diff --git a/api/candidate.cc b/api/candidate.cc
index 128c470e2f..c2c6c53017 100644
--- a/api/candidate.cc
+++ b/api/candidate.cc
@@ -78,7 +78,7 @@ std::string Candidate::ToStringInternal(bool sensitive) const {
       << ":" << related_address_.ToString() << ":" << username_ << ":"
       << password_ << ":" << network_id_ << ":" << network_cost_ << ":"
       << generation_ << "]";
-  return ost.str();
+  return ost.Release();
 }
 
 uint32_t Candidate::GetPriority(uint32_t type_preference,
diff --git a/api/test/videocodec_test_stats.cc b/api/test/videocodec_test_stats.cc
index 78c39d0a54..8a935f3d96 100644
--- a/api/test/videocodec_test_stats.cc
+++ b/api/test/videocodec_test_stats.cc
@@ -36,7 +36,7 @@ std::string VideoCodecTestStats::FrameStatistics::ToString() const {
   ss << " decode_time_us " << decode_time_us;
   ss << " rtp_timestamp " << rtp_timestamp;
   ss << " target_bitrate_kbps " << target_bitrate_kbps;
-  return ss.str();
+  return ss.Release();
 }
 
 VideoCodecTestStats::VideoStatistics::VideoStatistics() = default;
@@ -83,7 +83,7 @@ std::string VideoCodecTestStats::VideoStatistics::ToString(
   ss << "\n" << prefix << "num_key_frames: " << num_key_frames;
   ss << "\n" << prefix << "num_spatial_resizes: " << num_spatial_resizes;
   ss << "\n" << prefix << "max_nalu_size_bytes: " << max_nalu_size_bytes;
-  return ss.str();
+  return ss.Release();
 }
 
 VideoCodecTestStats::FrameStatistics::FrameStatistics(size_t frame_number,
diff --git a/media/base/mediachannel.h b/media/base/mediachannel.h
index c1cc156d27..c7d8580dbc 100644
--- a/media/base/mediachannel.h
+++ b/media/base/mediachannel.h
@@ -88,7 +88,7 @@ static std::string VectorToString(const std::vector<T>& vals) {
     ost << vals[i].ToString();
   }
   ost << "]";
-  return ost.str();
+  return ost.Release();
 }
 
 // Options that can be applied to a VideoMediaChannel or a VideoMediaEngine.
@@ -120,7 +120,7 @@ struct VideoOptions {
                          screencast_min_bitrate_kbps);
     ost << ToStringIfSet("is_screencast ", is_screencast);
     ost << "}";
-    return ost.str();
+    return ost.Release();
   }
 
   // Enable denoising? This flag comes from the getUserMedia
@@ -157,7 +157,7 @@ struct RtpHeaderExtension {
     ost << "uri: " << uri;
     ost << ", id: " << id;
     ost << "}";
-    return ost.str();
+    return ost.Release();
   }
 
   std::string uri;
@@ -626,7 +626,7 @@ struct RtpParameters {
       separator = ", ";
     }
     ost << "}";
-    return ost.str();
+    return ost.Release();
   }
 
  protected:
diff --git a/media/engine/webrtcvideoengine.cc b/media/engine/webrtcvideoengine.cc
index 7caf3a4f56..29b0eb9194 100644
--- a/media/engine/webrtcvideoengine.cc
+++ b/media/engine/webrtcvideoengine.cc
@@ -190,7 +190,7 @@ static std::string CodecVectorToString(const std::vector<VideoCodec>& codecs) {
     }
   }
   out << "}";
-  return out.str();
+  return out.Release();
 }
 
 static bool ValidateCodecFormats(const std::vector<VideoCodec>& codecs) {
@@ -962,7 +962,7 @@ std::string WebRtcVideoChannel::CodecSettingsVectorToString(
     }
   }
   out << "}";
-  return out.str();
+  return out.Release();
 }
 
