diff --git a/quic/api/QuicTransportBase.cpp b/quic/api/QuicTransportBase.cpp
index a964c5eca..9c2cfd861 100644
--- a/quic/api/QuicTransportBase.cpp
+++ b/quic/api/QuicTransportBase.cpp
@@ -29,7 +29,8 @@ namespace quic {
 
 QuicTransportBase::QuicTransportBase(
     folly::EventBase* evb,
-    std::unique_ptr<folly::AsyncUDPSocket> socket)
+    std::unique_ptr<folly::AsyncUDPSocket> socket,
+    bool useSplitConnectionCallbacks)
     : evb_(evb),
       socket_(std::move(socket)),
       lossTimeout_(this),
@@ -52,7 +53,8 @@ QuicTransportBase::QuicTransportBase(
       writeLooper_(new FunctionLooper(
           evb,
           [this](bool fromTimer) { pacedWriteDataToSocket(fromTimer); },
-          LooperType::WriteLooper)) {
+          LooperType::WriteLooper)),
+      useSplitConnectionCallbacks_(useSplitConnectionCallbacks) {
   writeLooper_->setPacingFunction([this]() -> auto {
     if (isConnectionPaced(*conn_)) {
       return conn_->pacer->getTimeUntilNextWrite();
diff --git a/quic/api/QuicTransportBase.h b/quic/api/QuicTransportBase.h
index 5e93c3eab..a3a137710 100644
--- a/quic/api/QuicTransportBase.h
+++ b/quic/api/QuicTransportBase.h
@@ -39,7 +39,8 @@ class QuicTransportBase : public QuicSocket {
  public:
   QuicTransportBase(
       folly::EventBase* evb,
-      std::unique_ptr<folly::AsyncUDPSocket> socket);
+      std::unique_ptr<folly::AsyncUDPSocket> socket,
+      bool useSplitConnectionCallbacks = false);
 
   ~QuicTransportBase() override;
 
@@ -875,6 +876,11 @@ class QuicTransportBase : public QuicSocket {
   std::shared_ptr<ObserverVec> observers_{std::make_shared<ObserverVec>()};
 
   uint64_t qlogRefcnt_{0};
+
+  // Temp flag controlling which connection callbacks to use - old single
+  // callback object or two new split callback objects. Will be removed out once
+  // mvfst is switched to the new split callbacks eventually.
+  bool useSplitConnectionCallbacks_{false};
 };
 
 std::ostream& operator<<(std::ostream& os, const QuicTransportBase& qt);
diff --git a/quic/client/QuicClientTransport.cpp b/quic/client/QuicClientTransport.cpp
index ac0ce3387..393700988 100644
--- a/quic/client/QuicClientTransport.cpp
+++ b/quic/client/QuicClientTransport.cpp
@@ -39,12 +39,14 @@ QuicClientTransport::QuicClientTransport(
     std::unique_ptr<folly::AsyncUDPSocket> socket,
     std::shared_ptr<ClientHandshakeFactory> handshakeFactory,
     size_t connectionIdSize,
-    PacketNum startingPacketNum)
+    PacketNum startingPacketNum,
+    bool useSplitConnectionCallbacks)
     : QuicClientTransport(
           evb,
           std::move(socket),
           std::move(handshakeFactory),
-          connectionIdSize) {
+          connectionIdSize,
+          useSplitConnectionCallbacks) {
   conn_->ackStates = AckStates(startingPacketNum);
 }
 
