {
         return false;
     }
 
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 3b6a9b7da00..29e0011b2c1 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
@@ -139,7 +139,7 @@ protected:
             ASSERT_EQ(request.dbname, "admin");
             ASSERT_BSONOBJ_EQ(request.cmdObj,
                               BSON("setFeatureCompatibilityVersion"
-                                   << "4.6"
+                                   << "4.5.1"
                                    << "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 15792b5239e..5978639a12b 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
@@ -653,9 +653,9 @@ StatusWith<std::string> ShardingCatalogManager::addShard(
         BSONObj setFCVCmd;
         switch (serverGlobalParams.featureCompatibility.getVersion()) {
             case ServerGlobalParams::FeatureCompatibility::kLatest:
-            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingTo46:
+            case ServerGlobalParams::FeatureCompatibility::Version::kUpgradingFrom44To451:
                 setFCVCmd = BSON(FeatureCompatibilityVersionCommandParser::kCommandName
-                                 << FeatureCompatibilityVersionParser::kVersion46
+                                 << FeatureCompatibilityVersionParser::kVersion451
                                  << WriteConcernOptions::kWriteConcernField
                                  << opCtx->getWriteConcern().toBSON());
                 break;
diff --git a/src/mongo/db/server_options.h b/src/mongo/db/server_options.h
index fb241af8e0a..3be5400522a 100644
--- a/src/mongo/db/server_options.h
+++ b/src/mongo/db/server_options.h
@@ -166,19 +166,19 @@ struct ServerGlobalParams {
          * (4.4, Unset): Only 4.4 features are available, and new and existing storage
          *               engine entries use the 4.4 format
          *
-         * kUpgradingTo46
-         * (4.4, 4.6): Only 4.4 features are available, but new storage engine entries
-         *             use the 4.6 format, and existing entries may have either the
-         *             4.4 or 4.6 format
+         * kUpgradingFrom44To451
+         * (4.4, 4.5.1): Only 4.4 features are available, but new storage engine entries
+         *             use the 4.5.1 format, and existing entries may have either the
+         *             4.4 or 4.5.1 format
          *
-         * kFullyUpgradedTo46
-         * (4.6, Unset): 4.6 features are available, and new and existing storage
-         *               engine entries use the 4.6 format
+         * kVersion451
+         * (4.5.1, Unset): 4.5.1 features are available, and new and existing storage
+         *               engine entries use the 4.5.1 format
          *
-         * kDowngradingTo44
+         * kDowngradingFrom451To44
          * (4.4, 4.4): Only 4.4 features are available and new storage engine
          *             entries use the 4.4 format, but existing entries may have
-         *             either the 4.4 or 4.6 format
+         *             either the 4.4 or 4.5.1 format
          *
          * kUnsetDefault44Behavior
          * (Unset, Unset): This is the case on startup before the fCV document is
@@ -193,12 +193,12 @@ struct ServerGlobalParams {
             // lower than some maximum, respectively.
             kUnsetDefault44Behavior = 0,
             kFullyDowngradedTo44 = 1,
-            kDowngradingTo44 = 2,
-            kUpgradingTo46 = 3,
-            kFullyUpgradedTo46 = 4,
+            kDowngradingFrom451To44 = 2,
+            kUpgradingFrom44To451 = 3,
+            kVersion451 = 4,
         };
 
-        static constexpr Version kLatest = Version::kFullyUpgradedTo46;
+        static constexpr Version kLatest = Version::kVersion451;
         static constexpr Version kLastContinuous = Version::kFullyDowngradedTo44;
         static constexpr Version kLastLTS = Version::kFullyDowngradedTo44;
 
diff --git a/src/mongo/db/storage/storage_engine_impl.cpp b/src/mongo/db/storage/storage_engine_impl.cpp
index ce7b5c711c3..bcded20bb6d 100644
--- a/src/mongo/db/storage/storage_engine_impl.cpp
+++ b/src/mongo/db/storage/storage_engine_impl.cpp
@@ -860,7 +860,7 @@ bool StorageEngineImpl::supportsResumableIndexBuilds() const {
     return enableResumableIndexBuilds && supportsReadConcernMajority() && !isEphemeral() &&
         serverGlobalParams.featureCompatibility.isVersionInitialized() &&
         serverGlobalParams.featureCompatibility.getVersion() ==
-        ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46 &&
+        ServerGlobalParams::FeatureCompatibility::Version::kVersion451 &&
         !repl::ReplSettings::shouldRecoverFromOplogAsStandalone();
 }
 