 bool WebRtcVideoChannel::GetSendCodec(VideoCodec* codec) {
diff --git a/media/engine/webrtcvoiceengine.cc b/media/engine/webrtcvoiceengine.cc
index d6c2967402..b8ccfc672e 100644
--- a/media/engine/webrtcvoiceengine.cc
+++ b/media/engine/webrtcvoiceengine.cc
@@ -106,7 +106,7 @@ std::string ToString(const AudioCodec& codec) {
     ss << " }";
   }
   ss << " (" << codec.id << ")";
-  return ss.str();
+  return ss.Release();
 }
 
 bool IsCodec(const AudioCodec& codec, const char* ref_name) {
diff --git a/modules/audio_coding/neteq/tools/neteq_input.cc b/modules/audio_coding/neteq/tools/neteq_input.cc
index ecbd9e054d..645894da6b 100644
--- a/modules/audio_coding/neteq/tools/neteq_input.cc
+++ b/modules/audio_coding/neteq/tools/neteq_input.cc
@@ -28,7 +28,7 @@ std::string NetEqInput::PacketData::ToString() const {
      << "ts: " << header.timestamp << ", "
      << "ssrc: " << header.ssrc << "}, "
      << "payload bytes: " << payload.size() << "}";
-  return ss.str();
+  return ss.Release();
 }
 
 TimeLimitedNetEqInput::TimeLimitedNetEqInput(std::unique_ptr<NetEqInput> input,
diff --git a/modules/audio_mixer/audio_mixer_impl_unittest.cc b/modules/audio_mixer/audio_mixer_impl_unittest.cc
index 86a4b66293..29632ca6b4 100644
--- a/modules/audio_mixer/audio_mixer_impl_unittest.cc
+++ b/modules/audio_mixer/audio_mixer_impl_unittest.cc
@@ -54,7 +54,7 @@ std::string ProduceDebugText(int sample_rate_hz,
   ss << "Sample rate: " << sample_rate_hz << " ";
   ss << "Number of channels: " << number_of_channels << " ";
   ss << "Number of sources: " << number_of_sources;
-  return ss.str();
+  return ss.Release();
 }
 
 AudioFrame frame_for_mixing;
diff --git a/modules/audio_mixer/audio_mixer_test.cc b/modules/audio_mixer/audio_mixer_test.cc
index 21b92daa1f..2004aeef46 100644
--- a/modules/audio_mixer/audio_mixer_test.cc
+++ b/modules/audio_mixer/audio_mixer_test.cc
@@ -78,7 +78,7 @@ class FilePlayingSource : public AudioMixer::Source {
     rtc::StringBuilder ss;
     ss << "{rate: " << sample_rate_hz_ << ", channels: " << number_of_channels_
        << ", samples_tot: " << wav_reader_->num_samples() << "}";
-    return ss.str();
+    return ss.Release();
   }
 
  private:
diff --git a/modules/audio_mixer/frame_combiner_unittest.cc b/modules/audio_mixer/frame_combiner_unittest.cc
index bf136295df..45d8a4e912 100644
--- a/modules/audio_mixer/frame_combiner_unittest.cc
+++ b/modules/audio_mixer/frame_combiner_unittest.cc
@@ -38,7 +38,7 @@ std::string ProduceDebugText(int sample_rate_hz,
   ss << "Sample rate: " << sample_rate_hz << " ,";
   ss << "number of channels: " << number_of_channels << " ,";
   ss << "number of sources: " << number_of_sources;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string ProduceDebugText(const FrameCombinerConfig& config) {
@@ -47,7 +47,7 @@ std::string ProduceDebugText(const FrameCombinerConfig& config) {
   ss << "number of channels: " << config.number_of_channels << " ,";
   ss << "limiter active: " << (config.use_limiter ? "on" : "off") << " ,";
   ss << "wave frequency: " << config.wave_frequency << " ,";
-  return ss.str();
+  return ss.Release();
 }
 
