diff --git a/modules/rtp_rtcp/BUILD.gn b/modules/rtp_rtcp/BUILD.gn
index 6ade021..286f1e0 100644
--- a/modules/rtp_rtcp/BUILD.gn
+++ b/modules/rtp_rtcp/BUILD.gn
@@ -88,7 +88,6 @@
     "../../:typedefs",
     "../../api:array_view",
     "../../api:libjingle_peerconnection_api",
-    "../../api:optional",
     "../../api/audio_codecs:audio_codecs_api",
     "../../api/video:video_frame",
     "../../common_video",
@@ -96,6 +95,7 @@
     "../../rtc_base:deprecation",
     "../../rtc_base:rtc_base_approved",
     "../../system_wrappers",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 }
 
@@ -196,7 +196,6 @@
     "../../:typedefs",
     "../../api:array_view",
     "../../api:libjingle_peerconnection_api",
-    "../../api:optional",
     "../../api:transport_api",
     "../../api/audio_codecs:audio_codecs_api",
     "../../api/video:video_bitrate_allocation",
@@ -221,6 +220,7 @@
     "../../system_wrappers:metrics_api",
     "../audio_coding:audio_format_conversion",
     "../remote_bitrate_estimator",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 
   # TODO(jschuh): Bug 1348: fix this warning.
@@ -245,7 +245,6 @@
     "../../:webrtc_common",
     "../../api:array_view",
     "../../api:libjingle_peerconnection_api",
-    "../../api:optional",
     "../../api:transport_api",
     "../../api/video:video_bitrate_allocation",
     "../../rtc_base:checks",
@@ -253,6 +252,7 @@
     "../../rtc_base:rtc_task_queue",
     "../../rtc_base:weak_ptr",
     "../../system_wrappers",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 }
 
@@ -292,11 +292,11 @@
     ":rtp_rtcp",
     ":rtp_rtcp_format",
     "..:module_api",
-    "../../api:optional",
     "../../api/video:video_bitrate_allocation",
     "../../rtc_base:checks",
     "../../rtc_base:rtc_base_approved",
     "../../test:test_support",
+    "//third_party/abseil-cpp/absl/types:optional",
   ]
 }
 
@@ -410,7 +410,6 @@
       "../../:typedefs",
       "../../api:array_view",
       "../../api:libjingle_peerconnection_api",
-      "../../api:optional",
       "../../api:transport_api",
       "../../api/video:video_bitrate_allocation",
       "../../api/video:video_frame",
@@ -430,6 +429,7 @@
       "../../test:test_common",
       "../../test:test_support",
       "../audio_coding:audio_format_conversion",
+      "//third_party/abseil-cpp/absl/types:optional",
     ]
 
     # TODO(jschuh): bugs.webrtc.org/1348: fix this warning.
diff --git a/modules/rtp_rtcp/include/rtp_payload_registry.h b/modules/rtp_rtcp/include/rtp_payload_registry.h
index dcaa2a2..c80f475 100644
--- a/modules/rtp_rtcp/include/rtp_payload_registry.h
+++ b/modules/rtp_rtcp/include/rtp_payload_registry.h
@@ -14,8 +14,8 @@
 #include <map>
 #include <set>
 
+#include "absl/types/optional.h"
 #include "api/audio_codecs/audio_format.h"
-#include "api/optional.h"
 #include "api/video_codecs/video_codec.h"
 #include "modules/rtp_rtcp/source/rtp_utility.h"
 #include "rtc_base/criticalsection.h"
@@ -42,7 +42,7 @@
 
   int GetPayloadTypeFrequency(uint8_t payload_type) const;
 
-  rtc::Optional<RtpUtility::Payload> PayloadTypeToPayload(
+  absl::optional<RtpUtility::Payload> PayloadTypeToPayload(
       uint8_t payload_type) const;
 
   void ResetLastReceivedPayloadTypes() {
diff --git a/modules/rtp_rtcp/include/rtp_rtcp.h b/modules/rtp_rtcp/include/rtp_rtcp.h
index 8ddcdb3..773075e 100644
--- a/modules/rtp_rtcp/include/rtp_rtcp.h
+++ b/modules/rtp_rtcp/include/rtp_rtcp.h
@@ -16,7 +16,7 @@
 #include <utility>
 #include <vector>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "api/video/video_bitrate_allocation.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "modules/include/module.h"
@@ -199,7 +199,7 @@
                                      int associated_payload_type) = 0;
 
   // Returns the FlexFEC SSRC, if there is one.
-  virtual rtc::Optional<uint32_t> FlexfecSsrc() const = 0;
+  virtual absl::optional<uint32_t> FlexfecSsrc() const = 0;
 
   // Sets sending status. Sends kRtcpByeCode when going from true to false.
   // Returns -1 on failure else 0.
diff --git a/modules/rtp_rtcp/include/rtp_rtcp_defines.h b/modules/rtp_rtcp/include/rtp_rtcp_defines.h
index 31b3451..2cd3c54 100644
--- a/modules/rtp_rtcp/include/rtp_rtcp_defines.h
+++ b/modules/rtp_rtcp/include/rtp_rtcp_defines.h
@@ -91,8 +91,8 @@
   }
 
  private:
-  rtc::Optional<AudioPayload> audio_payload_;
-  rtc::Optional<VideoPayload> video_payload_;
+  absl::optional<AudioPayload> audio_payload_;
+  absl::optional<VideoPayload> video_payload_;
 };
 