diff --git a/src/mongo/db/vector_clock.cpp b/src/mongo/db/vector_clock.cpp
index 5991ba97671..5ea6b280bed 100644
--- a/src/mongo/db/vector_clock.cpp
+++ b/src/mongo/db/vector_clock.cpp
@@ -159,8 +159,7 @@ public:
              Component component) const override {
         const auto& fcv = serverGlobalParams.featureCompatibility;
         if (fcv.isVersionInitialized() &&
-            fcv.getVersion() ==
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46) {
+            fcv.getVersion() == ServerGlobalParams::FeatureCompatibility::Version::kVersion451) {
             return ActualFormat::out(service, opCtx, permitRefresh, out, time, component);
         }
         return false;
diff --git a/src/mongo/db/wire_version.h b/src/mongo/db/wire_version.h
index 35244b7ddda..6e9403cf714 100644
--- a/src/mongo/db/wire_version.h
+++ b/src/mongo/db/wire_version.h
@@ -79,12 +79,12 @@ enum WireVersion {
     // Supports resumable initial sync (4.4+).
     RESUMABLE_INITIAL_SYNC = 9,
 
-    // Supports features available from 4.6 and onwards.
-    WIRE_VERSION_46 = 10,
+    // Supports features available from 4.5.1 and onwards.
+    WIRE_VERSION_451 = 10,
 
     // Set this to the highest value in this enum - it will be the default maxWireVersion for
     // the WireSpec values.
-    LATEST_WIRE_VERSION = WIRE_VERSION_46,
+    LATEST_WIRE_VERSION = WIRE_VERSION_451,
 };
 
 /**
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 51823aec2be..ab77d891cd8 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
@@ -72,11 +72,12 @@ public:
     std::string help() const override {
         using FCVP = FeatureCompatibilityVersionParser;
         return str::stream()
-            << "Set the API version used by this cluster. If set to '" << FCVP::kVersion44
-            << "', then " << FCVP::kVersion46 << " features are disabled. If set to '"
-            << FCVP::kVersion46 << "', then " << FCVP::kVersion46
+            << "Set the featureCompatibilityVersion used by this cluster. If set to '"
+            << FCVP::kVersion44 << "', then " << FCVP::kVersion451
+            << " features are disabled. If set to '" << FCVP::kVersion451 << "', then "
+            << FCVP::kVersion451
             << " features are enabled, and all nodes in the cluster must be binary version "
-            << FCVP::kVersion46 << ". See "
+            << FCVP::kVersion451 << ". See "
             << feature_compatibility_version_documentation::kCompatibilityLink << ".";
     }
 
diff --git a/src/mongo/s/mongos_main.cpp b/src/mongo/s/mongos_main.cpp
index e6a91259662..e60aaf53fdb 100644
--- a/src/mongo/s/mongos_main.cpp
+++ b/src/mongo/s/mongos_main.cpp
@@ -290,7 +290,7 @@ void cleanupTask(const ShutdownTaskArgs& shutdownArgs) {
         //
         // TODO SERVER-49138: Remove this FCV check once we branch for 4.8.
         if (serverGlobalParams.featureCompatibility.isVersion(
-                ServerGlobalParams::FeatureCompatibility::Version::kFullyUpgradedTo46);
+                ServerGlobalParams::FeatureCompatibility::Version::kVersion451);
             auto mongosTopCoord = MongosTopologyCoordinator::get(opCtx)) {
             mongosTopCoord->enterQuiesceModeAndWait(opCtx, quiesceTime);
         }
diff --git a/src/mongo/shell/feature_compatibility_version.js b/src/mongo/shell/feature_compatibility_version.js
index d5deffaf170..b014a3b90d5 100644
--- a/src/mongo/shell/feature_compatibility_version.js
+++ b/src/mongo/shell/feature_compatibility_version.js
@@ -10,7 +10,7 @@
  * multiple times.
  */
 
-var latestFCV = "4.6";
+var latestFCV = "4.5.1";
 var lastStableFCV = "4.4";
 
 /**