 AudioFrame frame1;
diff --git a/modules/audio_processing/aec3/adaptive_fir_filter_unittest.cc b/modules/audio_processing/aec3/adaptive_fir_filter_unittest.cc
index 7169965d53..3d583e861c 100644
--- a/modules/audio_processing/aec3/adaptive_fir_filter_unittest.cc
+++ b/modules/audio_processing/aec3/adaptive_fir_filter_unittest.cc
@@ -43,7 +43,7 @@ namespace {
 std::string ProduceDebugText(size_t delay) {
   rtc::StringBuilder ss;
   ss << ", Delay: " << delay;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/block_framer_unittest.cc b/modules/audio_processing/aec3/block_framer_unittest.cc
index 3f4122ffc9..9baade98d4 100644
--- a/modules/audio_processing/aec3/block_framer_unittest.cc
+++ b/modules/audio_processing/aec3/block_framer_unittest.cc
@@ -161,7 +161,7 @@ void RunWronglyInsertOrderTest(int sample_rate_hz,
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/block_processor_unittest.cc b/modules/audio_processing/aec3/block_processor_unittest.cc
index fbe1973f4c..71457868b2 100644
--- a/modules/audio_processing/aec3/block_processor_unittest.cc
+++ b/modules/audio_processing/aec3/block_processor_unittest.cc
@@ -95,7 +95,7 @@ void RunCaptureNumBandsVerificationTest(int sample_rate_hz) {
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/decimator_unittest.cc b/modules/audio_processing/aec3/decimator_unittest.cc
index 0c230d0529..08dc428666 100644
--- a/modules/audio_processing/aec3/decimator_unittest.cc
+++ b/modules/audio_processing/aec3/decimator_unittest.cc
@@ -28,7 +28,7 @@ namespace {
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 constexpr size_t kDownSamplingFactors[] = {2, 4, 8};
diff --git a/modules/audio_processing/aec3/echo_canceller3_unittest.cc b/modules/audio_processing/aec3/echo_canceller3_unittest.cc
index 8cc6d5be55..3f1e059a0c 100644
--- a/modules/audio_processing/aec3/echo_canceller3_unittest.cc
+++ b/modules/audio_processing/aec3/echo_canceller3_unittest.cc
@@ -606,13 +606,13 @@ class EchoCanceller3Tester {
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string ProduceDebugText(int sample_rate_hz, int variant) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz << ", variant: " << variant;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc b/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc
index 5764d1c43d..311a4a22d5 100644
--- a/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc
+++ b/modules/audio_processing/aec3/echo_path_delay_estimator_unittest.cc
@@ -29,7 +29,7 @@ std::string ProduceDebugText(size_t delay, size_t down_sampling_factor) {
   rtc::StringBuilder ss;
   ss << "Delay: " << delay;
   ss << ", Down sampling factor: " << down_sampling_factor;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/echo_remover_unittest.cc b/modules/audio_processing/aec3/echo_remover_unittest.cc
index 9a246ede30..da03f4c8e8 100644
--- a/modules/audio_processing/aec3/echo_remover_unittest.cc
+++ b/modules/audio_processing/aec3/echo_remover_unittest.cc
@@ -30,13 +30,13 @@ namespace {
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string ProduceDebugText(int sample_rate_hz, int delay) {
   rtc::StringBuilder ss(ProduceDebugText(sample_rate_hz));
   ss << ", Delay: " << delay;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/frame_blocker_unittest.cc b/modules/audio_processing/aec3/frame_blocker_unittest.cc
index 1fb7601e38..3ec74cc093 100644
--- a/modules/audio_processing/aec3/frame_blocker_unittest.cc
+++ b/modules/audio_processing/aec3/frame_blocker_unittest.cc
@@ -230,7 +230,7 @@ void RunWrongExtractOrderTest(int sample_rate_hz,
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/main_filter_update_gain_unittest.cc b/modules/audio_processing/aec3/main_filter_update_gain_unittest.cc
index 6dbf69f591..8c44ae064e 100644
--- a/modules/audio_processing/aec3/main_filter_update_gain_unittest.cc
+++ b/modules/audio_processing/aec3/main_filter_update_gain_unittest.cc
@@ -177,14 +177,14 @@ void RunFilterUpdateTest(int num_blocks_to_process,
 std::string ProduceDebugText(int filter_length_blocks) {
   rtc::StringBuilder ss;
   ss << "Length: " << filter_length_blocks;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string ProduceDebugText(size_t delay, int filter_length_blocks) {
   rtc::StringBuilder ss;
   ss << "Delay: " << delay << ", ";
   ss << ProduceDebugText(filter_length_blocks);
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/matched_filter_unittest.cc b/modules/audio_processing/aec3/matched_filter_unittest.cc
index 4353003a87..16b603a13f 100644
--- a/modules/audio_processing/aec3/matched_filter_unittest.cc
+++ b/modules/audio_processing/aec3/matched_filter_unittest.cc
@@ -37,7 +37,7 @@ std::string ProduceDebugText(size_t delay, size_t down_sampling_factor) {
   rtc::StringBuilder ss;
   ss << "Delay: " << delay;
   ss << ", Down sampling factor: " << down_sampling_factor;
-  return ss.str();
+  return ss.Release();
 }
 