 enum RTPAliveType { kRtpDead = 0, kRtpNoRtp = 1, kRtpAlive = 2 };
diff --git a/modules/rtp_rtcp/mocks/mock_rtp_rtcp.h b/modules/rtp_rtcp/mocks/mock_rtp_rtcp.h
index db32a8c..d176930 100644
--- a/modules/rtp_rtcp/mocks/mock_rtp_rtcp.h
+++ b/modules/rtp_rtcp/mocks/mock_rtp_rtcp.h
@@ -16,7 +16,7 @@
 #include <utility>
 #include <vector>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "api/video/video_bitrate_allocation.h"
 #include "modules/include/module.h"
 #include "modules/rtp_rtcp/include/rtp_rtcp.h"
@@ -75,7 +75,7 @@
   MOCK_CONST_METHOD0(RtxSendStatus, int());
   MOCK_METHOD1(SetRtxSsrc, void(uint32_t));
   MOCK_METHOD2(SetRtxSendPayloadType, void(int, int));
-  MOCK_CONST_METHOD0(FlexfecSsrc, rtc::Optional<uint32_t>());
+  MOCK_CONST_METHOD0(FlexfecSsrc, absl::optional<uint32_t>());
   MOCK_CONST_METHOD0(RtxSendPayloadType, std::pair<int, int>());
   MOCK_METHOD1(SetSendingStatus, int32_t(bool sending));
   MOCK_CONST_METHOD0(Sending, bool());
diff --git a/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc b/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
index 664e02b..06472ef 100644
--- a/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
+++ b/modules/rtp_rtcp/source/rtcp_packet/extended_reports.cc
@@ -57,7 +57,7 @@
   rrtr_block_.reset();
   dlrr_block_.ClearItems();
   voip_metric_block_.reset();
-  target_bitrate_ = rtc::nullopt;
+  target_bitrate_ = absl::nullopt;
 
   const uint8_t* current_block = packet.payload() + kXrBaseLength;
   const uint8_t* const packet_end =
diff --git a/modules/rtp_rtcp/source/rtcp_packet/extended_reports.h b/modules/rtp_rtcp/source/rtcp_packet/extended_reports.h
index 91794f8..7855502 100644
--- a/modules/rtp_rtcp/source/rtcp_packet/extended_reports.h
+++ b/modules/rtp_rtcp/source/rtcp_packet/extended_reports.h
@@ -13,7 +13,7 @@
 
 #include <vector>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "modules/rtp_rtcp/source/rtcp_packet.h"
 #include "modules/rtp_rtcp/source/rtcp_packet/dlrr.h"
 #include "modules/rtp_rtcp/source/rtcp_packet/rrtr.h"
@@ -44,12 +44,12 @@
   void SetTargetBitrate(const TargetBitrate& target_bitrate);
 
   uint32_t sender_ssrc() const { return sender_ssrc_; }
-  const rtc::Optional<Rrtr>& rrtr() const { return rrtr_block_; }
+  const absl::optional<Rrtr>& rrtr() const { return rrtr_block_; }
   const Dlrr& dlrr() const { return dlrr_block_; }
-  const rtc::Optional<VoipMetric>& voip_metric() const {
+  const absl::optional<VoipMetric>& voip_metric() const {
     return voip_metric_block_;
   }
-  const rtc::Optional<TargetBitrate>& target_bitrate() const {
+  const absl::optional<TargetBitrate>& target_bitrate() const {
     return target_bitrate_;
   }
 
@@ -76,10 +76,10 @@
   void ParseTargetBitrateBlock(const uint8_t* block, uint16_t block_length);
 
   uint32_t sender_ssrc_;
-  rtc::Optional<Rrtr> rrtr_block_;
+  absl::optional<Rrtr> rrtr_block_;
   Dlrr dlrr_block_;  // Dlrr without items treated same as no dlrr block.
-  rtc::Optional<VoipMetric> voip_metric_block_;
-  rtc::Optional<TargetBitrate> target_bitrate_;
+  absl::optional<VoipMetric> voip_metric_block_;
+  absl::optional<TargetBitrate> target_bitrate_;
 };
 }  // namespace rtcp
 }  // namespace webrtc
diff --git a/modules/rtp_rtcp/source/rtcp_packet/target_bitrate_unittest.cc b/modules/rtp_rtcp/source/rtcp_packet/target_bitrate_unittest.cc
index 5fec75f..b16bb5b 100644
--- a/modules/rtp_rtcp/source/rtcp_packet/target_bitrate_unittest.cc
+++ b/modules/rtp_rtcp/source/rtcp_packet/target_bitrate_unittest.cc
@@ -67,7 +67,7 @@
   rtcp::ExtendedReports xr;
   EXPECT_TRUE(ParseSinglePacket(kRtcpPacket, &xr));
   EXPECT_EQ(kSsrc, xr.sender_ssrc());
-  const rtc::Optional<TargetBitrate>& target_bitrate = xr.target_bitrate();
+  const absl::optional<TargetBitrate>& target_bitrate = xr.target_bitrate();
   ASSERT_TRUE(static_cast<bool>(target_bitrate));
   CheckBitrateItems(target_bitrate->GetTargetBitrates());
 }
diff --git a/modules/rtp_rtcp/source/rtcp_receiver.cc b/modules/rtp_rtcp/source/rtcp_receiver.cc
index 618c533..af164cc 100644
--- a/modules/rtp_rtcp/source/rtcp_receiver.cc
+++ b/modules/rtp_rtcp/source/rtcp_receiver.cc
@@ -72,7 +72,7 @@
   int64_t rtt_ms = 0;
   uint32_t receiver_estimated_max_bitrate_bps = 0;
   std::unique_ptr<rtcp::TransportFeedback> transport_feedback;
-  rtc::Optional<VideoBitrateAllocation> target_bitrate_allocation;
+  absl::optional<VideoBitrateAllocation> target_bitrate_allocation;
 };
 
