diff --git a/api/peer_connection_interface.h b/api/peer_connection_interface.h
index c367fae36d..d40d7a49c3 100644
--- a/api/peer_connection_interface.h
+++ b/api/peer_connection_interface.h
@@ -169,9 +169,16 @@ class StatsObserver : public rtc::RefCountInterface {
 };
 
 enum class SdpSemantics {
+  // TODO(https://crbug.com/webrtc/13528): Remove support for kPlanB.
   kPlanB_DEPRECATED,
   kPlanB [[deprecated]] = kPlanB_DEPRECATED,
-  kUnifiedPlan
+  kUnifiedPlan,
+  // The default SdpSemantics value is about to change to kUnifiedPlan. During a
+  // short transition period, kNotSpecified is used to ensure clients that don't
+  // set SdpSemantics are aware of the change by CHECK-crashing.
+  // TODO(https://crbug.com/webrtc/11121): When the default has changed to
+  // kUnifiedPlan, delete kNotSpecified.
+  kNotSpecified
 };
 
 class RTC_EXPORT PeerConnectionInterface : public rtc::RefCountInterface {
@@ -639,10 +646,17 @@ class RTC_EXPORT PeerConnectionInterface : public rtc::RefCountInterface {
     // the same media type.
     //
     // For users who have to interwork with legacy WebRTC implementations,
-    // it is possible to specify kPlanB until the code is finally removed.
+    // it is possible to specify kPlanB until the code is finally removed
+    // (https://crbug.com/webrtc/13528).
     //
     // For all other users, specify kUnifiedPlan.
-    SdpSemantics sdp_semantics = SdpSemantics::kPlanB_DEPRECATED;
+    //
+    // The default SdpSemantics value is about to change to kUnifiedPlan. During
+    // a short transition period, kNotSpecified is used to ensure clients that
+    // don't set SdpSemantics are aware of the change by CHECK-crashing.
+    // TODO(https://crbug.com/webrtc/11121): When the default has changed to
+    // kUnifiedPlan, delete kNotSpecified.
+    SdpSemantics sdp_semantics = SdpSemantics::kNotSpecified;
 
     // TODO(bugs.webrtc.org/9891) - Move to crypto_options or remove.
     // Actively reset the SRTP parameters whenever the DTLS transports
diff --git a/pc/peer_connection.cc b/pc/peer_connection.cc
index bd90711666..99828f8b49 100644
--- a/pc/peer_connection.cc
+++ b/pc/peer_connection.cc
@@ -418,6 +418,20 @@ RTCErrorOr<rtc::scoped_refptr<PeerConnection>> PeerConnection::Create(
     std::unique_ptr<Call> call,
     const PeerConnectionInterface::RTCConfiguration& configuration,
     PeerConnectionDependencies dependencies) {
+  // Prior to adding this CHECK, the default value was kPlanB. Because kPlanB is
+  // about to be deprecated in favor of the spec-compliant kUnifiedPlan, the
+  // default will soon change to kUnifiedPlan. This CHECK ensures that anybody
+  // implicitly relying on the default being kPlanB is made aware of the change.
+  // To avoid crashing, you can overwrite sdp_semantics to kPlanB for the old
+  // behavior, but you will need to migrate to kUnifiedPlan before kPlanB is
+  // removed.
+  // TODO(https://crbug.com/webrtc/11121): When the default is kUnifiedPlan,
+  // delete kNotSpecified.
+  // TODO(https://crbug.com/webrtc/13528): Remove support for kPlanB.
+  RTC_CHECK(configuration.sdp_semantics != SdpSemantics::kNotSpecified)
+      << "Please specify sdp_semantics. The default is about to change to "
+      << "kUnifiedPlan.";
+
   RTCError config_error = cricket::P2PTransportChannel::ValidateIceConfig(
       ParseIceConfig(configuration));
   if (!config_error.ok()) {
diff --git a/pc/peer_connection_factory_unittest.cc b/pc/peer_connection_factory_unittest.cc
index dd392c5ad2..c12b563e27 100644
--- a/pc/peer_connection_factory_unittest.cc
+++ b/pc/peer_connection_factory_unittest.cc
@@ -190,6 +190,7 @@ TEST(PeerConnectionFactoryTestInternal, DISABLED_CreatePCUsingInternalModules) {
 