 constexpr size_t kNumMatchedFilters = 10;
diff --git a/modules/audio_processing/aec3/render_delay_buffer_unittest.cc b/modules/audio_processing/aec3/render_delay_buffer_unittest.cc
index 29df28cca6..ee89597261 100644
--- a/modules/audio_processing/aec3/render_delay_buffer_unittest.cc
+++ b/modules/audio_processing/aec3/render_delay_buffer_unittest.cc
@@ -27,7 +27,7 @@ namespace {
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/render_delay_controller_unittest.cc b/modules/audio_processing/aec3/render_delay_controller_unittest.cc
index 4486d1beb5..93c64998e9 100644
--- a/modules/audio_processing/aec3/render_delay_controller_unittest.cc
+++ b/modules/audio_processing/aec3/render_delay_controller_unittest.cc
@@ -31,13 +31,13 @@ namespace {
 std::string ProduceDebugText(int sample_rate_hz) {
   rtc::StringBuilder ss;
   ss << "Sample rate: " << sample_rate_hz;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string ProduceDebugText(int sample_rate_hz, size_t delay) {
   rtc::StringBuilder ss;
   ss << ProduceDebugText(sample_rate_hz) << ", Delay: " << delay;
-  return ss.str();
+  return ss.Release();
 }
 
 constexpr size_t kDownSamplingFactors[] = {2, 4, 8};
diff --git a/modules/audio_processing/aec3/shadow_filter_update_gain_unittest.cc b/modules/audio_processing/aec3/shadow_filter_update_gain_unittest.cc
index d363689ac7..c040bbff91 100644
--- a/modules/audio_processing/aec3/shadow_filter_update_gain_unittest.cc
+++ b/modules/audio_processing/aec3/shadow_filter_update_gain_unittest.cc
@@ -118,14 +118,14 @@ void RunFilterUpdateTest(int num_blocks_to_process,
 std::string ProduceDebugText(int filter_length_blocks) {
   rtc::StringBuilder ss;
   ss << "Length: " << filter_length_blocks;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string ProduceDebugText(size_t delay, int filter_length_blocks) {
   rtc::StringBuilder ss;
   ss << "Delay: " << delay << ", ";
   ss << ProduceDebugText(filter_length_blocks);
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/aec3/subtractor_unittest.cc b/modules/audio_processing/aec3/subtractor_unittest.cc
index b308d38f95..ba744a6a83 100644
--- a/modules/audio_processing/aec3/subtractor_unittest.cc
+++ b/modules/audio_processing/aec3/subtractor_unittest.cc
@@ -106,7 +106,7 @@ std::string ProduceDebugText(size_t delay, int filter_length_blocks) {
   rtc::StringBuilder ss;
   ss << "Delay: " << delay << ", ";
   ss << "Length: " << filter_length_blocks;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/audio_processing/gain_controller2.cc b/modules/audio_processing/gain_controller2.cc
index 6368e92dd7..4d7cc1cd05 100644
--- a/modules/audio_processing/gain_controller2.cc
+++ b/modules/audio_processing/gain_controller2.cc
@@ -73,7 +73,7 @@ std::string GainController2::ToString(
   rtc::StringBuilder ss;
   ss << "{enabled: " << (config.enabled ? "true" : "false") << ", "
      << "fixed_gain_dB: " << config.fixed_gain_db << "}";
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace webrtc
diff --git a/modules/audio_processing/test/audio_processing_simulator.cc b/modules/audio_processing/test/audio_processing_simulator.cc
index e8519f24bf..4ac92ee796 100644
--- a/modules/audio_processing/test/audio_processing_simulator.cc
+++ b/modules/audio_processing/test/audio_processing_simulator.cc
@@ -644,7 +644,7 @@ std::string GetIndexedOutputWavFilename(const std::string& wav_name,
   rtc::StringBuilder ss;
   ss << wav_name.substr(0, wav_name.size() - 4) << "_" << counter
      << wav_name.substr(wav_name.size() - 4);
-  return ss.str();
+  return ss.Release();
 }
 