 // Structure for handing TMMBR and TMMBN rtcp messages (RFC5104, section 3.5.4).
diff --git a/modules/rtp_rtcp/source/rtcp_sender.h b/modules/rtp_rtcp/source/rtcp_sender.h
index 0452ec2..e274915 100644
--- a/modules/rtp_rtcp/source/rtcp_sender.h
+++ b/modules/rtp_rtcp/source/rtcp_sender.h
@@ -17,8 +17,8 @@
 #include <string>
 #include <vector>
 
+#include "absl/types/optional.h"
 #include "api/call/transport.h"
-#include "api/optional.h"
 #include "api/video/video_bitrate_allocation.h"
 #include "modules/remote_bitrate_estimator/include/bwe_defines.h"
 #include "modules/remote_bitrate_estimator/include/remote_bitrate_estimator.h"
@@ -237,7 +237,7 @@
       RTC_GUARDED_BY(critical_section_rtcp_sender_);
 
   // XR VoIP metric
-  rtc::Optional<RTCPVoIPMetric> xr_voip_metric_
+  absl::optional<RTCPVoIPMetric> xr_voip_metric_
       RTC_GUARDED_BY(critical_section_rtcp_sender_);
 
   RtcpPacketTypeCounterObserver* const packet_type_counter_observer_;
@@ -246,7 +246,7 @@
 
   RtcpNackStats nack_stats_ RTC_GUARDED_BY(critical_section_rtcp_sender_);
 
-  rtc::Optional<VideoBitrateAllocation> video_bitrate_allocation_
+  absl::optional<VideoBitrateAllocation> video_bitrate_allocation_
       RTC_GUARDED_BY(critical_section_rtcp_sender_);
 
   void SetFlag(uint32_t type, bool is_volatile)
diff --git a/modules/rtp_rtcp/source/rtcp_sender_unittest.cc b/modules/rtp_rtcp/source/rtcp_sender_unittest.cc
index f77c644..c7c38bf 100644
--- a/modules/rtp_rtcp/source/rtcp_sender_unittest.cc
+++ b/modules/rtp_rtcp/source/rtcp_sender_unittest.cc
@@ -679,7 +679,7 @@
   EXPECT_EQ(0, rtcp_sender_->SendRTCP(feedback_state(), kRtcpReport));
   EXPECT_EQ(1, parser()->xr()->num_packets());
   EXPECT_EQ(kSenderSsrc, parser()->xr()->sender_ssrc());
-  const rtc::Optional<rtcp::TargetBitrate>& target_bitrate =
+  const absl::optional<rtcp::TargetBitrate>& target_bitrate =
       parser()->xr()->target_bitrate();
   ASSERT_TRUE(target_bitrate);
   const std::vector<rtcp::TargetBitrate::BitrateItem>& bitrates =
diff --git a/modules/rtp_rtcp/source/rtcp_transceiver_impl.cc b/modules/rtp_rtcp/source/rtcp_transceiver_impl.cc
index 9716784..5cfe019 100644
--- a/modules/rtp_rtcp/source/rtcp_transceiver_impl.cc
+++ b/modules/rtp_rtcp/source/rtcp_transceiver_impl.cc
@@ -46,7 +46,7 @@
 
 struct RtcpTransceiverImpl::RemoteSenderState {
   uint8_t fir_sequence_number = 0;
-  rtc::Optional<SenderReportTimes> last_received_sender_report;
+  absl::optional<SenderReportTimes> last_received_sender_report;
   std::vector<MediaReceiverRtcpObserver*> observers;
 };
 
@@ -245,7 +245,7 @@
     return;
   RemoteSenderState& remote_sender =
       remote_senders_[sender_report.sender_ssrc()];
-  rtc::Optional<SenderReportTimes>& last =
+  absl::optional<SenderReportTimes>& last =
       remote_sender.last_received_sender_report;
   last.emplace();
   last->local_received_time_us = now_us;
diff --git a/modules/rtp_rtcp/source/rtcp_transceiver_impl.h b/modules/rtp_rtcp/source/rtcp_transceiver_impl.h
index 05c74f2..7bcd16f 100644
--- a/modules/rtp_rtcp/source/rtcp_transceiver_impl.h
+++ b/modules/rtp_rtcp/source/rtcp_transceiver_impl.h
@@ -16,8 +16,8 @@
 #include <string>
 #include <vector>
 
+#include "absl/types/optional.h"
 #include "api/array_view.h"
-#include "api/optional.h"
 #include "modules/rtp_rtcp/source/rtcp_packet/common_header.h"
 #include "modules/rtp_rtcp/source/rtcp_packet/dlrr.h"
 #include "modules/rtp_rtcp/source/rtcp_packet/remb.h"
@@ -91,7 +91,7 @@
   const RtcpTransceiverConfig config_;
 
   bool ready_to_send_;
-  rtc::Optional<rtcp::Remb> remb_;
+  absl::optional<rtcp::Remb> remb_;
   // TODO(danilchap): Remove entries from remote_senders_ that are no longer
   // needed.
   std::map<uint32_t, RemoteSenderState> remote_senders_;
diff --git a/modules/rtp_rtcp/source/rtcp_transceiver_impl_unittest.cc b/modules/rtp_rtcp/source/rtcp_transceiver_impl_unittest.cc
index df8178d..1fe5000 100644
--- a/modules/rtp_rtcp/source/rtcp_transceiver_impl_unittest.cc
+++ b/modules/rtp_rtcp/source/rtcp_transceiver_impl_unittest.cc
@@ -144,7 +144,7 @@
   config.outgoing_transport = &transport;
   config.initial_report_delay_ms = 10;
   config.task_queue = &queue;
-  rtc::Optional<RtcpTransceiverImpl> rtcp_transceiver;
+  absl::optional<RtcpTransceiverImpl> rtcp_transceiver;
 
