diff --git a/quiche/common/quiche_feature_flags_list.h b/quiche/common/quiche_feature_flags_list.h
index fd35cc9..f106854 100755
--- a/quiche/common/quiche_feature_flags_list.h
+++ b/quiche/common/quiche_feature_flags_list.h
@@ -48,7 +48,7 @@
 QUICHE_FLAG(bool, quiche_reloadable_flag_quic_testonly_default_false, false, "A testonly reloadable flag that will always default to false.")
 QUICHE_FLAG(bool, quiche_reloadable_flag_quic_testonly_default_true, true, "A testonly reloadable flag that will always default to true.")
 QUICHE_FLAG(bool, quiche_reloadable_flag_quic_use_received_client_addresses_cache, true, "If true, use a LRU cache to record client addresses of packets received on server's original address.")
-QUICHE_FLAG(bool, quiche_restart_flag_quic_opport_bundle_qpack_decoder_data3, false, "If true, always bundle qpack decoder data with other frames opportunistically.")
+QUICHE_FLAG(bool, quiche_restart_flag_quic_opport_bundle_qpack_decoder_data4, false, "If true, bundle qpack decoder data with other frames opportunistically.")
 QUICHE_FLAG(bool, quiche_restart_flag_quic_support_ect1, false, "When true, allows sending of QUIC packets marked ECT(1). A different flag (TBD) will actually utilize this capability to send ECT(1).")
 QUICHE_FLAG(bool, quiche_restart_flag_quic_support_release_time_for_gso, false, "If true, QuicGsoBatchWriter will support release time if it is available and the process has the permission to do so.")
 QUICHE_FLAG(bool, quiche_restart_flag_quic_testonly_default_false, false, "A testonly restart flag that will always default to false.")
diff --git a/quiche/quic/core/http/end_to_end_test.cc b/quiche/quic/core/http/end_to_end_test.cc
index e354a7f..249bc93 100644
--- a/quiche/quic/core/http/end_to_end_test.cc
+++ b/quiche/quic/core/http/end_to_end_test.cc
@@ -2847,7 +2847,7 @@
       client_connection->GetStats().packets_sent;
 
   if (version_.UsesHttp3()) {
-    if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+    if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
       // QPACK decoder instructions and RESET_STREAM and STOP_SENDING frames are
       // sent in a single packet.
       EXPECT_EQ(packets_sent_before + 1, packets_sent_now);
@@ -3030,7 +3030,7 @@
     return;
   }
   override_client_connection_id_length_ = kQuicDefaultConnectionIdLength;
-  SetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3, false);
+  SetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4, false);
   ASSERT_TRUE(Initialize());
   SendSynchronousFooRequestAndCheckResponse();
 
diff --git a/quiche/quic/core/http/quic_spdy_session.cc b/quiche/quic/core/http/quic_spdy_session.cc
index df57d20..752f83f 100644
--- a/quiche/quic/core/http/quic_spdy_session.cc
+++ b/quiche/quic/core/http/quic_spdy_session.cc
@@ -866,7 +866,7 @@
 }
 
