diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index 060a971..bf61ade 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc
@@ -6220,6 +6220,9 @@
 }
 
 TEST_P(QuicConnectionTest, SendDelayedAfterQuiescence) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   QuicConnectionPeer::SetFastAckAfterQuiescence(&connection_, true);
 
   // The beginning of the connection counts as quiescence.
@@ -6352,6 +6355,9 @@
 }
 
 TEST_P(QuicConnectionTest, SendDelayedAckAckDecimationAfterQuiescence) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_CALL(visitor_, OnAckNeedsRetransmittableFrame()).Times(AnyNumber());
   QuicConnectionPeer::SetAckMode(&connection_, ACK_DECIMATION);
   QuicConnectionPeer::SetFastAckAfterQuiescence(&connection_, true);
@@ -6603,6 +6609,9 @@
 }
 
 TEST_P(QuicConnectionTest, SendDelayedAckDecimationWithReordering) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_CALL(visitor_, OnAckNeedsRetransmittableFrame()).Times(AnyNumber());
   QuicConnectionPeer::SetAckMode(&connection_, ACK_DECIMATION_WITH_REORDERING);
 
@@ -6668,6 +6677,9 @@
 }
 
 TEST_P(QuicConnectionTest, SendDelayedAckDecimationWithLargeReordering) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_CALL(visitor_, OnAckNeedsRetransmittableFrame()).Times(AnyNumber());
   QuicConnectionPeer::SetAckMode(&connection_, ACK_DECIMATION_WITH_REORDERING);
 
@@ -6751,6 +6763,9 @@
 }
 
 TEST_P(QuicConnectionTest, SendDelayedAckDecimationWithReorderingEighthRtt) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_CALL(visitor_, OnAckNeedsRetransmittableFrame()).Times(AnyNumber());
   QuicConnectionPeer::SetAckMode(&connection_, ACK_DECIMATION_WITH_REORDERING);
   QuicConnectionPeer::SetAckDecimationDelay(&connection_, 0.125);
@@ -6820,6 +6835,9 @@
 
 TEST_P(QuicConnectionTest,
        SendDelayedAckDecimationWithLargeReorderingEighthRtt) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_CALL(visitor_, OnAckNeedsRetransmittableFrame()).Times(AnyNumber());
   QuicConnectionPeer::SetAckMode(&connection_, ACK_DECIMATION_WITH_REORDERING);
   QuicConnectionPeer::SetAckDecimationDelay(&connection_, 0.125);
diff --git a/quic/core/quic_received_packet_manager.cc b/quic/core/quic_received_packet_manager.cc
index 942c8b5..324767c 100644
--- a/quic/core/quic_received_packet_manager.cc
+++ b/quic/core/quic_received_packet_manager.cc
@@ -60,28 +60,39 @@
 