   NullPeerConnectionObserver observer;
   webrtc::PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
 
   std::unique_ptr<FakeRTCCertificateGenerator> cert_generator(
       new FakeRTCCertificateGenerator());
@@ -269,6 +270,7 @@ TEST_F(PeerConnectionFactoryTest, CheckRtpReceiverDataCapabilities) {
 // configuration. Also verifies the URL's parsed correctly as expected.
 TEST_F(PeerConnectionFactoryTest, CreatePCUsingIceServers) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   webrtc::PeerConnectionInterface::IceServer ice_server;
   ice_server.uri = kStunIceServer;
   config.servers.push_back(ice_server);
@@ -304,6 +306,7 @@ TEST_F(PeerConnectionFactoryTest, CreatePCUsingIceServers) {
 // configuration. Also verifies the list of URL's parsed correctly as expected.
 TEST_F(PeerConnectionFactoryTest, CreatePCUsingIceServersUrls) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   webrtc::PeerConnectionInterface::IceServer ice_server;
   ice_server.urls.push_back(kStunIceServer);
   ice_server.urls.push_back(kTurnIceServer);
@@ -333,6 +336,7 @@ TEST_F(PeerConnectionFactoryTest, CreatePCUsingIceServersUrls) {
 
 TEST_F(PeerConnectionFactoryTest, CreatePCUsingNoUsernameInUri) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   webrtc::PeerConnectionInterface::IceServer ice_server;
   ice_server.uri = kStunIceServer;
   config.servers.push_back(ice_server);
@@ -357,6 +361,7 @@ TEST_F(PeerConnectionFactoryTest, CreatePCUsingNoUsernameInUri) {
 // has transport parameter in it.
 TEST_F(PeerConnectionFactoryTest, CreatePCUsingTurnUrlWithTransportParam) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   webrtc::PeerConnectionInterface::IceServer ice_server;
   ice_server.uri = kTurnIceServerWithTransport;
   ice_server.username = kTurnUsername;
@@ -377,6 +382,7 @@ TEST_F(PeerConnectionFactoryTest, CreatePCUsingTurnUrlWithTransportParam) {
 
 TEST_F(PeerConnectionFactoryTest, CreatePCUsingSecureTurnUrl) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   webrtc::PeerConnectionInterface::IceServer ice_server;
   ice_server.uri = kSecureTurnIceServer;
   ice_server.username = kTurnUsername;
@@ -414,6 +420,7 @@ TEST_F(PeerConnectionFactoryTest, CreatePCUsingSecureTurnUrl) {
 
 TEST_F(PeerConnectionFactoryTest, CreatePCUsingIPLiteralAddress) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
   webrtc::PeerConnectionInterface::IceServer ice_server;
   ice_server.uri = kStunIceServerWithIPv4Address;
   config.servers.push_back(ice_server);
diff --git a/pc/peer_connection_histogram_unittest.cc b/pc/peer_connection_histogram_unittest.cc
index 8a1aa60700..27bae854d6 100644
--- a/pc/peer_connection_histogram_unittest.cc
+++ b/pc/peer_connection_histogram_unittest.cc
@@ -243,8 +243,10 @@ class PeerConnectionUsageHistogramTest : public ::testing::Test {
   }
 
   WrapperPtr CreatePeerConnection() {
+    RTCConfiguration config;
+    config.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
     return CreatePeerConnection(
-        RTCConfiguration(), PeerConnectionFactoryInterface::Options(), nullptr);
+        config, PeerConnectionFactoryInterface::Options(), nullptr);
   }
 
   WrapperPtr CreatePeerConnection(const RTCConfiguration& config) {
@@ -275,6 +277,7 @@ class PeerConnectionUsageHistogramTest : public ::testing::Test {
 