 bool QuicSpdySession::CheckStreamWriteBlocked(QuicStream* stream) const {
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3) &&
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4) &&
       qpack_decoder_send_stream_ != nullptr &&
       stream->id() == qpack_decoder_send_stream_->id()) {
     // Decoder data is always bundled opportunistically.
diff --git a/quiche/quic/core/http/quic_spdy_session_test.cc b/quiche/quic/core/http/quic_spdy_session_test.cc
index 2dace2d..fc9ed5c 100644
--- a/quiche/quic/core/http/quic_spdy_session_test.cc
+++ b/quiche/quic/core/http/quic_spdy_session_test.cc
@@ -1361,7 +1361,7 @@
   // In HTTP/3, Qpack stream will send data on stream reset and cause packet to
   // be flushed.
   if (VersionUsesHttp3(transport_version()) &&
-      !GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+      !GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(*writer_, WritePacket(_, _, _, _, _, _))
         .WillOnce(Return(WriteResult(WRITE_STATUS_OK, 0)));
   }
@@ -1606,7 +1606,7 @@
     // the STOP_SENDING, so set up the EXPECT there.
     EXPECT_CALL(*connection_, OnStreamReset(stream->id(), _));
     EXPECT_CALL(*connection_, SendControlFrame(_));
-  } else if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  } else if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(*writer_, WritePacket(_, _, _, _, _, _))
         .WillOnce(Return(WriteResult(WRITE_STATUS_OK, 0)));
   }
diff --git a/quiche/quic/core/http/quic_spdy_stream_test.cc b/quiche/quic/core/http/quic_spdy_stream_test.cc
index d693c9f..0848648 100644
--- a/quiche/quic/core/http/quic_spdy_stream_test.cc
+++ b/quiche/quic/core/http/quic_spdy_stream_test.cc
@@ -584,7 +584,7 @@
           stream_->id(),
           QuicResetStreamError::FromInternal(QUIC_HEADERS_TOO_LARGE), 0));
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     auto qpack_decoder_stream =
         QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
     // Stream type and stream cancellation.
@@ -2256,7 +2256,7 @@
   std::string headers = HeadersFrame(encoded_headers);
   EXPECT_CALL(debug_visitor,
               OnHeadersFrameReceived(stream_->id(), encoded_headers.length()));
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Decoder stream type.
     EXPECT_CALL(*session_,
                 WritevData(decoder_send_stream->id(), /* write_length = */ 1,
@@ -2294,7 +2294,7 @@
   EXPECT_CALL(debug_visitor,
               OnHeadersFrameReceived(stream_->id(), encoded_trailers.length()));
   // Header acknowledgement.
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(*session_,
                 WritevData(decoder_send_stream->id(), _, _, _, _, _));
   }
@@ -2337,7 +2337,7 @@
   auto decoder_send_stream =
       QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Decoder stream type.
     EXPECT_CALL(*session_,
                 WritevData(decoder_send_stream->id(), /* write_length = */ 1,
@@ -2377,7 +2377,7 @@
   // Decoding is blocked because dynamic table entry has not been received yet.
   EXPECT_FALSE(stream_->trailers_decompressed());
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Header acknowledgement.
     EXPECT_CALL(*session_,
                 WritevData(decoder_send_stream->id(), _, _, _, _, _));
@@ -2478,7 +2478,7 @@
   auto decoder_send_stream =
       QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Decoder stream type.
     EXPECT_CALL(*session_,
                 WritevData(decoder_send_stream->id(), /* write_length = */ 1,
@@ -2552,7 +2552,7 @@
   // Decoding is blocked because dynamic table entry has not been received yet.
   EXPECT_FALSE(stream_->headers_decompressed());
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Decoder stream type and stream cancellation instruction.
     auto decoder_send_stream =
         QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
@@ -2603,7 +2603,7 @@
   // Decoding is blocked because dynamic table entry has not been received yet.
   EXPECT_FALSE(stream_->headers_decompressed());
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Decoder stream type and stream cancellation instruction.
     auto decoder_send_stream =
         QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
@@ -3117,7 +3117,7 @@
 
   auto qpack_decoder_stream =
       QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Stream type.
     EXPECT_CALL(*session_,
                 WritevData(qpack_decoder_stream->id(), /* write_length = */ 1,
@@ -3150,7 +3150,7 @@
 
   auto qpack_decoder_stream =
       QuicSpdySessionPeer::GetQpackDecoderSendStream(session_.get());
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // Stream type.
     EXPECT_CALL(*session_,
                 WritevData(qpack_decoder_stream->id(), /* write_length = */ 1,
@@ -3544,7 +3544,7 @@
   QuicStreamFrame frame(stream_->id(), /* fin = */ false, 0, data_frame);
   stream_->OnStreamFrame(frame);
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     // As a result of resetting the stream, stream type and stream cancellation
     // are sent on the QPACK decoder stream.
     auto qpack_decoder_stream =
diff --git a/quiche/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc b/quiche/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc
index 3b64e99..1a718a5 100644
--- a/quiche/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc
+++ b/quiche/quic/core/qpack/qpack_decoded_headers_accumulator_test.cc
@@ -191,7 +191,7 @@
 