 void WriteEchoLikelihoodGraphFileHeader(std::ofstream* output_file) {
diff --git a/modules/audio_processing/test/fake_recording_device_unittest.cc b/modules/audio_processing/test/fake_recording_device_unittest.cc
index 484972ccc5..a14da827c5 100644
--- a/modules/audio_processing/test/fake_recording_device_unittest.cc
+++ b/modules/audio_processing/test/fake_recording_device_unittest.cc
@@ -100,13 +100,13 @@ void CheckSameSign(const ChannelBuffer<float>* src,
 std::string FakeRecordingDeviceKindToString(int fake_rec_device_kind) {
   rtc::StringBuilder ss;
   ss << "fake recording device: " << fake_rec_device_kind;
-  return ss.str();
+  return ss.Release();
 }
 
 std::string AnalogLevelToString(int level) {
   rtc::StringBuilder ss;
   ss << "analog level: " << level;
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace
diff --git a/modules/remote_bitrate_estimator/test/bwe_test_framework.h b/modules/remote_bitrate_estimator/test/bwe_test_framework.h
index 6c4a1ec21e..c84a90187c 100644
--- a/modules/remote_bitrate_estimator/test/bwe_test_framework.h
+++ b/modules/remote_bitrate_estimator/test/bwe_test_framework.h
@@ -131,7 +131,7 @@ class Stats {
     rtc::StringBuilder ss;
     ss << (GetMean() >= 0 ? GetMean() : -1) << ", "
        << (GetStdDev() >= 0 ? GetStdDev() : -1);
-    return ss.str();
+    return ss.Release();
   }
 
   void Log(const std::string& units) {
diff --git a/modules/remote_bitrate_estimator/test/bwe_test_logging.cc b/modules/remote_bitrate_estimator/test/bwe_test_logging.cc
index 0778040eb0..cf44fa070a 100644
--- a/modules/remote_bitrate_estimator/test/bwe_test_logging.cc
+++ b/modules/remote_bitrate_estimator/test/bwe_test_logging.cc
@@ -29,7 +29,7 @@ namespace bwe {
 static std::string ToString(uint32_t v) {
   rtc::StringBuilder ss;
   ss << v;
-  return ss.str();
+  return ss.Release();
 }
 
 Logging::ThreadState::ThreadState() = default;
diff --git a/modules/video_coding/codecs/test/videocodec_test_fixture_impl.cc b/modules/video_coding/codecs/test/videocodec_test_fixture_impl.cc
index 2251df793c..4dc268a043 100644
--- a/modules/video_coding/codecs/test/videocodec_test_fixture_impl.cc
+++ b/modules/video_coding/codecs/test/videocodec_test_fixture_impl.cc
@@ -279,7 +279,7 @@ std::string VideoCodecTestFixtureImpl::Config::ToString() const {
     }
   }
   ss << "\n";
-  return ss.str();
+  return ss.Release();
 }
 