   WrapperPtr CreatePeerConnectionWithImmediateReport() {
     RTCConfiguration configuration;
+    configuration.sdp_semantics = webrtc::SdpSemantics::kUnifiedPlan;
     configuration.report_usage_pattern_delay_ms = 0;
     return CreatePeerConnection(
         configuration, PeerConnectionFactoryInterface::Options(), nullptr);
@@ -287,7 +290,9 @@ class PeerConnectionUsageHistogramTest : public ::testing::Test {
 
     auto port_allocator =
         std::make_unique<cricket::BasicPortAllocator>(fake_network);
-    return CreatePeerConnection(RTCConfiguration(),
+    RTCConfiguration config;
+    config.sdp_semantics = SdpSemantics::kUnifiedPlan;
+    return CreatePeerConnection(config,
                                 PeerConnectionFactoryInterface::Options(),
                                 std::move(port_allocator));
   }
@@ -300,7 +305,9 @@ class PeerConnectionUsageHistogramTest : public ::testing::Test {
     auto port_allocator =
         std::make_unique<cricket::BasicPortAllocator>(fake_network);
 
-    return CreatePeerConnection(RTCConfiguration(),
+    RTCConfiguration config;
+    config.sdp_semantics = SdpSemantics::kUnifiedPlan;
+    return CreatePeerConnection(config,
                                 PeerConnectionFactoryInterface::Options(),
                                 std::move(port_allocator));
   }
@@ -420,6 +427,7 @@ TEST_F(PeerConnectionUsageHistogramTest, FingerprintAudioVideo) {
 // candidate.
 TEST_F(PeerConnectionUsageHistogramTest, FingerprintWithMdnsCaller) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
 
   // Enable hostname candidates with mDNS names.
   auto caller = CreatePeerConnectionWithMdns(config);
@@ -461,6 +469,7 @@ TEST_F(PeerConnectionUsageHistogramTest, FingerprintWithMdnsCaller) {
 // candidate.
 TEST_F(PeerConnectionUsageHistogramTest, FingerprintWithMdnsCallee) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
 
   // Enable hostname candidates with mDNS names.
   auto caller = CreatePeerConnection(config);
@@ -526,6 +535,7 @@ TEST_F(PeerConnectionUsageHistogramTest, FingerprintDataOnly) {
 
 TEST_F(PeerConnectionUsageHistogramTest, FingerprintStunTurn) {
   RTCConfiguration configuration;
+  configuration.sdp_semantics = SdpSemantics::kUnifiedPlan;
   PeerConnection::IceServer server;
   server.urls = {"stun:dummy.stun.server"};
   configuration.servers.push_back(server);
@@ -546,6 +556,7 @@ TEST_F(PeerConnectionUsageHistogramTest, FingerprintStunTurn) {
 
 TEST_F(PeerConnectionUsageHistogramTest, FingerprintStunTurnInReconfiguration) {
   RTCConfiguration configuration;
+  configuration.sdp_semantics = SdpSemantics::kUnifiedPlan;
   PeerConnection::IceServer server;
   server.urls = {"stun:dummy.stun.server"};
   configuration.servers.push_back(server);
@@ -641,7 +652,9 @@ TEST_F(PeerConnectionUsageHistogramTest,
   // signaled and we expect a connection with prflx remote candidates at the
   // caller side.
   auto caller = CreatePeerConnectionWithPrivateIpv6LocalAddresses();
-  auto callee = CreatePeerConnectionWithMdns(RTCConfiguration());
+  RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
+  auto callee = CreatePeerConnectionWithMdns(config);
   caller->CreateDataChannel("test_channel");
   ASSERT_TRUE(caller->SetLocalDescription(caller->CreateOffer()));
   // Wait until the gathering completes so that the session description would
diff --git a/pc/peer_connection_ice_unittest.cc b/pc/peer_connection_ice_unittest.cc
index 112d8dfe6a..49a79a2556 100644
--- a/pc/peer_connection_ice_unittest.cc
+++ b/pc/peer_connection_ice_unittest.cc
@@ -844,6 +844,7 @@ TEST_P(PeerConnectionIceTest, LocalDescriptionUpdatedWhenContinualGathering) {
   const SocketAddress kLocalAddress("1.1.1.1", 0);
 