   EXPECT_CALL(visitor_, OnHeadersDecoded(_, true));
   qpack_decoder_.OnInsertWithoutNameReference("foo", "bar");
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     qpack_decoder_.FlushDecoderStream();
   }
 }
@@ -218,7 +218,7 @@
   EXPECT_EQ(strlen("foo") + strlen("bar"),
             header_list.uncompressed_header_bytes());
   EXPECT_EQ(encoded_data.size(), header_list.compressed_header_bytes());
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     qpack_decoder_.FlushDecoderStream();
   }
 }
@@ -247,7 +247,7 @@
   accumulator_.EndHeaderBlock();
 
   EXPECT_THAT(header_list, ElementsAre(Pair("foo", "bar"), Pair("foo", "bar")));
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     qpack_decoder_.FlushDecoderStream();
   }
 }
diff --git a/quiche/quic/core/qpack/qpack_decoder.cc b/quiche/quic/core/qpack/qpack_decoder.cc
index a0ce09b..02c590d 100644
--- a/quiche/quic/core/qpack/qpack_decoder.cc
+++ b/quiche/quic/core/qpack/qpack_decoder.cc
@@ -31,7 +31,7 @@
 void QpackDecoder::OnStreamReset(QuicStreamId stream_id) {
   if (header_table_.maximum_dynamic_table_capacity() > 0) {
     decoder_stream_sender_.SendStreamCancellation(stream_id);
-    if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+    if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
       decoder_stream_sender_.Flush();
     }
   }
@@ -68,7 +68,7 @@
     known_received_count_ = header_table_.inserted_entry_count();
   }
 
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     decoder_stream_sender_.Flush();
   }
 }
diff --git a/quiche/quic/core/qpack/qpack_decoder_stream_sender.cc b/quiche/quic/core/qpack/qpack_decoder_stream_sender.cc
index da33bd3..98245c4 100644
--- a/quiche/quic/core/qpack/qpack_decoder_stream_sender.cc
+++ b/quiche/quic/core/qpack/qpack_decoder_stream_sender.cc
@@ -42,8 +42,8 @@
   if (buffer_.empty() || delegate_ == nullptr) {
     return;
   }
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
-    QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data3, 3, 4);
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
+    QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data4, 3, 4);
     // Swap buffer_ before calling WriteStreamData, which might result in a
     // reentrant call to `Flush()`.
     std::string copy;
diff --git a/quiche/quic/core/qpack/qpack_decoder_test.cc b/quiche/quic/core/qpack/qpack_decoder_test.cc
index ce37190..78fadd2 100644
--- a/quiche/quic/core/qpack/qpack_decoder_test.cc
+++ b/quiche/quic/core/qpack/qpack_decoder_test.cc
@@ -420,13 +420,13 @@
       .InSequence(s);
   EXPECT_CALL(handler_, OnHeaderDecoded(Eq("foo"), Eq("ZZZ"))).InSequence(s);
   EXPECT_CALL(handler_, OnHeaderDecoded(Eq(":method"), Eq("ZZ"))).InSequence(s);
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(decoder_stream_sender_delegate_,
                 WriteStreamData(Eq(kHeaderAcknowledgement)))
         .InSequence(s);
   }
   EXPECT_CALL(handler_, OnDecodingCompleted()).InSequence(s);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(decoder_stream_sender_delegate_,
                 WriteStreamData(Eq(kHeaderAcknowledgement)))
         .InSequence(s);
@@ -443,7 +443,7 @@
                    // with value "ZZ".
       &input));
   DecodeHeaderBlock(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 
@@ -453,13 +453,13 @@
       .InSequence(s);
   EXPECT_CALL(handler_, OnHeaderDecoded(Eq("foo"), Eq("ZZZ"))).InSequence(s);
   EXPECT_CALL(handler_, OnHeaderDecoded(Eq(":method"), Eq("ZZ"))).InSequence(s);
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(decoder_stream_sender_delegate_,
                 WriteStreamData(Eq(kHeaderAcknowledgement)))
         .InSequence(s);
   }
   EXPECT_CALL(handler_, OnDecodingCompleted()).InSequence(s);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(decoder_stream_sender_delegate_,
                 WriteStreamData(Eq(kHeaderAcknowledgement)))
         .InSequence(s);
@@ -476,7 +476,7 @@
                    // with value "ZZ".
       &input));
   DecodeHeaderBlock(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 
@@ -486,13 +486,13 @@
       .InSequence(s);
   EXPECT_CALL(handler_, OnHeaderDecoded(Eq("foo"), Eq("ZZZ"))).InSequence(s);
   EXPECT_CALL(handler_, OnHeaderDecoded(Eq(":method"), Eq("ZZ"))).InSequence(s);
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(decoder_stream_sender_delegate_,
                 WriteStreamData(Eq(kHeaderAcknowledgement)))
         .InSequence(s);
   }
   EXPECT_CALL(handler_, OnDecodingCompleted()).InSequence(s);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(decoder_stream_sender_delegate_,
                 WriteStreamData(Eq(kHeaderAcknowledgement)))
         .InSequence(s);
@@ -509,7 +509,7 @@
                    // with value "ZZ".
       &input));
   DecodeHeaderBlock(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
@@ -550,7 +550,7 @@
       "80",   // Dynamic table entry with relative index 0, absolute index 0.
       &input));
   DecodeHeaderBlock(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
@@ -837,7 +837,7 @@
       "80",   // Emit dynamic table entry with relative index 0.
       &input));
   DecodeHeaderBlock(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
@@ -1032,7 +1032,7 @@
   // Add literal entry with name "foo" and value "bar".
   ASSERT_TRUE(absl::HexStringToBytes("6294e703626172", &input));
   DecodeEncoderStreamData(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
@@ -1079,7 +1079,7 @@
   EXPECT_CALL(decoder_stream_sender_delegate_,
               WriteStreamData(Eq(kHeaderAcknowledgement)));
   EndDecoding();
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
@@ -1147,7 +1147,7 @@
   // Insert Count is now 6, reaching Required Insert Count of the header block.
   ASSERT_TRUE(absl::HexStringToBytes("6294e70362617a", &input));
   DecodeEncoderStreamData(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
@@ -1199,7 +1199,7 @@
       "80",   // Dynamic table entry with relative index 0, absolute index 0.
       &input));
   DecodeHeaderBlock(input);
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     FlushDecoderStream();
   }
 }
diff --git a/quiche/quic/core/quic_connection.cc b/quiche/quic/core/quic_connection.cc
index 6a1e0a8..e5fcc38 100644
--- a/quiche/quic/core/quic_connection.cc
+++ b/quiche/quic/core/quic_connection.cc
@@ -3177,20 +3177,37 @@
   return connected_ && !HandleWriteBlocked();
 }
 
