diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index 90a1739..bca806e 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -3935,9 +3935,14 @@
     // If there was a packet write error, write the smallest close possible.
     ScopedPacketFlusher flusher(this);
     // Always bundle an ACK with connection close for debugging purpose.
-    if (error != QUIC_PACKET_WRITE_ERROR &&
-        !uber_received_packet_manager_.IsAckFrameEmpty(
-            QuicUtils::GetPacketNumberSpace(encryption_level_))) {
+    bool send_ack = error != QUIC_PACKET_WRITE_ERROR &&
+                    !uber_received_packet_manager_.IsAckFrameEmpty(
+                        QuicUtils::GetPacketNumberSpace(encryption_level_));
+    if (GetQuicReloadableFlag(quic_single_ack_in_packet)) {
+      QUIC_RELOADABLE_FLAG_COUNT_N(quic_single_ack_in_packet, 1, 2);
+      send_ack = !packet_creator_.has_ack() && send_ack;
+    }
+    if (send_ack) {
       SendAck();
     }
     QuicConnectionCloseFrame* frame;
@@ -3977,9 +3982,14 @@
         use_encryption_level_context_ ? this : nullptr, level);
     // Bundle an ACK of the corresponding packet number space for debugging
     // purpose.
-    if (error != QUIC_PACKET_WRITE_ERROR &&
-        !uber_received_packet_manager_.IsAckFrameEmpty(
-            QuicUtils::GetPacketNumberSpace(encryption_level_))) {
+    bool send_ack = error != QUIC_PACKET_WRITE_ERROR &&
+                    !uber_received_packet_manager_.IsAckFrameEmpty(
+                        QuicUtils::GetPacketNumberSpace(encryption_level_));
+    if (GetQuicReloadableFlag(quic_single_ack_in_packet)) {
+      QUIC_RELOADABLE_FLAG_COUNT_N(quic_single_ack_in_packet, 2, 2);
+      send_ack = !packet_creator_.has_ack() && send_ack;
+    }
+    if (send_ack) {
       QuicFrames frames;
       frames.push_back(GetUpdatedAckFrame());
       packet_creator_.FlushAckFrame(frames);
diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index a329404..2d73601 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc
@@ -12826,6 +12826,32 @@
   EXPECT_FALSE(connection_.IsPathDegrading());
 }
 
+TEST_P(QuicConnectionTest, SingleAckInPacket) {
+  EXPECT_CALL(visitor_, OnSuccessfulVersionNegotiation(_));
+  EXPECT_CALL(visitor_, OnConnectionClosed(_, _));
+  connection_.SetDefaultEncryptionLevel(ENCRYPTION_FORWARD_SECURE);
+  connection_.RemoveEncrypter(ENCRYPTION_INITIAL);
+  connection_.NeuterUnencryptedPackets();
+  connection_.OnHandshakeComplete();
+
+  EXPECT_CALL(visitor_, OnStreamFrame(_)).WillOnce(Invoke([=]() {
+    connection_.SendStreamData3();
+    connection_.CloseConnection(
+        QUIC_INTERNAL_ERROR, "error",
+        ConnectionCloseBehavior::SEND_CONNECTION_CLOSE_PACKET);
+  }));
+  QuicFrames frames;
+  frames.push_back(QuicFrame(frame1_));
+  ProcessFramesPacketWithAddresses(frames, kSelfAddress, kPeerAddress,
+                                   ENCRYPTION_FORWARD_SECURE);
+  ASSERT_FALSE(writer_->ack_frames().empty());
+  if (GetQuicReloadableFlag(quic_single_ack_in_packet)) {
+    EXPECT_EQ(1u, writer_->ack_frames().size());
+  } else {
+    EXPECT_EQ(2u, writer_->ack_frames().size());
+  }
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace quic
diff --git a/quic/core/quic_flags_list.h b/quic/core/quic_flags_list.h
index 473106f..3327c5f 100644
--- a/quic/core/quic_flags_list.h
+++ b/quic/core/quic_flags_list.h
@@ -68,6 +68,7 @@
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_send_path_response, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_send_timestamps, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_send_version_negotiation_for_short_connection_ids, true)
+QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_single_ack_in_packet, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_split_up_send_rst_2, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_start_peer_migration_earlier, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_stop_sending_uses_ietf_error_code, true)
diff --git a/quic/core/quic_packet_creator.cc b/quic/core/quic_packet_creator.cc
index 087b427..e1e3478 100644
--- a/quic/core/quic_packet_creator.cc
+++ b/quic/core/quic_packet_creator.cc
@@ -1426,6 +1426,8 @@
 bool QuicPacketCreator::FlushAckFrame(const QuicFrames& frames) {
   QUIC_BUG_IF(!flusher_attached_) << "Packet flusher is not attached when "
                                      "generator tries to send ACK frame.";
+  QUIC_BUG_IF(GetQuicReloadableFlag(quic_single_ack_in_packet) && has_ack())
+      << "Trying to flush " << frames << " when there is ACK queued";
   for (const auto& frame : frames) {
     DCHECK(frame.type == ACK_FRAME || frame.type == STOP_WAITING_FRAME);
     if (HasPendingFrames()) {