   int64_t started_ms = rtc::TimeMillis();
   queue.PostTask([&] { rtcp_transceiver.emplace(config); });
@@ -169,7 +169,7 @@
   config.initial_report_delay_ms = 0;
   config.report_period_ms = kReportPeriodMs;
   config.task_queue = &queue;
-  rtc::Optional<RtcpTransceiverImpl> rtcp_transceiver;
+  absl::optional<RtcpTransceiverImpl> rtcp_transceiver;
   int64_t time_just_before_1st_packet_ms = 0;
   queue.PostTask([&] {
     // Because initial_report_delay_ms is set to 0, time_just_before_the_packet
@@ -202,7 +202,7 @@
   config.initial_report_delay_ms = 0;
   config.report_period_ms = kReportPeriodMs;
   config.task_queue = &queue;
-  rtc::Optional<RtcpTransceiverImpl> rtcp_transceiver;
+  absl::optional<RtcpTransceiverImpl> rtcp_transceiver;
   queue.PostTask([&] { rtcp_transceiver.emplace(config); });
 
   // Wait for first packet.
@@ -288,7 +288,7 @@
   config.initial_ready_to_send = false;
   config.outgoing_transport = &transport;
   config.task_queue = &queue;
-  rtc::Optional<RtcpTransceiverImpl> rtcp_transceiver;
+  absl::optional<RtcpTransceiverImpl> rtcp_transceiver;
   rtcp_transceiver.emplace(config);
 
   rtcp_transceiver->SetReadyToSend(true);
diff --git a/modules/rtp_rtcp/source/rtp_format_h264.cc b/modules/rtp_rtcp/source/rtp_format_h264.cc
index 0f46f9b..633f0ae 100644
--- a/modules/rtp_rtcp/source/rtp_format_h264.cc
+++ b/modules/rtp_rtcp/source/rtp_format_h264.cc
@@ -129,7 +129,7 @@
       // RtpDepacketizerH264::ParseSingleNalu (receive side, in orderer to
       // protect us from unknown or legacy send clients).
 
-      rtc::Optional<SpsParser::SpsState> sps;
+      absl::optional<SpsParser::SpsState> sps;
 
       std::unique_ptr<rtc::Buffer> output_buffer(new rtc::Buffer());
       // Add the type header to the output buffer first, so that the rewriter
@@ -514,7 +514,7 @@
         if (start_offset)
           output_buffer->AppendData(payload_data, start_offset);
 
-        rtc::Optional<SpsParser::SpsState> sps;
+        absl::optional<SpsParser::SpsState> sps;
 
         SpsVuiRewriter::ParseResult result = SpsVuiRewriter::ParseAndRewriteSps(
             &payload_data[start_offset], end_offset - start_offset, &sps,
@@ -596,7 +596,7 @@
         parsed_payload->frame_type = kVideoFrameKey;
         RTC_FALLTHROUGH();
       case H264::NaluType::kSlice: {
-        rtc::Optional<uint32_t> pps_id = PpsParser::ParsePpsIdFromSlice(
+        absl::optional<uint32_t> pps_id = PpsParser::ParsePpsIdFromSlice(
             &payload_data[start_offset], end_offset - start_offset);
         if (pps_id) {
           nalu.pps_id = *pps_id;
@@ -648,7 +648,7 @@
   if (first_fragment) {
     offset_ = 0;
     length_ -= kNalHeaderSize;
-    rtc::Optional<uint32_t> pps_id = PpsParser::ParsePpsIdFromSlice(
+    absl::optional<uint32_t> pps_id = PpsParser::ParsePpsIdFromSlice(
         payload_data + 2 * kNalHeaderSize, length_ - kNalHeaderSize);
     if (pps_id) {
       nalu.pps_id = *pps_id;
diff --git a/modules/rtp_rtcp/source/rtp_packet_history.cc b/modules/rtp_rtcp/source/rtp_packet_history.cc
index 2bd06c4..4fd384d 100644
--- a/modules/rtp_rtcp/source/rtp_packet_history.cc
+++ b/modules/rtp_rtcp/source/rtp_packet_history.cc
@@ -84,7 +84,7 @@
 
 void RtpPacketHistory::PutRtpPacket(std::unique_ptr<RtpPacketToSend> packet,
                                     StorageType type,
-                                    rtc::Optional<int64_t> send_time_ms) {
+                                    absl::optional<int64_t> send_time_ms) {
   RTC_DCHECK(packet);
   rtc::CritScope cs(&lock_);
   int64_t now_ms = clock_->TimeInMilliseconds();
@@ -146,21 +146,21 @@
   return rtc::MakeUnique<RtpPacketToSend>(*packet.packet);
 }
 
-rtc::Optional<RtpPacketHistory::PacketState> RtpPacketHistory::GetPacketState(
+absl::optional<RtpPacketHistory::PacketState> RtpPacketHistory::GetPacketState(
     uint16_t sequence_number,
     bool verify_rtt) const {
   rtc::CritScope cs(&lock_);
   if (mode_ == StorageMode::kDisabled) {
-    return rtc::nullopt;
+    return absl::nullopt;
   }
 
   auto rtp_it = packet_history_.find(sequence_number);
   if (rtp_it == packet_history_.end()) {
-    return rtc::nullopt;
+    return absl::nullopt;
   }
 
   if (verify_rtt && !VerifyRtt(rtp_it->second, clock_->TimeInMilliseconds())) {
-    return rtc::nullopt;
+    return absl::nullopt;
   }
 
   return StoredPacketToPacketState(rtp_it->second);
diff --git a/modules/rtp_rtcp/source/rtp_packet_history.h b/modules/rtp_rtcp/source/rtp_packet_history.h
index bfcdcc8..03527ff 100644
--- a/modules/rtp_rtcp/source/rtp_packet_history.h
+++ b/modules/rtp_rtcp/source/rtp_packet_history.h
@@ -42,7 +42,7 @@
     ~PacketState();
 
     uint16_t rtp_sequence_number = 0;
-    rtc::Optional<int64_t> send_time_ms;
+    absl::optional<int64_t> send_time_ms;
     int64_t capture_time_ms = 0;
     uint32_t ssrc = 0;
     size_t payload_size = 0;
@@ -74,7 +74,7 @@
   // be set accordingly.
   void PutRtpPacket(std::unique_ptr<RtpPacketToSend> packet,
                     StorageType type,
-                    rtc::Optional<int64_t> send_time_ms);
+                    absl::optional<int64_t> send_time_ms);
 