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.continual_gathering_policy =
       PeerConnectionInterface::GATHER_CONTINUALLY;
   auto caller = CreatePeerConnectionWithAudioVideo(config);
@@ -866,6 +867,7 @@ TEST_P(PeerConnectionIceTest,
   const SocketAddress kLocalAddress("1.1.1.1", 0);
 
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.continual_gathering_policy =
       PeerConnectionInterface::GATHER_CONTINUALLY;
   auto caller = CreatePeerConnectionWithAudioVideo(config);
@@ -892,6 +894,7 @@ TEST_P(PeerConnectionIceTest,
   const SocketAddress kLocalAddress("1.1.1.1", 0);
 
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.continual_gathering_policy = PeerConnectionInterface::GATHER_ONCE;
   auto caller = CreatePeerConnectionWithAudioVideo(config);
   caller->network()->AddInterface(kLocalAddress);
@@ -1392,6 +1395,7 @@ class PeerConnectionIceConfigTest : public ::testing::Test {
 
 TEST_F(PeerConnectionIceConfigTest, SetStunCandidateKeepaliveInterval) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.stun_candidate_keepalive_interval = 123;
   config.ice_candidate_pool_size = 1;
   CreatePeerConnection(config);
@@ -1408,6 +1412,7 @@ TEST_F(PeerConnectionIceConfigTest, SetStunCandidateKeepaliveInterval) {
 
 TEST_F(PeerConnectionIceConfigTest, SetStableWritableConnectionInterval) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.stable_writable_connection_ping_interval_ms = 3500;
   CreatePeerConnection(config);
   EXPECT_TRUE(pc_->SetConfiguration(config).ok());
@@ -1418,6 +1423,7 @@ TEST_F(PeerConnectionIceConfigTest, SetStableWritableConnectionInterval) {
 TEST_F(PeerConnectionIceConfigTest,
        SetStableWritableConnectionInterval_FailsValidation) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   CreatePeerConnection(config);
   ASSERT_TRUE(pc_->SetConfiguration(config).ok());
   config.stable_writable_connection_ping_interval_ms = 5000;
@@ -1428,6 +1434,7 @@ TEST_F(PeerConnectionIceConfigTest,
 TEST_F(PeerConnectionIceConfigTest,
        SetStableWritableConnectionInterval_DefaultValue_FailsValidation) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   CreatePeerConnection(config);
   ASSERT_TRUE(pc_->SetConfiguration(config).ok());
   config.ice_check_interval_strong_connectivity = 2500;
@@ -1438,6 +1445,7 @@ TEST_F(PeerConnectionIceConfigTest,
 
 TEST_P(PeerConnectionIceTest, IceCredentialsCreateOffer) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.ice_candidate_pool_size = 1;
   auto pc = CreatePeerConnectionWithAudioVideo(config);
   ASSERT_NE(pc->port_allocator_, nullptr);
@@ -1455,6 +1463,7 @@ TEST_P(PeerConnectionIceTest, IceCredentialsCreateOffer) {
 
 TEST_P(PeerConnectionIceTest, IceCredentialsCreateAnswer) {
   RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   config.ice_candidate_pool_size = 1;
   auto pc = CreatePeerConnectionWithAudioVideo(config);
   ASSERT_NE(pc->port_allocator_, nullptr);
diff --git a/pc/peer_connection_interface_unittest.cc b/pc/peer_connection_interface_unittest.cc
index 3aaae64be3..44f135ffab 100644
--- a/pc/peer_connection_interface_unittest.cc
+++ b/pc/peer_connection_interface_unittest.cc
@@ -1332,6 +1332,7 @@ TEST_P(PeerConnectionInterfaceTest,
 // in the RTCConfiguration.
 TEST_P(PeerConnectionInterfaceTest, CreatePeerConnectionWithPooledCandidates) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   PeerConnectionInterface::IceServer server;
   server.uri = kStunAddressOnly;
   config.servers.push_back(server);
@@ -1375,6 +1376,7 @@ TEST_P(PeerConnectionInterfaceTest,
   // Create RTCConfiguration with some network-related fields relevant to
   // PortAllocator populated.
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.disable_ipv6_on_wifi = true;
   config.max_ipv6_networks = 10;
   config.tcp_candidate_policy =
@@ -1415,6 +1417,7 @@ TEST_P(PeerConnectionInterfaceTest,
 // constructed with, before SetConfiguration is called.
 TEST_P(PeerConnectionInterfaceTest, GetConfigurationAfterCreatePeerConnection) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.type = PeerConnectionInterface::kRelay;
   CreatePeerConnection(config);
 