 void QuicReceivedPacketManager::SetFromConfig(const QuicConfig& config,
                                               Perspective perspective) {
-  if (config.HasClientSentConnectionOption(kACD0, perspective)) {
-    ack_mode_ = TCP_ACKING;
+  if (remove_unused_ack_options_) {
+    QUIC_RELOADABLE_FLAG_COUNT(quic_remove_unused_ack_options);
   }
-  if (config.HasClientSentConnectionOption(kACKD, perspective)) {
-    ack_mode_ = ACK_DECIMATION;
-  }
-  if (config.HasClientSentConnectionOption(kAKD2, perspective)) {
-    ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
+  if (!remove_unused_ack_options_) {
+    if (config.HasClientSentConnectionOption(kACD0, perspective)) {
+      ack_mode_ = TCP_ACKING;
+    }
+    if (config.HasClientSentConnectionOption(kACKD, perspective)) {
+      ack_mode_ = ACK_DECIMATION;
+    }
+    if (config.HasClientSentConnectionOption(kAKD2, perspective)) {
+      ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
+    }
   }
   if (config.HasClientSentConnectionOption(kAKD3, perspective)) {
-    ack_mode_ = ACK_DECIMATION;
+    if (!remove_unused_ack_options_) {
+      ack_mode_ = ACK_DECIMATION;
+    }
     ack_decimation_delay_ = kShortAckDecimationDelay;
   }
-  if (config.HasClientSentConnectionOption(kAKD4, perspective)) {
-    ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
-    ack_decimation_delay_ = kShortAckDecimationDelay;
+  if (!remove_unused_ack_options_) {
+    if (config.HasClientSentConnectionOption(kAKD4, perspective)) {
+      ack_mode_ = ACK_DECIMATION_WITH_REORDERING;
+      ack_decimation_delay_ = kShortAckDecimationDelay;
+    }
   }
   if (config.HasClientSentConnectionOption(kAKDU, perspective)) {
     unlimited_ack_decimation_ = true;
   }
-  if (config.HasClientSentConnectionOption(kACKQ, perspective)) {
-    fast_ack_after_quiescence_ = true;
+  if (!remove_unused_ack_options_) {
+    if (config.HasClientSentConnectionOption(kACKQ, perspective)) {
+      fast_ack_after_quiescence_ = true;
+    }
   }
   if (config.HasClientSentConnectionOption(k1ACK, perspective)) {
     one_immediate_ack_ = true;
@@ -274,7 +285,10 @@
 
   // If there are new missing packets to report, send an ack immediately.
   if (HasNewMissingPackets()) {
+    // TODO(haoyuewang) Remove ACK_DECIMATION_WITH_REORDERING after
+    // quic_remove_unused_ack_options is deprecated.
     if (ack_mode_ == ACK_DECIMATION_WITH_REORDERING) {
+      DCHECK(!remove_unused_ack_options_);
       // Wait the minimum of an eighth min_rtt and the existing ack time.
       QuicTime ack_time = now + kShortAckDecimationDelay * rtt_stats->min_rtt();
       MaybeUpdateAckTimeoutTo(ack_time);
diff --git a/quic/core/quic_received_packet_manager.h b/quic/core/quic_received_packet_manager.h
index b01390d..a350462 100644
--- a/quic/core/quic_received_packet_manager.h
+++ b/quic/core/quic_received_packet_manager.h
@@ -177,6 +177,8 @@
   bool unlimited_ack_decimation_;
   // When true, use a 1ms delayed ack timer if it's been an SRTT since a packet
   // was received.
+  // TODO(haoyuewang) Remove fast_ack_after_quiescence_ when
+  // quic_remove_unused_ack_options flag is deprecated.
   bool fast_ack_after_quiescence_;
   // When true, only send 1 immediate ACK when reordering is detected.
   bool one_immediate_ack_;
@@ -193,6 +195,11 @@
   // Whether the most recent packet was missing before it was received.
   bool was_last_packet_missing_;
 
+  // TODO(haoyuewang) Remove TCP_ACKING when
+  // fast_ack_after_quiescence_ when this flag is deprecated.
+  const bool remove_unused_ack_options_ =
+      GetQuicReloadableFlag(quic_remove_unused_ack_options);
+
   // Last sent largest acked, which gets updated when ACK was successfully sent.
   QuicPacketNumber last_sent_largest_acked_;
 };
diff --git a/quic/core/quic_received_packet_manager_test.cc b/quic/core/quic_received_packet_manager_test.cc
index bfdf338..56b6643 100644
--- a/quic/core/quic_received_packet_manager_test.cc
+++ b/quic/core/quic_received_packet_manager_test.cc
@@ -402,6 +402,9 @@
 }
 
 TEST_P(QuicReceivedPacketManagerTest, SendDelayedAfterQuiescence) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   QuicReceivedPacketManagerPeer::SetFastAckAfterQuiescence(&received_manager_,
                                                            true);
@@ -505,6 +508,9 @@
 