-void QuicConnection::MaybeBundleOpportunistically() {
-  if (!ack_frequency_sent_ && sent_packet_manager_.CanSendAckFrequency()) {
-    if (packet_creator_.NextSendingPacketNumber() >=
-        FirstSendingPacketNumber() + kMinReceivedBeforeAckDecimation) {
+void QuicConnection::MaybeBundleOpportunistically(
+    TransmissionType transmission_type) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
+    QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data4, 1, 4);
+
+    const bool should_bundle_ack_frequency =
+        !ack_frequency_sent_ && sent_packet_manager_.CanSendAckFrequency() &&
+        transmission_type == NOT_RETRANSMISSION &&
+        packet_creator_.NextSendingPacketNumber() >=
+            FirstSendingPacketNumber() + kMinReceivedBeforeAckDecimation;
+
+    if (should_bundle_ack_frequency) {
       QUIC_RELOADABLE_FLAG_COUNT_N(quic_can_send_ack_frequency, 3, 3);
       ack_frequency_sent_ = true;
       auto frame = sent_packet_manager_.GetUpdatedAckFrequencyFrame();
       visitor_->SendAckFrequency(frame);
     }
-  }
 
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
-    QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data3, 1, 4);
-    visitor_->MaybeBundleOpportunistically();
+    if (transmission_type == NOT_RETRANSMISSION) {
+      visitor_->MaybeBundleOpportunistically();
+    }
+  } else {
+    if (!ack_frequency_sent_ && sent_packet_manager_.CanSendAckFrequency()) {
+      if (packet_creator_.NextSendingPacketNumber() >=
+          FirstSendingPacketNumber() + kMinReceivedBeforeAckDecimation) {
+        QUIC_RELOADABLE_FLAG_COUNT_N(quic_can_send_ack_frequency, 3, 3);
+        ack_frequency_sent_ = true;
+        auto frame = sent_packet_manager_.GetUpdatedAckFrequencyFrame();
+        visitor_->SendAckFrequency(frame);
+      }
+    }
   }
 
