diff --git a/quic/core/crypto/transport_parameters.cc b/quic/core/crypto/transport_parameters.cc
index 75d4323..dcd2fc9 100644
--- a/quic/core/crypto/transport_parameters.cc
+++ b/quic/core/crypto/transport_parameters.cc
@@ -156,11 +156,12 @@
     case TransportParameters::kMaxDatagramFrameSize:
     case TransportParameters::kInitialRoundTripTime:
     case TransportParameters::kGoogleConnectionOptions:
-    case TransportParameters::kGoogleUserAgentId:
     case TransportParameters::kGoogleKeyUpdateNotYetSupported:
     case TransportParameters::kGoogleQuicVersion:
     case TransportParameters::kMinAckDelay:
       return true;
+    case TransportParameters::kGoogleUserAgentId:
+      return !GetQuicReloadableFlag(quic_ignore_user_agent_transport_parameter);
   }
   return false;
 }
@@ -1327,6 +1328,22 @@
         }
       } break;
       case TransportParameters::kGoogleUserAgentId:
+        if (GetQuicReloadableFlag(quic_ignore_user_agent_transport_parameter)) {
+          QUIC_RELOADABLE_FLAG_COUNT(
+              quic_ignore_user_agent_transport_parameter);
+          // This is a copy of the default switch statement below.
+          // TODO(dschinazi) remove this case entirely when deprecating the
+          // quic_ignore_user_agent_transport_parameter flag.
+          if (out->custom_parameters.find(param_id) !=
+              out->custom_parameters.end()) {
+            *error_details = "Received a second unknown parameter" +
+                             TransportParameterIdToString(param_id);
+            return false;
+          }
+          out->custom_parameters[param_id] =
+              std::string(value_reader.ReadRemainingPayload());
+          break;
+        }
         if (out->user_agent_id.has_value()) {
           *error_details = "Received a second user_agent_id";
           return false;
diff --git a/quic/core/crypto/transport_parameters_test.cc b/quic/core/crypto/transport_parameters_test.cc
index 48af1c4..a758d81 100644
--- a/quic/core/crypto/transport_parameters_test.cc
+++ b/quic/core/crypto/transport_parameters_test.cc
@@ -282,7 +282,9 @@
       CreateFakeInitialSourceConnectionId();
   orig_params.initial_round_trip_time_us.set_value(kFakeInitialRoundTripTime);
   orig_params.google_connection_options = CreateFakeGoogleConnectionOptions();
-  orig_params.user_agent_id = CreateFakeUserAgentId();
+  if (!GetQuicReloadableFlag(quic_ignore_user_agent_transport_parameter)) {
+    orig_params.user_agent_id = CreateFakeUserAgentId();
+  }
   orig_params.key_update_not_yet_supported = kFakeKeyUpdateNotYetSupported;
   orig_params.custom_parameters[kCustomParameter1] = kCustomParameter1Value;
   orig_params.custom_parameters[kCustomParameter2] = kCustomParameter2Value;
@@ -581,8 +583,12 @@
   ASSERT_TRUE(new_params.google_connection_options.has_value());
   EXPECT_EQ(CreateFakeGoogleConnectionOptions(),
             new_params.google_connection_options.value());
-  ASSERT_TRUE(new_params.user_agent_id.has_value());
-  EXPECT_EQ(CreateFakeUserAgentId(), new_params.user_agent_id.value());
+  if (!GetQuicReloadableFlag(quic_ignore_user_agent_transport_parameter)) {
+    ASSERT_TRUE(new_params.user_agent_id.has_value());
+    EXPECT_EQ(CreateFakeUserAgentId(), new_params.user_agent_id.value());
+  } else {
+    EXPECT_FALSE(new_params.user_agent_id.has_value());
+  }
   EXPECT_TRUE(new_params.key_update_not_yet_supported);
 }
 
diff --git a/quic/core/http/end_to_end_test.cc b/quic/core/http/end_to_end_test.cc
index ba3c7a7..3b073af 100644
--- a/quic/core/http/end_to_end_test.cc
+++ b/quic/core/http/end_to_end_test.cc
@@ -547,8 +547,12 @@
           EXPECT_EQ(0u, server_stats.packets_lost);
         }
         EXPECT_EQ(0u, server_stats.packets_discarded);
-        EXPECT_EQ(server_session->user_agent_id().value_or("MissingUserAgent"),
-                  kTestUserAgentId);
+        if (!GetQuicReloadableFlag(
+                quic_ignore_user_agent_transport_parameter)) {
+          EXPECT_EQ(
+              server_session->user_agent_id().value_or("MissingUserAgent"),
+              kTestUserAgentId);
+        }
       } else {
         ADD_FAILURE() << "Missing server connection";
       }
@@ -5594,8 +5598,10 @@
   QuicConfig* server_config = nullptr;
   if (server_session != nullptr) {
     server_config = server_session->config();
-    EXPECT_EQ(server_session->user_agent_id().value_or("MissingUserAgent"),
-              kTestUserAgentId);
+    if (!GetQuicReloadableFlag(quic_ignore_user_agent_transport_parameter)) {
+      EXPECT_EQ(server_session->user_agent_id().value_or("MissingUserAgent"),
+                kTestUserAgentId);
+    }
   } else {
     ADD_FAILURE() << "Missing server session";
   }
diff --git a/quic/core/quic_flags_list.h b/quic/core/quic_flags_list.h
index 994bbdd..b40bd6c 100644
--- a/quic/core/quic_flags_list.h
+++ b/quic/core/quic_flags_list.h
@@ -121,6 +121,8 @@
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_match_ietf_reset_code, false)
 // When the flag is true, exit STARTUP after the same number of loss events as PROBE_UP.
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_bbr2_startup_probe_up_loss_events, true)
+// When true, QUIC server will ignore received user agent transport parameter and rely on getting that information from HTTP headers.
+QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_ignore_user_agent_transport_parameter, false)
 // When true, QuicDispatcher will silently drop incoming packets whose UDP source port is on the blocklist.
 QUIC_FLAG(FLAGS_quic_reloadable_flag_quic_blocked_ports, false)
 // When true, defaults to BBR congestion control instead of Cubic.