   // Gets stored RTP packet corresponding to the input |sequence number|.
   // Returns nullptr if packet is not found. If |verify_rtt| is true, doesn't
@@ -85,8 +85,8 @@
 
   // Similar to GetPacketAndSetSendTime(), but only returns a snapshot of the
   // current state for packet, and never updates internal state.
-  rtc::Optional<PacketState> GetPacketState(uint16_t sequence_number,
-                                            bool verify_rtt) const;
+  absl::optional<PacketState> GetPacketState(uint16_t sequence_number,
+                                             bool verify_rtt) const;
 
   // Get the packet (if any) from the history, with size closest to
   // |packet_size|. The exact size of the packet is not guaranteed.
@@ -101,7 +101,7 @@
     ~StoredPacket();
 
     // The time of last transmission, including retransmissions.
-    rtc::Optional<int64_t> send_time_ms;
+    absl::optional<int64_t> send_time_ms;
 
     // Number of times RE-transmitted, ie excluding the first transmission.
     size_t times_retransmitted = 0;
@@ -140,7 +140,7 @@
 
   // The earliest packet in the history. This might not be the lowest sequence
   // number, in case there is a wraparound.
-  rtc::Optional<uint16_t> start_seqno_ RTC_GUARDED_BY(lock_);
+  absl::optional<uint16_t> start_seqno_ RTC_GUARDED_BY(lock_);
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(RtpPacketHistory);
 };
diff --git a/modules/rtp_rtcp/source/rtp_packet_history_unittest.cc b/modules/rtp_rtcp/source/rtp_packet_history_unittest.cc
index c7cd180..026c187 100644
--- a/modules/rtp_rtcp/source/rtp_packet_history_unittest.cc
+++ b/modules/rtp_rtcp/source/rtp_packet_history_unittest.cc
@@ -62,7 +62,7 @@
   hist_.SetStorePacketsStatus(StorageMode::kStore, 10);
   // Store a packet, but with send-time. It should then not be removed.
   hist_.PutRtpPacket(CreateRtpPacket(kStartSeqNum), kAllowRetransmission,
-                     rtc::nullopt);
+                     absl::nullopt);
   EXPECT_TRUE(hist_.GetPacketState(kStartSeqNum, false));
 
   // Changing store status, even to the current one, will clear the history.
@@ -74,7 +74,7 @@
   hist_.SetStorePacketsStatus(StorageMode::kStoreAndCull, 10);
   // Store a packet, but with send-time. It should then not be removed.
   hist_.PutRtpPacket(CreateRtpPacket(kStartSeqNum), kAllowRetransmission,
-                     rtc::nullopt);
+                     absl::nullopt);
   EXPECT_TRUE(hist_.GetPacketState(kStartSeqNum, false));
 
   // Changing store status, to clear the history.
@@ -83,7 +83,7 @@
 
   // Add a new packet.
   hist_.PutRtpPacket(CreateRtpPacket(kStartSeqNum + 1), kAllowRetransmission,
-                     rtc::nullopt);
+                     absl::nullopt);
   EXPECT_TRUE(hist_.GetPacketState(kStartSeqNum + 1, false));
 
   // Advance time past where packet expires.
@@ -93,7 +93,7 @@
 
   // Add one more packet and verify no state left from packet before reset.
   hist_.PutRtpPacket(CreateRtpPacket(To16u(kStartSeqNum + 2)),
-                     kAllowRetransmission, rtc::nullopt);
+                     kAllowRetransmission, absl::nullopt);
   EXPECT_FALSE(hist_.GetPacketState(kStartSeqNum, false));
   EXPECT_TRUE(hist_.GetPacketState(kStartSeqNum + 1, false));
   EXPECT_TRUE(hist_.GetPacketState(To16u(kStartSeqNum + 2), false));
@@ -102,7 +102,7 @@
 TEST_F(RtpPacketHistoryTest, NoStoreStatus) {
   EXPECT_EQ(StorageMode::kDisabled, hist_.GetStorageMode());
   std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum);
-  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, rtc::nullopt);
+  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, absl::nullopt);
   // Packet should not be stored.
   EXPECT_FALSE(hist_.GetPacketState(kStartSeqNum, false));
 }
@@ -117,7 +117,7 @@
   std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum);
 
   EXPECT_FALSE(hist_.GetPacketState(kStartSeqNum, false));
-  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, rtc::nullopt);
+  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, absl::nullopt);
   EXPECT_TRUE(hist_.GetPacketState(kStartSeqNum, false));
 }
 
