diff --git a/quic/core/http/end_to_end_test.cc b/quic/core/http/end_to_end_test.cc
index 52c8d82..2f54a3c 100644
--- a/quic/core/http/end_to_end_test.cc
+++ b/quic/core/http/end_to_end_test.cc
@@ -247,7 +247,6 @@
         support_server_push_(false),
         expected_server_connection_id_length_(kQuicDefaultConnectionIdLength) {
     SetQuicReloadableFlag(quic_supports_tls_handshake, true);
-    SetQuicReloadableFlag(quic_simplify_stop_waiting, true);
     client_supported_versions_ = GetParam().client_supported_versions;
     server_supported_versions_ = GetParam().server_supported_versions;
     negotiated_version_ = GetParam().negotiated_version;
diff --git a/quic/core/quic_connection.cc b/quic/core/quic_connection.cc
index bf100c5..06f1ebb 100644
--- a/quic/core/quic_connection.cc
+++ b/quic/core/quic_connection.cc
@@ -1037,12 +1037,8 @@
   // If the incoming ack's packets set expresses received packets: peer is still
   // acking packets which we never care about.
   // Send an ack to raise the high water mark.
-  bool send_stop_waiting = GetLeastUnacked() > start;
-  if (GetQuicReloadableFlag(quic_simplify_stop_waiting) &&
-      no_stop_waiting_frames_) {
-    QUIC_RELOADABLE_FLAG_COUNT(quic_simplify_stop_waiting);
-    send_stop_waiting = false;
-  }
+  const bool send_stop_waiting =
+      no_stop_waiting_frames_ ? false : GetLeastUnacked() > start;
   PostProcessAfterAckFrame(send_stop_waiting,
                            ack_result == PACKETS_NEWLY_ACKED);
   processing_ack_frame_ = false;
diff --git a/quic/core/quic_connection.h b/quic/core/quic_connection.h
index 7098cc8..9c57f86 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -1292,7 +1292,7 @@
 
   // Indicates how many consecutive times an ack has arrived which indicates
   // the peer needs to stop waiting for some packets.
-  // TODO(fayang): remove this when deprecating quic_simplify_stop_waiting.
+  // TODO(fayang): remove this when deprecating QUIC_VERSION_43.
   int stop_waiting_count_;
 
   // Indicates the retransmission alarm needs to be set.
diff --git a/quic/core/quic_connection_test.cc b/quic/core/quic_connection_test.cc
index 24faad8..b6aa85e 100644
--- a/quic/core/quic_connection_test.cc
+++ b/quic/core/quic_connection_test.cc
@@ -2687,18 +2687,13 @@
   connection_.SendStreamDataWithString(3, "foofoofoo", 9, NO_FIN);
   // Ack bundled.
   if (GetParam().no_stop_waiting) {
-    if (GetQuicReloadableFlag(quic_simplify_stop_waiting)) {
-      // Do not ACK acks.
-      EXPECT_EQ(1u, writer_->frame_count());
-    } else {
-      EXPECT_EQ(2u, writer_->frame_count());
-    }
+    // Do not ACK acks.
+    EXPECT_EQ(1u, writer_->frame_count());
   } else {
     EXPECT_EQ(3u, writer_->frame_count());
   }
   EXPECT_EQ(1u, writer_->stream_frames().size());
-  if (GetParam().no_stop_waiting &&
-      GetQuicReloadableFlag(quic_simplify_stop_waiting)) {
+  if (GetParam().no_stop_waiting) {
     EXPECT_TRUE(writer_->ack_frames().empty());
   } else {
     EXPECT_FALSE(writer_->ack_frames().empty());
@@ -6927,19 +6922,13 @@
   // Check that ack is bundled with outgoing data and the delayed ack
   // alarm is reset.
   if (GetParam().no_stop_waiting) {
-    if (GetQuicReloadableFlag(quic_simplify_stop_waiting)) {
-      // Do not ACK acks.
-      EXPECT_EQ(1u, writer_->frame_count());
-    } else {
-      EXPECT_EQ(2u, writer_->frame_count());
-      EXPECT_TRUE(writer_->stop_waiting_frames().empty());
-    }
+    // Do not ACK acks.
+    EXPECT_EQ(1u, writer_->frame_count());
   } else {
     EXPECT_EQ(3u, writer_->frame_count());
     EXPECT_FALSE(writer_->stop_waiting_frames().empty());
   }
-  if (GetParam().no_stop_waiting &&
-      GetQuicReloadableFlag(quic_simplify_stop_waiting)) {
+  if (GetParam().no_stop_waiting) {
     EXPECT_TRUE(writer_->ack_frames().empty());
   } else {
     EXPECT_FALSE(writer_->ack_frames().empty());
@@ -8406,12 +8395,8 @@
   connection_.GetPingAlarm()->Fire();
   size_t padding_frame_count = writer_->padding_frames().size();
   if (GetParam().no_stop_waiting) {
-    if (GetQuicReloadableFlag(quic_simplify_stop_waiting)) {
-      // Do not ACK acks.
-      EXPECT_EQ(padding_frame_count + 1u, writer_->frame_count());
-    } else {
-      EXPECT_EQ(padding_frame_count + 2u, writer_->frame_count());
-    }
+    // Do not ACK acks.
+    EXPECT_EQ(padding_frame_count + 1u, writer_->frame_count());
   } else {
     EXPECT_EQ(padding_frame_count + 3u, writer_->frame_count());
   }
diff --git a/quic/core/quic_versions.cc b/quic/core/quic_versions.cc
index e2996f6..57bd3fa 100644
--- a/quic/core/quic_versions.cc
+++ b/quic/core/quic_versions.cc
@@ -459,7 +459,6 @@
 void QuicVersionInitializeSupportForIetfDraft() {
   // Enable necessary flags.
   SetQuicReloadableFlag(quic_supports_tls_handshake, true);
-  SetQuicReloadableFlag(quic_simplify_stop_waiting, true);
 }
 
 void QuicEnableVersion(ParsedQuicVersion parsed_version) {