   if (packet_creator_.has_ack() || !CanWrite(NO_RETRANSMITTABLE_DATA)) {
@@ -5817,8 +5834,8 @@
       uber_received_packet_manager_.GetEarliestAckTimeout();
   QUIC_BUG_IF(quic_bug_12714_32, !earliest_ack_timeout.IsInitialized());
   MaybeBundleCryptoDataWithAcks();
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
-    QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data3, 2, 4);
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
+    QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data4, 2, 4);
     visitor_->MaybeBundleOpportunistically();
   }
   earliest_ack_timeout = uber_received_packet_manager_.GetEarliestAckTimeout();
diff --git a/quiche/quic/core/quic_connection.h b/quiche/quic/core/quic_connection.h
index 0113dde..36f0aca 100644
--- a/quiche/quic/core/quic_connection.h
+++ b/quiche/quic/core/quic_connection.h
@@ -739,7 +739,8 @@
   // QuicPacketCreator::DelegateInterface
   bool ShouldGeneratePacket(HasRetransmittableData retransmittable,
                             IsHandshake handshake) override;
-  void MaybeBundleOpportunistically() override;
+  void MaybeBundleOpportunistically(
+      TransmissionType transmission_type) override;
   QuicByteCount GetFlowControlSendWindowSize(QuicStreamId id) override {
     return visitor_->GetFlowControlSendWindowSize(id);
   }
diff --git a/quiche/quic/core/quic_connection_test.cc b/quiche/quic/core/quic_connection_test.cc
index 018d5ec..11c98e6 100644
--- a/quiche/quic/core/quic_connection_test.cc
+++ b/quiche/quic/core/quic_connection_test.cc
@@ -700,7 +700,7 @@
     EXPECT_CALL(visitor_, OnCongestionWindowChange(_)).Times(AnyNumber());
     EXPECT_CALL(visitor_, OnPacketReceived(_, _, _)).Times(AnyNumber());
     EXPECT_CALL(visitor_, OnSuccessfulVersionNegotiation(_)).Times(AnyNumber());
-    if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+    if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
       EXPECT_CALL(visitor_, MaybeBundleOpportunistically()).Times(AnyNumber());
       EXPECT_CALL(visitor_, GetFlowControlSendWindowSize(_)).Times(AnyNumber());
     }
diff --git a/quiche/quic/core/quic_dispatcher.cc b/quiche/quic/core/quic_dispatcher.cc
index fc71a6c..1d371e4 100644
--- a/quiche/quic/core/quic_dispatcher.cc
+++ b/quiche/quic/core/quic_dispatcher.cc
@@ -141,7 +141,10 @@
     return true;
   }
 
-  void MaybeBundleOpportunistically() override { QUICHE_DCHECK(false); }
+  void MaybeBundleOpportunistically(
+      TransmissionType /*transmission_type*/) override {
+    QUICHE_DCHECK(false);
+  }
 
   QuicByteCount GetFlowControlSendWindowSize(QuicStreamId /*id*/) override {
     QUICHE_DCHECK(false);
diff --git a/quiche/quic/core/quic_flags_list.h b/quiche/quic/core/quic_flags_list.h
index 90f9a8d..4c7c44c 100644
--- a/quiche/quic/core/quic_flags_list.h
+++ b/quiche/quic/core/quic_flags_list.h
@@ -35,10 +35,10 @@
 QUIC_FLAG(quic_reloadable_flag_quic_allow_client_enabled_bbr_v2, true)
 // If true, allow quic to use new ALPS codepoint to negotiate during handshake for H3 if client sends new ALPS codepoint.
 QUIC_FLAG(quic_reloadable_flag_quic_gfe_allow_alps_new_codepoint, false)
-// If true, always bundle qpack decoder data with other frames opportunistically.
-QUIC_FLAG(quic_restart_flag_quic_opport_bundle_qpack_decoder_data3, false)
 // If true, an endpoint does not detect path degrading or blackholing until handshake gets confirmed.
 QUIC_FLAG(quic_reloadable_flag_quic_no_path_degrading_before_handshake_confirmed, true)
+// If true, bundle qpack decoder data with other frames opportunistically.
+QUIC_FLAG(quic_restart_flag_quic_opport_bundle_qpack_decoder_data4, false)
 // If true, default-enable 5RTO blachole detection.
 QUIC_FLAG(quic_reloadable_flag_quic_default_enable_5rto_blackhole_detection2, true)
 // If true, disable QUIC version Q046.
diff --git a/quiche/quic/core/quic_packet_creator.cc b/quiche/quic/core/quic_packet_creator.cc
index ee22a63..27519df 100644
--- a/quiche/quic/core/quic_packet_creator.cc
+++ b/quiche/quic/core/quic_packet_creator.cc
@@ -1313,15 +1313,15 @@
 }
 