 std::string VideoCodecTestFixtureImpl::Config::CodecName() const {
diff --git a/p2p/base/dtlstransport.h b/p2p/base/dtlstransport.h
index 5c0f795a08..456f375a10 100644
--- a/p2p/base/dtlstransport.h
+++ b/p2p/base/dtlstransport.h
@@ -186,7 +186,7 @@ class DtlsTransport : public DtlsTransportInternal {
     rtc::StringBuilder sb;
     sb << "DtlsTransport[" << transport_name_ << "|" << component_ << "|"
        << RECEIVING_ABBREV[receiving()] << WRITABLE_ABBREV[writable()] << "]";
-    return sb.str();
+    return sb.Release();
   }
 
  private:
diff --git a/p2p/base/p2ptransportchannel.h b/p2p/base/p2ptransportchannel.h
index e4d371f2df..fbed344cc3 100644
--- a/p2p/base/p2ptransportchannel.h
+++ b/p2p/base/p2ptransportchannel.h
@@ -177,7 +177,7 @@ class P2PTransportChannel : public IceTransportInternal {
     rtc::StringBuilder ss;
     ss << "Channel[" << transport_name_ << "|" << component_ << "|"
        << RECEIVING_ABBREV[receiving_] << WRITABLE_ABBREV[writable_] << "]";
-    return ss.str();
+    return ss.Release();
   }
 
  private:
diff --git a/p2p/base/port.cc b/p2p/base/port.cc
index 473f623a29..095b3a6d02 100644
--- a/p2p/base/port.cc
+++ b/p2p/base/port.cc
@@ -909,7 +909,7 @@ std::string Port::ToString() const {
   ss << "Port[" << rtc::ToHex(reinterpret_cast<uintptr_t>(this)) << ":"
      << content_name_ << ":" << component_ << ":" << generation_ << ":" << type_
      << ":" << network_->ToString() << "]";
-  return ss.str();
+  return ss.Release();
 }
 
 // TODO(honghaiz): Make the network cost configurable from user setting.
@@ -1612,7 +1612,7 @@ std::string Connection::ToString() const {
   } else {
     ss << "-]";
   }
-  return ss.str();
+  return ss.Release();
 }
 
 std::string Connection::ToSensitiveString() const {
diff --git a/p2p/base/turnport.cc b/p2p/base/turnport.cc
index 0883534538..a6d25512b4 100644
--- a/p2p/base/turnport.cc
+++ b/p2p/base/turnport.cc
@@ -1240,7 +1240,7 @@ std::string TurnPort::ReconstructedServerUrl() {
   rtc::StringBuilder url;
   url << scheme << ":" << server_address_.address.ipaddr().ToString() << ":"
       << server_address_.address.port() << "?transport=" << transport;
-  return url.str();
+  return url.Release();
 }
 
 void TurnPort::TurnCustomizerMaybeModifyOutgoingStunMessage(
diff --git a/p2p/base/turnserver.cc b/p2p/base/turnserver.cc
index 160e25965d..022113e7e7 100644
--- a/p2p/base/turnserver.cc
+++ b/p2p/base/turnserver.cc
@@ -600,7 +600,7 @@ std::string TurnServerConnection::ToString() const {
   };
   rtc::StringBuilder ost;
   ost << src_.ToString() << "-" << dst_.ToString() << ":"<< kProtos[proto_];
-  return ost.str();
+  return ost.Release();
 }
 
 TurnServerAllocation::TurnServerAllocation(TurnServer* server,
@@ -633,7 +633,7 @@ TurnServerAllocation::~TurnServerAllocation() {
 std::string TurnServerAllocation::ToString() const {
   rtc::StringBuilder ost;
   ost << "Alloc[" << conn_.ToString() << "]";
-  return ost.str();
+  return ost.Release();
 }
 
 void TurnServerAllocation::HandleTurnMessage(const TurnMessage* msg) {
diff --git a/pc/mediasession_unittest.cc b/pc/mediasession_unittest.cc
index 1a33a7ca9e..db325ed2ef 100644
--- a/pc/mediasession_unittest.cc
+++ b/pc/mediasession_unittest.cc
@@ -3711,7 +3711,7 @@ void TestAudioCodecsAnswer(RtpTransceiverDirection offer_direction,
         first = false;
       }
       os << " }";
-      return os.str();
+      return os.Release();
     };
 