@@ -52,8 +54,9 @@ QuicClientTransport::QuicClientTransport(
     folly::EventBase* evb,
     std::unique_ptr<folly::AsyncUDPSocket> socket,
     std::shared_ptr<ClientHandshakeFactory> handshakeFactory,
-    size_t connectionIdSize)
-    : QuicTransportBase(evb, std::move(socket)),
+    size_t connectionIdSize,
+    bool useSplitConnectionCallbacks)
+    : QuicTransportBase(evb, std::move(socket), useSplitConnectionCallbacks),
       happyEyeballsConnAttemptDelayTimeout_(this) {
   DCHECK(handshakeFactory);
   auto tempConn =
diff --git a/quic/client/QuicClientTransport.h b/quic/client/QuicClientTransport.h
index 6b6259f36..4c0ad1ae9 100644
--- a/quic/client/QuicClientTransport.h
+++ b/quic/client/QuicClientTransport.h
@@ -32,7 +32,8 @@ class QuicClientTransport
       folly::EventBase* evb,
       std::unique_ptr<folly::AsyncUDPSocket> socket,
       std::shared_ptr<ClientHandshakeFactory> handshakeFactory,
-      size_t connectionIdSize = 0);
+      size_t connectionIdSize = 0,
+      bool useSplitConnectionCallbacks = false);
 
   // Testing only API:
   QuicClientTransport(
@@ -40,7 +41,8 @@ class QuicClientTransport
       std::unique_ptr<folly::AsyncUDPSocket> socket,
       std::shared_ptr<ClientHandshakeFactory> handshakeFactory,
       size_t connectionIdSize,
-      PacketNum startingPacketNum);
+      PacketNum startingPacketNum,
+      bool useSplitConnectionCallbacks = false);
 
   ~QuicClientTransport() override;
 
@@ -59,9 +61,14 @@ class QuicClientTransport
       folly::EventBase* evb,
       std::unique_ptr<folly::AsyncUDPSocket> sock,
       std::shared_ptr<ClientHandshakeFactory> handshakeFactory,
-      size_t connectionIdSize = 0) {
+      size_t connectionIdSize = 0,
+      bool useSplitConnectionCallbacks = false) {
     auto client = std::make_shared<TransportType>(
-        evb, std::move(sock), std::move(handshakeFactory), connectionIdSize);
+        evb,
+        std::move(sock),
+        std::move(handshakeFactory),
+        connectionIdSize,
+        useSplitConnectionCallbacks);
     client->setSelfOwning();
     return client;
   }
diff --git a/quic/fizz/client/test/QuicClientTransportTest.cpp b/quic/fizz/client/test/QuicClientTransportTest.cpp
index da63b306d..8dafc6724 100644
--- a/quic/fizz/client/test/QuicClientTransportTest.cpp
+++ b/quic/fizz/client/test/QuicClientTransportTest.cpp
@@ -85,12 +85,14 @@ class TestingQuicClientTransport : public QuicClientTransport {
       folly::EventBase* evb,
       std::unique_ptr<folly::AsyncUDPSocket> socket,
       std::shared_ptr<ClientHandshakeFactory> handshakeFactory,
-      size_t connIdSize = kDefaultConnectionIdSize)
+      size_t connIdSize = kDefaultConnectionIdSize,
+      bool useSplitConnectionCallbacks = false)
       : QuicClientTransport(
             evb,
             std::move(socket),
             std::move(handshakeFactory),
-            connIdSize) {}
+            connIdSize,
+            useSplitConnectionCallbacks) {}
 
   ~TestingQuicClientTransport() override {
     if (destructionCallback_) {
diff --git a/quic/server/QuicServerTransport.cpp b/quic/server/QuicServerTransport.cpp
index 04b0d7e19..4ea8f81d2 100644
--- a/quic/server/QuicServerTransport.cpp
+++ b/quic/server/QuicServerTransport.cpp
@@ -43,7 +43,11 @@ QuicServerTransport::QuicServerTransport(
     ConnectionCallback& cb,
     std::shared_ptr<const fizz::server::FizzServerContext> ctx,
     std::unique_ptr<CryptoFactory> cryptoFactory)
-    : QuicTransportBase(evb, std::move(sock)), ctx_(std::move(ctx)) {
+    : QuicTransportBase(
+          evb,
+          std::move(sock),
+          false /* useSplitConnectionCallbacks */),
+      ctx_(std::move(ctx)) {
   auto tempConn = std::make_unique<QuicServerConnectionState>(
       FizzServerQuicHandshakeContext::Builder()
           .setFizzServerContext(ctx_)