@@ -127,7 +127,7 @@
   std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum);
   packet->set_capture_time_ms(capture_time_ms);
   rtc::CopyOnWriteBuffer buffer = packet->Buffer();
-  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, rtc::nullopt);
+  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, absl::nullopt);
 
   std::unique_ptr<RtpPacketToSend> packet_out =
       hist_.GetPacketAndSetSendTime(kStartSeqNum, false);
@@ -143,7 +143,7 @@
   std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum);
   packet->set_capture_time_ms(-1);
   rtc::CopyOnWriteBuffer buffer = packet->Buffer();
-  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, rtc::nullopt);
+  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, absl::nullopt);
 
   std::unique_ptr<RtpPacketToSend> packet_out =
       hist_.GetPacketAndSetSendTime(kStartSeqNum, false);
@@ -157,7 +157,7 @@
   int64_t capture_time_ms = fake_clock_.TimeInMilliseconds();
   std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum);
   rtc::CopyOnWriteBuffer buffer = packet->Buffer();
-  hist_.PutRtpPacket(std::move(packet), kDontRetransmit, rtc::nullopt);
+  hist_.PutRtpPacket(std::move(packet), kDontRetransmit, absl::nullopt);
 
   // Get the packet and verify data.
   std::unique_ptr<RtpPacketToSend> packet_out;
@@ -182,7 +182,7 @@
   hist_.PutRtpPacket(std::move(packet), StorageType::kAllowRetransmission,
                      fake_clock_.TimeInMilliseconds());
 
-  rtc::Optional<RtpPacketHistory::PacketState> state =
+  absl::optional<RtpPacketHistory::PacketState> state =
       hist_.GetPacketState(kStartSeqNum, false);
   ASSERT_TRUE(state);
   EXPECT_EQ(state->rtp_sequence_number, kStartSeqNum);
@@ -208,7 +208,7 @@
   int64_t capture_time_ms = fake_clock_.TimeInMilliseconds();
   std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum);
   size_t len = packet->size();
-  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, rtc::nullopt);
+  hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, absl::nullopt);
 
   // First transmission: TimeToSendPacket() call from pacer.
   EXPECT_TRUE(hist_.GetPacketAndSetSendTime(kStartSeqNum, false));
@@ -223,7 +223,7 @@
   // 2) When the pacer determines that it is time to send the packet, it calls
   //    GetPacketAndSetSendTime(). This time we do not need to verify RTT as
   //    has that has already been done.
-  rtc::Optional<RtpPacketHistory::PacketState> packet_state =
+  absl::optional<RtpPacketHistory::PacketState> packet_state =
       hist_.GetPacketState(kStartSeqNum, /*verify_rtt=*/true);
   EXPECT_TRUE(packet_state);
   EXPECT_EQ(len, packet_state->payload_size);
@@ -313,7 +313,7 @@
   for (size_t i = 0; i < kMaxNumPackets; ++i) {
     std::unique_ptr<RtpPacketToSend> packet = CreateRtpPacket(kStartSeqNum + i);
     // Don't mark packets as sent, preventing them from being removed.
-    hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, rtc::nullopt);
+    hist_.PutRtpPacket(std::move(packet), kAllowRetransmission, absl::nullopt);
   }
 
   // First packet should still be there.
@@ -338,7 +338,7 @@
   for (size_t i = 0; i < kMaxNumPackets; ++i) {
     // Mark packets as unsent.
     hist_.PutRtpPacket(CreateRtpPacket(To16u(kStartSeqNum + i)),
-                       kAllowRetransmission, rtc::nullopt);
+                       kAllowRetransmission, absl::nullopt);
   }
   fake_clock_.AdvanceTimeMilliseconds(RtpPacketHistory::kMinPacketDurationMs);
 
diff --git a/modules/rtp_rtcp/source/rtp_payload_registry.cc b/modules/rtp_rtcp/source/rtp_payload_registry.cc
index 25abb68..c48cd6c 100644
--- a/modules/rtp_rtcp/source/rtp_payload_registry.cc
+++ b/modules/rtp_rtcp/source/rtp_payload_registry.cc
@@ -227,13 +227,13 @@
              : kVideoPayloadTypeFrequency;
 }
 
-rtc::Optional<RtpUtility::Payload> RTPPayloadRegistry::PayloadTypeToPayload(
+absl::optional<RtpUtility::Payload> RTPPayloadRegistry::PayloadTypeToPayload(
     uint8_t payload_type) const {
   rtc::CritScope cs(&crit_sect_);
   const auto it = payload_type_map_.find(payload_type);
   return it == payload_type_map_.end()
-             ? rtc::nullopt
-             : rtc::Optional<RtpUtility::Payload>(it->second);
+             ? absl::nullopt
+             : absl::optional<RtpUtility::Payload>(it->second);
 }
 
 }  // namespace webrtc
diff --git a/modules/rtp_rtcp/source/rtp_receiver_impl.cc b/modules/rtp_rtcp/source/rtp_receiver_impl.cc
index 5c5d68f..fb2cc66 100644
--- a/modules/rtp_rtcp/source/rtp_receiver_impl.cc
+++ b/modules/rtp_rtcp/source/rtp_receiver_impl.cc
@@ -29,7 +29,7 @@
 namespace webrtc {
 
 namespace {
-bool InOrderPacket(rtc::Optional<uint16_t> latest_sequence_number,
+bool InOrderPacket(absl::optional<uint16_t> latest_sequence_number,
                    uint16_t current_sequence_number) {
   if (!latest_sequence_number)
     return true;
@@ -174,8 +174,8 @@
 
   auto audio_level =
       rtp_header.extension.hasAudioLevel
-          ? rtc::Optional<uint8_t>(rtp_header.extension.audioLevel)
-          : rtc::nullopt;
+          ? absl::optional<uint8_t>(rtp_header.extension.audioLevel)
+          : absl::nullopt;
   UpdateSources(audio_level);
 
   int32_t ret_val = rtp_media_receiver_->ParseRtpPacket(
@@ -323,7 +323,7 @@
 }
 
 void RtpReceiverImpl::UpdateSources(
-    const rtc::Optional<uint8_t>& ssrc_audio_level) {
+    const absl::optional<uint8_t>& ssrc_audio_level) {
   rtc::CritScope lock(&critical_section_rtp_receiver_);
   int64_t now_ms = clock_->TimeInMilliseconds();
 