@@ -1427,6 +1430,7 @@ TEST_P(PeerConnectionInterfaceTest, GetConfigurationAfterCreatePeerConnection) {
 // SetConfiguration.
 TEST_P(PeerConnectionInterfaceTest, GetConfigurationAfterSetConfiguration) {
   PeerConnectionInterface::RTCConfiguration starting_config;
+  starting_config.sdp_semantics = sdp_semantics_;
   starting_config.bundle_policy =
       webrtc::PeerConnection::kBundlePolicyMaxBundle;
   CreatePeerConnection(starting_config);
@@ -3009,6 +3013,7 @@ TEST_P(PeerConnectionInterfaceTest, OnAddTrackCallback) {
 // changing, the next offer causes an ICE restart.
 TEST_P(PeerConnectionInterfaceTest, SetConfigurationCausingIceRestart) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.type = PeerConnectionInterface::kRelay;
   CreatePeerConnection(config);
   config = pc_->GetConfiguration();
@@ -3043,6 +3048,7 @@ TEST_P(PeerConnectionInterfaceTest, SetConfigurationCausingIceRestart) {
 // changing, the next offer does *not* cause an ICE restart.
 TEST_P(PeerConnectionInterfaceTest, SetConfigurationNotCausingIceRestart) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.type = PeerConnectionInterface::kRelay;
   CreatePeerConnection(config);
   config = pc_->GetConfiguration();
@@ -3077,6 +3083,7 @@ TEST_P(PeerConnectionInterfaceTest, SetConfigurationNotCausingIceRestart) {
 //    that was already restarted.
 TEST_P(PeerConnectionInterfaceTest, SetConfigurationCausingPartialIceRestart) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.type = PeerConnectionInterface::kRelay;
   CreatePeerConnection(config);
   config = pc_->GetConfiguration();
@@ -3237,6 +3244,7 @@ TEST_P(PeerConnectionInterfaceTest, OffersAndAnswersHaveTrickleIceOption) {
 // RTCConfiguration.
 TEST_P(PeerConnectionInterfaceTest, IceRenominationNotOffered) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.enable_ice_renomination = false;
   CreatePeerConnection(config);
   AddAudioTrack("foo");
@@ -3253,6 +3261,7 @@ TEST_P(PeerConnectionInterfaceTest, IceRenominationNotOffered) {
 // if it's enabled in the PC's RTCConfiguration.
 TEST_P(PeerConnectionInterfaceTest, IceRenominationOptionInOfferAndAnswer) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.enable_ice_renomination = true;
   CreatePeerConnection(config);
   AddAudioTrack("foo");
@@ -3337,6 +3346,7 @@ TEST_P(PeerConnectionInterfaceTest,
        DISABLED_DataChannelOnlyOfferWithMaxBundlePolicy) {
 #endif  // WEBRTC_HAVE_SCTP
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = sdp_semantics_;
   config.bundle_policy = PeerConnectionInterface::kBundlePolicyMaxBundle;
   CreatePeerConnection(config);
 