     EXPECT_TRUE(acd->codecs() == target_codecs)
diff --git a/pc/peerconnection.cc b/pc/peerconnection.cc
index 029d77939c..7ad2e3d973 100644
--- a/pc/peerconnection.cc
+++ b/pc/peerconnection.cc
@@ -607,7 +607,7 @@ std::string GetSetDescriptionErrorMessage(cricket::ContentSource source,
   rtc::StringBuilder oss;
   oss << "Failed to set " << (source == cricket::CS_LOCAL ? "local" : "remote")
       << " " << SdpTypeToString(type) << " sdp: " << error.message();
-  return oss.str();
+  return oss.Release();
 }
 
 std::string GetStreamIdsString(rtc::ArrayView<const std::string> stream_ids) {
@@ -5847,7 +5847,7 @@ std::string PeerConnection::GetSessionErrorMsg() {
   rtc::StringBuilder desc;
   desc << kSessionError << SessionErrorToString(session_error()) << ". ";
   desc << kSessionErrorDesc << session_error_desc() << ".";
-  return desc.str();
+  return desc.Release();
 }
 
 void PeerConnection::ReportSdpFormatReceived(
diff --git a/rtc_base/network.cc b/rtc_base/network.cc
index f0d402efe6..67888ede83 100644
--- a/rtc_base/network.cc
+++ b/rtc_base/network.cc
@@ -184,7 +184,7 @@ std::string MakeNetworkKey(const std::string& name,
                            int prefix_length) {
   rtc::StringBuilder ost;
   ost << name << "%" << prefix.ToString() << "/" << prefix_length;
-  return ost.str();
+  return ost.Release();
 }
 // Test if the network name matches the type<number> pattern, e.g. eth0. The
 // matching is case-sensitive.
@@ -1075,7 +1075,7 @@ std::string Network::ToString() const {
     ss << "/" << AdapterTypeToString(underlying_type_for_vpn_);
   }
   ss << ":id=" << id_ << "]";
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace rtc
diff --git a/rtc_base/sslidentity.cc b/rtc_base/sslidentity.cc
index b9ada0074d..823fc388a3 100644
--- a/rtc_base/sslidentity.cc
+++ b/rtc_base/sslidentity.cc
@@ -136,7 +136,7 @@ std::string SSLIdentity::DerToPem(const std::string& pem_type,
 
   result << "-----END " << pem_type << "-----\n";
 
-  return result.str();
+  return result.Release();
 }
 
 // static
diff --git a/rtc_base/strings/string_builder.h b/rtc_base/strings/string_builder.h
index d95b29decb..186c2f7b9d 100644
--- a/rtc_base/strings/string_builder.h
+++ b/rtc_base/strings/string_builder.h
@@ -157,8 +157,8 @@ class StringBuilder {
   size_t size() const { return str_.size(); }
 
   std::string Release() {
-    std::string ret;
-    std::swap(str_, ret);
+    std::string ret = std::move(str_);
+    str_.clear();
     return ret;
   }
 
diff --git a/rtc_base/timeutils.h b/rtc_base/timeutils.h
index c6ea0127d7..3a412a47cf 100644
--- a/rtc_base/timeutils.h
+++ b/rtc_base/timeutils.h
@@ -145,7 +145,7 @@ class IntervalRange {
   std::string ToString() const {
     rtc::StringBuilder ss;
     ss << "[" << min_ << "," << max_ << "]";
-    return ss.str();
+    return ss.Release();
   }
 
   bool operator==(const IntervalRange& o) const {
diff --git a/rtc_tools/event_log_visualizer/analyzer.cc b/rtc_tools/event_log_visualizer/analyzer.cc
index c51aae3ab5..c9187ca70c 100644
--- a/rtc_tools/event_log_visualizer/analyzer.cc
+++ b/rtc_tools/event_log_visualizer/analyzer.cc
@@ -78,7 +78,7 @@ void SortPacketFeedbackVector(std::vector<PacketFeedback>* vec) {
 std::string SsrcToString(uint32_t ssrc) {
   rtc::StringBuilder ss;
   ss << "SSRC " << ssrc;
-  return ss.str();
+  return ss.Release();
 }
 