diff --git a/modules/rtp_rtcp/source/rtp_receiver_impl.h b/modules/rtp_rtcp/source/rtp_receiver_impl.h
index 3e78893..70d7a2e 100644
--- a/modules/rtp_rtcp/source/rtp_receiver_impl.h
+++ b/modules/rtp_rtcp/source/rtp_receiver_impl.h
@@ -16,7 +16,7 @@
 #include <unordered_map>
 #include <vector>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "modules/rtp_rtcp/include/rtp_receiver.h"
 #include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
 #include "modules/rtp_rtcp/source/rtp_receiver_strategy.h"
@@ -74,7 +74,7 @@
   int32_t CheckPayloadChanged(const RTPHeader& rtp_header,
                               PayloadUnion* payload);
 
-  void UpdateSources(const rtc::Optional<uint8_t>& ssrc_audio_level);
+  void UpdateSources(const absl::optional<uint8_t>& ssrc_audio_level);
   void RemoveOutdatedSources(int64_t now_ms);
 
   Clock* clock_;
@@ -91,7 +91,7 @@
       critical_section_rtp_receiver_);
 
   // Sequence number and timestamps for the latest in-order packet.
-  rtc::Optional<uint16_t> last_received_sequence_number_
+  absl::optional<uint16_t> last_received_sequence_number_
       RTC_GUARDED_BY(critical_section_rtp_receiver_);
   uint32_t last_received_timestamp_
       RTC_GUARDED_BY(critical_section_rtp_receiver_);
diff --git a/modules/rtp_rtcp/source/rtp_rtcp_impl.cc b/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
index 07a6afb..289ef53 100644
--- a/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
+++ b/modules/rtp_rtcp/source/rtp_rtcp_impl.cc
@@ -266,10 +266,10 @@
   rtp_sender_->SetRtxPayloadType(payload_type, associated_payload_type);
 }
 
-rtc::Optional<uint32_t> ModuleRtpRtcpImpl::FlexfecSsrc() const {
+absl::optional<uint32_t> ModuleRtpRtcpImpl::FlexfecSsrc() const {
   if (rtp_sender_)
     return rtp_sender_->FlexfecSsrc();
-  return rtc::nullopt;
+  return absl::nullopt;
 }
 
 void ModuleRtpRtcpImpl::IncomingRtcpPacket(const uint8_t* rtcp_packet,
@@ -898,7 +898,7 @@
   ssrcs.insert(main_ssrc);
   if (RtxSendStatus() != kRtxOff)
     ssrcs.insert(rtp_sender_->RtxSsrc());
-  rtc::Optional<uint32_t> flexfec_ssrc = FlexfecSsrc();
+  absl::optional<uint32_t> flexfec_ssrc = FlexfecSsrc();
   if (flexfec_ssrc)
     ssrcs.insert(*flexfec_ssrc);
   rtcp_receiver_.SetSsrcs(main_ssrc, ssrcs);
diff --git a/modules/rtp_rtcp/source/rtp_rtcp_impl.h b/modules/rtp_rtcp/source/rtp_rtcp_impl.h
index c51e971..9f53416 100644
--- a/modules/rtp_rtcp/source/rtp_rtcp_impl.h
+++ b/modules/rtp_rtcp/source/rtp_rtcp_impl.h
@@ -17,7 +17,7 @@
 #include <utility>
 #include <vector>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "api/video/video_bitrate_allocation.h"
 #include "modules/rtp_rtcp/include/rtp_rtcp.h"
 #include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
@@ -102,7 +102,7 @@
   void SetRtxSendPayloadType(int payload_type,
                              int associated_payload_type) override;
 
-  rtc::Optional<uint32_t> FlexfecSsrc() const override;
+  absl::optional<uint32_t> FlexfecSsrc() const override;
 
   // Sends kRtcpByeCode when going from true to false.
   int32_t SetSendingStatus(bool sending) override;
diff --git a/modules/rtp_rtcp/source/rtp_sender.cc b/modules/rtp_rtcp/source/rtp_sender.cc
index bf24c7d..8e0a4e8 100644
--- a/modules/rtp_rtcp/source/rtp_sender.cc
+++ b/modules/rtp_rtcp/source/rtp_sender.cc
@@ -630,7 +630,7 @@
 int32_t RTPSender::ReSendPacket(uint16_t packet_id) {
   // Try to find packet in RTP packet history. Also verify RTT here, so that we
   // don't retransmit too often.
-  rtc::Optional<RtpPacketHistory::PacketState> stored_packet =
+  absl::optional<RtpPacketHistory::PacketState> stored_packet =
       packet_history_.GetPacketState(packet_id, true);
   if (!stored_packet) {
     // Packet not found.
@@ -908,7 +908,7 @@
   }
 
   uint32_t ssrc = packet->Ssrc();
-  rtc::Optional<uint32_t> flexfec_ssrc = FlexfecSsrc();
+  absl::optional<uint32_t> flexfec_ssrc = FlexfecSsrc();
   if (paced_sender_) {
     uint16_t seq_no = packet->SequenceNumber();
     // Correct offset between implementations of millisecond time stamps in
@@ -919,9 +919,9 @@
       // Store FlexFEC packets in the history here, so they can be found
       // when the pacer calls TimeToSendPacket.
       flexfec_packet_history_.PutRtpPacket(std::move(packet), storage,
-                                           rtc::nullopt);
+                                           absl::nullopt);
     } else {
-      packet_history_.PutRtpPacket(std::move(packet), storage, rtc::nullopt);
+      packet_history_.PutRtpPacket(std::move(packet), storage, absl::nullopt);
     }
 
     paced_sender_->InsertPacket(priority, ssrc, seq_no, corrected_time_ms,
@@ -1155,11 +1155,11 @@
   mid_ = mid;
 }
 