@@ -3676,6 +3686,7 @@ class PeerConnectionMediaConfigTest : public ::testing::Test {
 // This sanity check validates the test infrastructure itself.
 TEST_F(PeerConnectionMediaConfigTest, TestCreateAndClose) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   rtc::scoped_refptr<PeerConnectionInterface> pc(
       pcf_->CreatePeerConnection(config, nullptr, nullptr, &observer_));
   EXPECT_TRUE(pc.get());
@@ -3688,6 +3699,7 @@ TEST_F(PeerConnectionMediaConfigTest, TestCreateAndClose) {
 // default RTCConfiguration.
 TEST_F(PeerConnectionMediaConfigTest, TestDefaults) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
 
   const cricket::MediaConfig& media_config = TestCreatePeerConnection(config);
 
@@ -3702,6 +3714,7 @@ TEST_F(PeerConnectionMediaConfigTest, TestDefaults) {
 // propagated from RTCConfiguration to the PeerConnection.
 TEST_F(PeerConnectionMediaConfigTest, TestDisablePrerendererSmoothingTrue) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
 
   config.set_prerenderer_smoothing(false);
   const cricket::MediaConfig& media_config = TestCreatePeerConnection(config);
@@ -3713,6 +3726,7 @@ TEST_F(PeerConnectionMediaConfigTest, TestDisablePrerendererSmoothingTrue) {
 // propagated from RTCConfiguration to the PeerConnection.
 TEST_F(PeerConnectionMediaConfigTest, TestEnableExperimentCpuLoadEstimator) {
   PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
 
   config.set_experiment_cpu_load_estimator(true);
   const cricket::MediaConfig& media_config = TestCreatePeerConnection(config);
diff --git a/pc/peer_connection_rampup_tests.cc b/pc/peer_connection_rampup_tests.cc
index d845b57cb3..692ca9d689 100644
--- a/pc/peer_connection_rampup_tests.cc
+++ b/pc/peer_connection_rampup_tests.cc
@@ -344,9 +344,11 @@ TEST_F(PeerConnectionRampUpTest, Bwe_After_TurnOverTCP) {
   ice_server.username = "test";
   ice_server.password = "test";
   PeerConnectionInterface::RTCConfiguration client_1_config;
+  client_1_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_1_config.servers.push_back(ice_server);
   client_1_config.type = PeerConnectionInterface::kRelay;
   PeerConnectionInterface::RTCConfiguration client_2_config;
+  client_2_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_2_config.servers.push_back(ice_server);
   client_2_config.type = PeerConnectionInterface::kRelay;
   ASSERT_TRUE(CreatePeerConnectionWrappers(client_1_config, client_2_config));
@@ -365,9 +367,11 @@ TEST_F(PeerConnectionRampUpTest, Bwe_After_TurnOverUDP) {
   ice_server.username = "test";
   ice_server.password = "test";
   PeerConnectionInterface::RTCConfiguration client_1_config;
+  client_1_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_1_config.servers.push_back(ice_server);
   client_1_config.type = PeerConnectionInterface::kRelay;
   PeerConnectionInterface::RTCConfiguration client_2_config;
+  client_2_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_2_config.servers.push_back(ice_server);
   client_2_config.type = PeerConnectionInterface::kRelay;
   ASSERT_TRUE(CreatePeerConnectionWrappers(client_1_config, client_2_config));
@@ -386,9 +390,11 @@ TEST_F(PeerConnectionRampUpTest, Bwe_After_TurnOverTLS) {
   ice_server.username = "test";
   ice_server.password = "test";
   PeerConnectionInterface::RTCConfiguration client_1_config;
+  client_1_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_1_config.servers.push_back(ice_server);
   client_1_config.type = PeerConnectionInterface::kRelay;
   PeerConnectionInterface::RTCConfiguration client_2_config;
+  client_2_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_2_config.servers.push_back(ice_server);
   client_2_config.type = PeerConnectionInterface::kRelay;
 