 TEST_P(QuicReceivedPacketManagerTest,
        SendDelayedAckAckDecimationAfterQuiescence) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   QuicReceivedPacketManagerPeer::SetAckMode(&received_manager_, ACK_DECIMATION);
   QuicReceivedPacketManagerPeer::SetFastAckAfterQuiescence(&received_manager_,
@@ -647,6 +653,9 @@
 }
 
 TEST_P(QuicReceivedPacketManagerTest, SendDelayedAckDecimationWithReordering) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   QuicReceivedPacketManagerPeer::SetAckMode(&received_manager_,
                                             ACK_DECIMATION_WITH_REORDERING);
@@ -690,6 +699,9 @@
 
 TEST_P(QuicReceivedPacketManagerTest,
        SendDelayedAckDecimationWithLargeReordering) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   QuicReceivedPacketManagerPeer::SetAckMode(&received_manager_,
                                             ACK_DECIMATION_WITH_REORDERING);
@@ -735,6 +747,9 @@
 
 TEST_P(QuicReceivedPacketManagerTest,
        SendDelayedAckDecimationWithReorderingEighthRtt) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   QuicReceivedPacketManagerPeer::SetAckMode(&received_manager_,
                                             ACK_DECIMATION_WITH_REORDERING);
@@ -776,6 +791,9 @@
 
 TEST_P(QuicReceivedPacketManagerTest,
        SendDelayedAckDecimationWithLargeReorderingEighthRtt) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   QuicReceivedPacketManagerPeer::SetAckMode(&received_manager_,
                                             ACK_DECIMATION_WITH_REORDERING);
diff --git a/quic/core/uber_received_packet_manager_test.cc b/quic/core/uber_received_packet_manager_test.cc
index a2fb640..41dadcb 100644
--- a/quic/core/uber_received_packet_manager_test.cc
+++ b/quic/core/uber_received_packet_manager_test.cc
@@ -349,6 +349,9 @@
 }
 
 TEST_F(UberReceivedPacketManagerTest, SendDelayedAfterQuiescence) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   UberReceivedPacketManagerPeer::SetFastAckAfterQuiescence(manager_.get(),
                                                            true);
@@ -429,6 +432,9 @@
 
 TEST_F(UberReceivedPacketManagerTest,
        SendDelayedAckAckDecimationAfterQuiescence) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   UberReceivedPacketManagerPeer::SetAckMode(manager_.get(), ACK_DECIMATION);
   UberReceivedPacketManagerPeer::SetFastAckAfterQuiescence(manager_.get(),
@@ -570,6 +576,9 @@
 }
 
 TEST_F(UberReceivedPacketManagerTest, SendDelayedAckDecimationWithReordering) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   UberReceivedPacketManagerPeer::SetAckMode(manager_.get(),
                                             ACK_DECIMATION_WITH_REORDERING);
@@ -613,6 +622,9 @@
 
 TEST_F(UberReceivedPacketManagerTest,
        SendDelayedAckDecimationWithLargeReordering) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   UberReceivedPacketManagerPeer::SetAckMode(manager_.get(),
                                             ACK_DECIMATION_WITH_REORDERING);
@@ -658,6 +670,9 @@
 
 TEST_F(UberReceivedPacketManagerTest,
        SendDelayedAckDecimationWithReorderingEighthRtt) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   UberReceivedPacketManagerPeer::SetAckMode(manager_.get(),
                                             ACK_DECIMATION_WITH_REORDERING);
@@ -698,6 +713,9 @@
 
 TEST_F(UberReceivedPacketManagerTest,
        SendDelayedAckDecimationWithLargeReorderingEighthRtt) {
+  if (GetQuicReloadableFlag(quic_remove_unused_ack_options)) {
+    return;
+  }
   EXPECT_FALSE(HasPendingAck());
   UberReceivedPacketManagerPeer::SetAckMode(manager_.get(),
                                             ACK_DECIMATION_WITH_REORDERING);