diff --git a/quic/core/frames/quic_stop_sending_frame.cc b/quic/core/frames/quic_stop_sending_frame.cc
index 20281e5..256210f 100644
--- a/quic/core/frames/quic_stop_sending_frame.cc
+++ b/quic/core/frames/quic_stop_sending_frame.cc
@@ -13,13 +13,7 @@
       stream_id(stream_id),
       error_code(error_code),
       ietf_error_code(
-          GetQuicReloadableFlag(quic_stop_sending_uses_ietf_error_code)
-              ? RstStreamErrorCodeToIetfResetStreamErrorCode(error_code)
-              : static_cast<uint64_t>(error_code)) {
-  if (GetQuicReloadableFlag(quic_stop_sending_uses_ietf_error_code)) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_stop_sending_uses_ietf_error_code, 1, 2);
-  }
-}
+          RstStreamErrorCodeToIetfResetStreamErrorCode(error_code)) {}
 
 std::ostream& operator<<(std::ostream& os, const QuicStopSendingFrame& frame) {
   os << "{ control_frame_id: " << frame.control_frame_id
diff --git a/quic/core/http/quic_spdy_session.cc b/quic/core/http/quic_spdy_session.cc
index 438352a..af11a1f 100644
--- a/quic/core/http/quic_spdy_session.cc
+++ b/quic/core/http/quic_spdy_session.cc
@@ -1320,13 +1320,7 @@
       return true;
     }
     default:
-      if (GetQuicReloadableFlag(quic_stop_sending_uses_ietf_error_code)) {
-        SendStopSending(QUIC_STREAM_STREAM_CREATION_ERROR, pending->id());
-      } else {
-        SendStopSending(static_cast<QuicRstStreamErrorCode>(
-                            QuicHttp3ErrorCode::STREAM_CREATION_ERROR),
-                        pending->id());
-      }
+      SendStopSending(QUIC_STREAM_STREAM_CREATION_ERROR, pending->id());
       pending->StopReading();
   }
   return false;
diff --git a/quic/core/http/quic_spdy_session_test.cc b/quic/core/http/quic_spdy_session_test.cc
index d1e271c..3b8db73 100644
--- a/quic/core/http/quic_spdy_session_test.cc
+++ b/quic/core/http/quic_spdy_session_test.cc
@@ -2335,12 +2335,8 @@
 
           QuicStopSendingFrame* stop_sending = frame.stop_sending_frame;
           EXPECT_EQ(stream_id, stop_sending->stream_id);
-          EXPECT_EQ(
-              GetQuicReloadableFlag(quic_stop_sending_uses_ietf_error_code)
-                  ? QUIC_STREAM_STREAM_CREATION_ERROR
-                  : static_cast<QuicRstStreamErrorCode>(
-                        QuicHttp3ErrorCode::STREAM_CREATION_ERROR),
-              stop_sending->error_code);
+          EXPECT_EQ(QUIC_STREAM_STREAM_CREATION_ERROR,
+                    stop_sending->error_code);
           EXPECT_EQ(
               static_cast<uint64_t>(QuicHttp3ErrorCode::STREAM_CREATION_ERROR),
               stop_sending->ietf_error_code);
diff --git a/quic/core/quic_flags_list.h b/quic/core/quic_flags_list.h
index ae001f7..4ddf2d8 100644
--- a/quic/core/quic_flags_list.h
+++ b/quic/core/quic_flags_list.h
@@ -69,7 +69,6 @@
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_single_ack_in_packet, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_split_up_send_rst_2, true)
 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)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_testonly_default_false, false)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_testonly_default_true, true)
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_tls_use_early_select_cert, false)
diff --git a/quic/core/quic_framer.cc b/quic/core/quic_framer.cc
index 90f4370..98c0dd7 100644
--- a/quic/core/quic_framer.cc
+++ b/quic/core/quic_framer.cc
@@ -6075,24 +6075,8 @@
     return false;
   }
 
-  if (GetQuicReloadableFlag(quic_stop_sending_uses_ietf_error_code)) {
-    QUIC_RELOADABLE_FLAG_COUNT_N(quic_stop_sending_uses_ietf_error_code, 2, 2);
-    stop_sending_frame->error_code =
-        IetfResetStreamErrorCodeToRstStreamErrorCode(
-            stop_sending_frame->ietf_error_code);
-    return true;
-  }
-
-  // TODO(fkastenholz): when error codes go to uint64_t, remove this.
-  if (stop_sending_frame->ietf_error_code > 0xffff) {
-    stop_sending_frame->error_code =
-        static_cast<QuicRstStreamErrorCode>(0xffff);
-    QUIC_DLOG(ERROR) << "Stop sending error code ("
-                     << stop_sending_frame->ietf_error_code << ") > 0xffff";
-  } else {
-    stop_sending_frame->error_code = static_cast<QuicRstStreamErrorCode>(
-        stop_sending_frame->ietf_error_code);
-  }
+  stop_sending_frame->error_code = IetfResetStreamErrorCodeToRstStreamErrorCode(
+      stop_sending_frame->ietf_error_code);
   return true;
 }
 
diff --git a/quic/core/quic_framer_test.cc b/quic/core/quic_framer_test.cc
index ba9a70e..da6cd5a 100644
--- a/quic/core/quic_framer_test.cc
+++ b/quic/core/quic_framer_test.cc
@@ -11235,12 +11235,8 @@
       PACKET_8BYTE_CONNECTION_ID, PACKET_0BYTE_CONNECTION_ID));
 
   EXPECT_EQ(kStreamId, visitor_.stop_sending_frame_.stream_id);
-  if (GetQuicReloadableFlag(quic_stop_sending_uses_ietf_error_code)) {
-    EXPECT_EQ(QUIC_STREAM_UNKNOWN_APPLICATION_ERROR_CODE,
-              visitor_.stop_sending_frame_.error_code);
-  } else {
-    EXPECT_EQ(0x7654, visitor_.stop_sending_frame_.error_code);
-  }
+  EXPECT_EQ(QUIC_STREAM_UNKNOWN_APPLICATION_ERROR_CODE,
+            visitor_.stop_sending_frame_.error_code);
   EXPECT_EQ(static_cast<uint64_t>(0x7654),
             visitor_.stop_sending_frame_.ietf_error_code);