@@ -400,9 +406,11 @@ TEST_F(PeerConnectionRampUpTest, Bwe_After_TurnOverTLS) {
 
 TEST_F(PeerConnectionRampUpTest, Bwe_After_UDPPeerToPeer) {
   PeerConnectionInterface::RTCConfiguration client_1_config;
+  client_1_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_1_config.tcp_candidate_policy =
       PeerConnection::kTcpCandidatePolicyDisabled;
   PeerConnectionInterface::RTCConfiguration client_2_config;
+  client_2_config.sdp_semantics = SdpSemantics::kUnifiedPlan;
   client_2_config.tcp_candidate_policy =
       PeerConnection::kTcpCandidatePolicyDisabled;
   ASSERT_TRUE(CreatePeerConnectionWrappers(client_1_config, client_2_config));
@@ -413,9 +421,9 @@ TEST_F(PeerConnectionRampUpTest, Bwe_After_UDPPeerToPeer) {
 
 TEST_F(PeerConnectionRampUpTest, Bwe_After_TCPPeerToPeer) {
   firewall_socket_server()->set_udp_sockets_enabled(false);
-  ASSERT_TRUE(CreatePeerConnectionWrappers(
-      PeerConnectionInterface::RTCConfiguration(),
-      PeerConnectionInterface::RTCConfiguration()));
+  PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = SdpSemantics::kUnifiedPlan;
+  ASSERT_TRUE(CreatePeerConnectionWrappers(config, config));
 
   SetupOneWayCall();
   RunTest("tcp_peer_to_peer");
diff --git a/pc/rtc_stats_integrationtest.cc b/pc/rtc_stats_integrationtest.cc
index ca0df26bb0..ad533499ab 100644
--- a/pc/rtc_stats_integrationtest.cc
+++ b/pc/rtc_stats_integrationtest.cc
@@ -123,6 +123,7 @@ class RTCStatsIntegrationTest : public ::testing::Test {
   void StartCall() {
     // Create PeerConnections and "connect" sigslots
     PeerConnectionInterface::RTCConfiguration config;
+    config.sdp_semantics = SdpSemantics::kUnifiedPlan;
     PeerConnectionInterface::IceServer ice_server;
     ice_server.uri = "stun:1.1.1.1:3478";
     config.servers.push_back(ice_server);
diff --git a/pc/test/integration_test_helpers.h b/pc/test/integration_test_helpers.h
index fb59092496..dd935429de 100644
--- a/pc/test/integration_test_helpers.h
+++ b/pc/test/integration_test_helpers.h
@@ -774,6 +774,7 @@ class PeerConnectionIntegrationWrapper : public webrtc::PeerConnectionObserver,
       const PeerConnectionInterface::RTCConfiguration* config,
       webrtc::PeerConnectionDependencies dependencies) {
     PeerConnectionInterface::RTCConfiguration modified_config;
+    modified_config.sdp_semantics = sdp_semantics_;
     // If `config` is null, this will result in a default configuration being
     // used.
     if (config) {
diff --git a/sdk/objc/api/peerconnection/RTCConfiguration.mm b/sdk/objc/api/peerconnection/RTCConfiguration.mm
index 2b6e4ec848..0885e96f4e 100644
--- a/sdk/objc/api/peerconnection/RTCConfiguration.mm
+++ b/sdk/objc/api/peerconnection/RTCConfiguration.mm
@@ -17,6 +17,7 @@
 #import "RTCIceServer+Private.h"
 #import "base/RTCLogging.h"
 
+#include "rtc_base/checks.h"
 #include "rtc_base/rtc_certificate_generator.h"
 #include "rtc_base/ssl_identity.h"
 
@@ -67,6 +68,7 @@
 - (instancetype)init {
   // Copy defaults.
   webrtc::PeerConnectionInterface::RTCConfiguration config;
+  config.sdp_semantics = webrtc::SdpSemantics::kPlanB_DEPRECATED;
   return [self initWithNativeConfiguration:config];
 }
 
@@ -532,6 +534,9 @@
       return RTCSdpSemanticsPlanB;
     case webrtc::SdpSemantics::kUnifiedPlan:
       return RTCSdpSemanticsUnifiedPlan;
+    case webrtc::SdpSemantics::kNotSpecified:
+      RTC_DCHECK_NOTREACHED();
+      return RTCSdpSemanticsUnifiedPlan;
   }
 }