 // Checks whether an SSRC is contained in the list of desired SSRCs.
@@ -424,7 +424,7 @@ std::string GetCandidatePairLogDescriptionAsString(
      << remote_candidate_type << ":"
      << GetAddressFamilyAsString(config.remote_address_family) << "@"
      << GetProtocolAsString(config.candidate_pair_protocol);
-  return ss.str();
+  return ss.Release();
 }
 
 std::string GetDirectionAsString(PacketDirection direction) {
diff --git a/sdk/android/src/jni/androidnetworkmonitor.cc b/sdk/android/src/jni/androidnetworkmonitor.cc
index 3dd280b7d7..b1351ef1e1 100644
--- a/sdk/android/src/jni/androidnetworkmonitor.cc
+++ b/sdk/android/src/jni/androidnetworkmonitor.cc
@@ -164,7 +164,7 @@ std::string NetworkInformation::ToString() const {
     ss << " " << address.ToString();
   }
   ss << "]";
-  return ss.str();
+  return ss.Release();
 }
 
 AndroidNetworkMonitor::AndroidNetworkMonitor(
diff --git a/video/end_to_end_tests/stats_tests.cc b/video/end_to_end_tests/stats_tests.cc
index 7899eb7de6..db500492a7 100644
--- a/video/end_to_end_tests/stats_tests.cc
+++ b/video/end_to_end_tests/stats_tests.cc
@@ -218,7 +218,7 @@ TEST_F(StatsEndToEndTest, GetStats) {
     std::string CompoundKey(const char* name, uint32_t ssrc) {
       rtc::StringBuilder oss;
       oss << name << "_" << ssrc;
-      return oss.str();
+      return oss.Release();
     }
 
     bool AllStatsFilled(const std::map<std::string, bool>& stats_map) {
diff --git a/video/stats_counter.cc b/video/stats_counter.cc
index 8f282b0ae9..1e72a79bbd 100644
--- a/video/stats_counter.cc
+++ b/video/stats_counter.cc
@@ -36,7 +36,7 @@ std::string AggregatedStats::ToStringWithMultiplier(int multiplier) const {
   ss << "min:" << (min * multiplier) << ", ";
   ss << "avg:" << (average * multiplier) << ", ";
   ss << "max:" << (max * multiplier) << "}";
-  return ss.str();
+  return ss.Release();
 }
 
 // Class holding periodically computed metrics.
diff --git a/video/video_quality_test.cc b/video/video_quality_test.cc
index 9596cfa4ba..7f7c8737a1 100644
--- a/video/video_quality_test.cc
+++ b/video/video_quality_test.cc
@@ -250,7 +250,7 @@ std::string VideoQualityTest::GenerateGraphTitle() const {
   if (params_.ss[0].num_spatial_layers > 1)
     ss << ", Layer #" << params_.ss[0].selected_sl;
   ss << ")";
-  return ss.str();
+  return ss.Release();
 }
 
 void VideoQualityTest::CheckParamsAndInjectionComponents() {
diff --git a/video/video_stream_encoder.cc b/video/video_stream_encoder.cc
index 0bcf8ca28b..b7b5a32611 100644
--- a/video/video_stream_encoder.cc
+++ b/video/video_stream_encoder.cc
@@ -1267,7 +1267,7 @@ std::string VideoStreamEncoder::AdaptCounter::ToString() const {
   rtc::StringBuilder ss;
   ss << "Downgrade counts: fps: {" << ToString(fps_counters_);
   ss << "}, resolution: {" << ToString(resolution_counters_) << "}";
-  return ss.str();
+  return ss.Release();
 }
 
 VideoStreamEncoderObserver::AdaptationSteps
@@ -1361,7 +1361,7 @@ std::string VideoStreamEncoder::AdaptCounter::ToString(
   for (size_t reason = 0; reason < kScaleReasonSize; ++reason) {
     ss << (reason ? " cpu" : "quality") << ":" << counters[reason];
   }
-  return ss.str();
+  return ss.Release();
 }
 
 }  // namespace webrtc