 void QuicPacketCreator::MaybeBundleOpportunistically() {
-  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
-    delegate_->MaybeBundleOpportunistically();
+  if (!GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
+    delegate_->MaybeBundleOpportunistically(next_transmission_type_);
     return;
   }
 
   // delegate_->MaybeBundleOpportunistically() may change
   // next_transmission_type_ for the bundled data.
   const TransmissionType next_transmission_type = next_transmission_type_;
-  delegate_->MaybeBundleOpportunistically();
+  delegate_->MaybeBundleOpportunistically(next_transmission_type_);
   next_transmission_type_ = next_transmission_type;
 }
 
@@ -1337,7 +1337,7 @@
   const TransmissionType next_transmission_type = next_transmission_type_;
   MaybeBundleOpportunistically();
   // TODO(wub): Remove this QUIC_BUG when deprecating
-  // quic_opport_bundle_qpack_decoder_data3.
+  // quic_opport_bundle_qpack_decoder_data4.
   QUIC_BUG_IF(quic_packet_creator_change_transmission_type,
               next_transmission_type != next_transmission_type_)
       << ENDPOINT
@@ -1352,11 +1352,11 @@
   // - It is not a retransmission. We check next_transmission_type_ for that.
   // - And it's not handshake data. This is always true for ConsumeData because
   //   the function is not called for handshake data.
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3) &&
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4) &&
       next_transmission_type_ == NOT_RETRANSMISSION) {
     if (QuicByteCount send_window = delegate_->GetFlowControlSendWindowSize(id);
         write_length > send_window) {
-      QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data3, 4, 4);
+      QUIC_RESTART_FLAG_COUNT_N(quic_opport_bundle_qpack_decoder_data4, 4, 4);
       QUIC_DLOG(INFO) << ENDPOINT
                       << "After bundled data, reducing (old) write_length:"
                       << write_length << "to (new) send_window:" << send_window;
diff --git a/quiche/quic/core/quic_packet_creator.h b/quiche/quic/core/quic_packet_creator.h
index e624dc1..6c3fc73 100644
--- a/quiche/quic/core/quic_packet_creator.h
+++ b/quiche/quic/core/quic_packet_creator.h
@@ -61,8 +61,10 @@
     virtual bool ShouldGeneratePacket(HasRetransmittableData retransmittable,
                                       IsHandshake handshake) = 0;
     // Called when there is data to be sent. Gives delegate a chance to bundle
-    // anything with to-be-sent data.
-    virtual void MaybeBundleOpportunistically() = 0;
+    // anything with to-be-sent data. |transmission_type| is the transmission
+    // type of the data being sent.
+    virtual void MaybeBundleOpportunistically(
+        TransmissionType transmission_type) = 0;
 