-rtc::Optional<uint32_t> RTPSender::FlexfecSsrc() const {
+absl::optional<uint32_t> RTPSender::FlexfecSsrc() const {
   if (video_) {
     return video_->FlexfecSsrc();
   }
-  return rtc::nullopt;
+  return absl::nullopt;
 }
 
 void RTPSender::SetCsrcs(const std::vector<uint32_t>& csrcs) {
diff --git a/modules/rtp_rtcp/source/rtp_sender.h b/modules/rtp_rtcp/source/rtp_sender.h
index 61de2f1..5ff4a0f 100644
--- a/modules/rtp_rtcp/source/rtp_sender.h
+++ b/modules/rtp_rtcp/source/rtp_sender.h
@@ -17,9 +17,9 @@
 #include <utility>
 #include <vector>
 
+#include "absl/types/optional.h"
 #include "api/array_view.h"
 #include "api/call/transport.h"
-#include "api/optional.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "modules/rtp_rtcp/include/flexfec_sender.h"
 #include "modules/rtp_rtcp/include/rtp_header_extension_map.h"
@@ -172,7 +172,7 @@
 
   uint32_t SSRC() const;
 
-  rtc::Optional<uint32_t> FlexfecSsrc() const;
+  absl::optional<uint32_t> FlexfecSsrc() const;
 
   bool SendToNetwork(std::unique_ptr<RtpPacketToSend> packet,
                      StorageType storage,
@@ -315,9 +315,9 @@
   bool sequence_number_forced_ RTC_GUARDED_BY(send_critsect_);
   uint16_t sequence_number_ RTC_GUARDED_BY(send_critsect_);
   uint16_t sequence_number_rtx_ RTC_GUARDED_BY(send_critsect_);
-  // Must be explicitly set by the application, use of rtc::Optional
+  // Must be explicitly set by the application, use of absl::optional
   // only to keep track of correct use.
-  rtc::Optional<uint32_t> ssrc_ RTC_GUARDED_BY(send_critsect_);
+  absl::optional<uint32_t> ssrc_ RTC_GUARDED_BY(send_critsect_);
   // MID value to send in the MID header extension.
   std::string mid_ RTC_GUARDED_BY(send_critsect_);
   uint32_t last_rtp_timestamp_ RTC_GUARDED_BY(send_critsect_);
@@ -327,7 +327,7 @@
   bool last_packet_marker_bit_ RTC_GUARDED_BY(send_critsect_);
   std::vector<uint32_t> csrcs_ RTC_GUARDED_BY(send_critsect_);
   int rtx_ RTC_GUARDED_BY(send_critsect_);
-  rtc::Optional<uint32_t> ssrc_rtx_ RTC_GUARDED_BY(send_critsect_);
+  absl::optional<uint32_t> ssrc_rtx_ RTC_GUARDED_BY(send_critsect_);
   // Mapping rtx_payload_type_map_[associated] = rtx.
   std::map<int8_t, int8_t> rtx_payload_type_map_ RTC_GUARDED_BY(send_critsect_);
   size_t rtp_overhead_bytes_per_packet_ RTC_GUARDED_BY(send_critsect_);
diff --git a/modules/rtp_rtcp/source/rtp_sender_video.cc b/modules/rtp_rtcp/source/rtp_sender_video.cc
index b5515c5..efac87c 100644
--- a/modules/rtp_rtcp/source/rtp_sender_video.cc
+++ b/modules/rtp_rtcp/source/rtp_sender_video.cc
@@ -264,11 +264,11 @@
   key_fec_params_ = key_params;
 }
 
-rtc::Optional<uint32_t> RTPSenderVideo::FlexfecSsrc() const {
+absl::optional<uint32_t> RTPSenderVideo::FlexfecSsrc() const {
   if (flexfec_sender_) {
     return flexfec_sender_->ssrc();
   }
-  return rtc::nullopt;
+  return absl::nullopt;
 }
 
 bool RTPSenderVideo::SendVideo(enum VideoCodecType video_type,
@@ -503,7 +503,7 @@
       int64_t expected_next_frame_time = kUndefined;
       for (int i = temporal_id - 1; i >= 0; --i) {
         TemporalLayerStats* stats = &frame_stats_by_temporal_layer_[i];
-        rtc::Optional<uint32_t> rate = stats->frame_rate_fp1000s.Rate(now_ms);
+        absl::optional<uint32_t> rate = stats->frame_rate_fp1000s.Rate(now_ms);
         if (rate) {
           int64_t tl_next = stats->last_frame_time_ms + 1000000 / *rate;
           if (tl_next - now_ms > -expected_retransmission_time_ms &&
diff --git a/modules/rtp_rtcp/source/rtp_sender_video.h b/modules/rtp_rtcp/source/rtp_sender_video.h
index 13ed4c4..08724c7 100644
--- a/modules/rtp_rtcp/source/rtp_sender_video.h
+++ b/modules/rtp_rtcp/source/rtp_sender_video.h
@@ -14,7 +14,7 @@
 #include <map>
 #include <memory>
 
-#include "api/optional.h"
+#include "absl/types/optional.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "modules/rtp_rtcp/include/flexfec_sender.h"
 #include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"
@@ -70,7 +70,7 @@
                         const FecProtectionParams& key_params);
 
   // FlexFEC.
-  rtc::Optional<uint32_t> FlexfecSsrc() const;
+  absl::optional<uint32_t> FlexfecSsrc() const;
 
   uint32_t VideoBitrateSent() const;
   uint32_t FecOverheadRate() const;