     // When sending flow controlled data, this will be called after
     // MaybeBundleOpportunistically(). If the returned flow control send window
diff --git a/quiche/quic/core/quic_packet_creator_test.cc b/quiche/quic/core/quic_packet_creator_test.cc
index 2b67c0b..472dc7f 100644
--- a/quiche/quic/core/quic_packet_creator_test.cc
+++ b/quiche/quic/core/quic_packet_creator_test.cc
@@ -2540,7 +2540,8 @@
   MOCK_METHOD(bool, ShouldGeneratePacket,
               (HasRetransmittableData retransmittable, IsHandshake handshake),
               (override));
-  MOCK_METHOD(void, MaybeBundleOpportunistically, (), (override));
+  MOCK_METHOD(void, MaybeBundleOpportunistically,
+              (TransmissionType transmission_type), (override));
   MOCK_METHOD(QuicByteCount, GetFlowControlSendWindowSize, (QuicStreamId),
               (override));
   MOCK_METHOD(QuicPacketBuffer, GetPacketBuffer, (), (override));
@@ -2618,7 +2619,7 @@
     if (bundle_ack) {
       frames.push_back(QuicFrame(&ack_frame_));
     }
-    EXPECT_CALL(*delegate_, MaybeBundleOpportunistically())
+    EXPECT_CALL(*delegate_, MaybeBundleOpportunistically(_))
         .WillOnce(Invoke([this, frames = std::move(frames)] {
           FlushAckFrame(frames);
           return QuicFrames();
@@ -2644,7 +2645,7 @@
     if (!data.empty()) {
       producer_->SaveStreamData(id, data);
     }
-    EXPECT_CALL(*delegate_, MaybeBundleOpportunistically()).Times(1);
+    EXPECT_CALL(*delegate_, MaybeBundleOpportunistically(_)).Times(1);
     return QuicPacketCreator::ConsumeData(id, data.length(), offset, state);
   }
 
@@ -2652,7 +2653,7 @@
                                 quiche::QuicheMemSlice message) {
     if (!has_ack() && delegate_->ShouldGeneratePacket(NO_RETRANSMITTABLE_DATA,
                                                       NOT_HANDSHAKE)) {
-      EXPECT_CALL(*delegate_, MaybeBundleOpportunistically()).Times(1);
+      EXPECT_CALL(*delegate_, MaybeBundleOpportunistically(_)).Times(1);
     }
     return QuicPacketCreator::AddMessageFrame(message_id,
                                               absl::MakeSpan(&message, 1));
@@ -2661,7 +2662,7 @@
   size_t ConsumeCryptoData(EncryptionLevel level, absl::string_view data,
                            QuicStreamOffset offset) {
     producer_->SaveCryptoData(level, offset, data);
-    EXPECT_CALL(*delegate_, MaybeBundleOpportunistically()).Times(1);
+    EXPECT_CALL(*delegate_, MaybeBundleOpportunistically(_)).Times(1);
     return QuicPacketCreator::ConsumeCryptoData(level, data.length(), offset);
   }
 
@@ -2930,7 +2931,7 @@
   QuicStreamId stream_id = QuicUtils::GetFirstBidirectionalStreamId(
       framer_.transport_version(), Perspective::IS_CLIENT);
 
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(delegate_, GetFlowControlSendWindowSize(stream_id))
         .WillOnce(Return(data.length() - 1));
   } else {
@@ -2939,7 +2940,7 @@
 
   QuicConsumedData consumed = creator_.ConsumeData(stream_id, data, 0u, FIN);
 
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_EQ(consumed.bytes_consumed, data.length() - 1);
     EXPECT_FALSE(consumed.fin_consumed);
   } else {
@@ -2960,7 +2961,7 @@
   QuicStreamId stream_id = QuicUtils::GetFirstBidirectionalStreamId(
       framer_.transport_version(), Perspective::IS_CLIENT);
 
-  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data3)) {
+  if (GetQuicRestartFlag(quic_opport_bundle_qpack_decoder_data4)) {
     EXPECT_CALL(delegate_, GetFlowControlSendWindowSize(stream_id))
         .WillOnce(Return(data.length()));
   } else {
diff --git a/quiche/quic/test_tools/quic_test_utils.h b/quiche/quic/test_tools/quic_test_utils.h
index 72f5bd0..047fdbe 100644
--- a/quiche/quic/test_tools/quic_test_utils.h
+++ b/quiche/quic/test_tools/quic_test_utils.h
@@ -1415,7 +1415,8 @@
   MOCK_METHOD(bool, ShouldGeneratePacket,
               (HasRetransmittableData retransmittable, IsHandshake handshake),
               (override));
-  MOCK_METHOD(void, MaybeBundleOpportunistically, (), (override));
+  MOCK_METHOD(void, MaybeBundleOpportunistically,
+              (TransmissionType transmission_type), (override));
   MOCK_METHOD(QuicByteCount, GetFlowControlSendWindowSize, (QuicStreamId),
               (override));
   MOCK_METHOD(SerializedPacketFate, GetSerializedPacketFate,