diff --git a/api/media_transport_interface.cc b/api/media_transport_interface.cc
index a97b7894cc..cb2fdabc5c 100644
--- a/api/media_transport_interface.cc
+++ b/api/media_transport_interface.cc
@@ -85,19 +85,6 @@ MediaTransportEncodedVideoFrame::MediaTransportEncodedVideoFrame(
 
 SendDataParams::SendDataParams() = default;
 
-RTCError MediaTransportInterface::SendData(
-    int channel_id,
-    const SendDataParams& params,
-    const rtc::CopyOnWriteBuffer& buffer) {
-  RTC_NOTREACHED();
-  return RTCError(RTCErrorType::UNSUPPORTED_OPERATION, "Not implemented");
-}
-
-RTCError MediaTransportInterface::CloseChannel(int channel_id) {
-  RTC_NOTREACHED();
-  return RTCError(RTCErrorType::UNSUPPORTED_OPERATION, "Not implemented");
-}
-
 RTCErrorOr<std::unique_ptr<MediaTransportInterface>>
 MediaTransportFactory::CreateMediaTransport(
     rtc::PacketTransportInternal* packet_transport,
diff --git a/api/media_transport_interface.h b/api/media_transport_interface.h
index e0e7453067..4eb55c4336 100644
--- a/api/media_transport_interface.h
+++ b/api/media_transport_interface.h
@@ -336,29 +336,25 @@ class MediaTransportInterface {
   // callback must be unregistered by setting it to nullptr.
   // A newly registered callback will be called with the current state.
   // Media transport does not invoke this callback concurrently.
-  // TODO(mellem): Make this pure virtual once all implementations support it.
   virtual void SetMediaTransportStateCallback(
-      MediaTransportStateCallback* callback) {}
+      MediaTransportStateCallback* callback) = 0;
 
   // Sends a data buffer to the remote endpoint using the given send parameters.
   // |buffer| may not be larger than 256 KiB. Returns an error if the send
   // fails.
-  // TODO(mellem): Make this pure virtual once all implementations support it.
   virtual RTCError SendData(int channel_id,
                             const SendDataParams& params,
-                            const rtc::CopyOnWriteBuffer& buffer);
+                            const rtc::CopyOnWriteBuffer& buffer) = 0;
 
   // Closes |channel_id| gracefully.  Returns an error if |channel_id| is not
   // open.  Data sent after the closing procedure begins will not be
   // transmitted. The channel becomes closed after pending data is transmitted.
-  // TODO(mellem): Make this pure virtual once all implementations support it.
-  virtual RTCError CloseChannel(int channel_id);
+  virtual RTCError CloseChannel(int channel_id) = 0;
 
   // Sets a sink for data messages and channel state callbacks. Before media
   // transport is destroyed, the sink must be unregistered by setting it to
   // nullptr.
-  // TODO(mellem): Make this pure virtual once all implementations support it.
-  virtual void SetDataSink(DataChannelSink* sink) {}
+  virtual void SetDataSink(DataChannelSink* sink) = 0;
 
   // TODO(sukhanov): RtcEventLogs.
 };
diff --git a/api/test/fake_media_transport.h b/api/test/fake_media_transport.h
index 5609126941..1ef7c1f3e4 100644
--- a/api/test/fake_media_transport.h
+++ b/api/test/fake_media_transport.h
@@ -57,6 +57,19 @@ class FakeMediaTransport : public MediaTransportInterface {
   void SetTargetTransferRateObserver(
       webrtc::TargetTransferRateObserver* observer) override {}
 
+  void SetMediaTransportStateCallback(
+      MediaTransportStateCallback* callback) override {}
+
+  RTCError SendData(int channel_id,
+                    const SendDataParams& params,
+                    const rtc::CopyOnWriteBuffer& buffer) override {
+    return RTCError::OK();
+  }
+
+  RTCError CloseChannel(int channel_id) override { return RTCError::OK(); }
+
+  void SetDataSink(DataChannelSink* sink) override {}
+
  private:
   const MediaTransportSettings settings_;
 };
diff --git a/api/test/loopback_media_transport.h b/api/test/loopback_media_transport.h
index 3195f979ba..9ce50a7c8c 100644
--- a/api/test/loopback_media_transport.h
+++ b/api/test/loopback_media_transport.h
@@ -64,6 +64,21 @@ class MediaTransportPair {
     void SetTargetTransferRateObserver(
         webrtc::TargetTransferRateObserver* observer) override {}
 
+    void SetMediaTransportStateCallback(
+        MediaTransportStateCallback* callback) override {}
+
+    RTCError SendData(int channel_id,
+                      const SendDataParams& params,
+                      const rtc::CopyOnWriteBuffer& buffer) override {
+      return RTCError(RTCErrorType::UNSUPPORTED_OPERATION, "Not implemented");
+    }
+
+    RTCError CloseChannel(int channel_id) override {
+      return RTCError(RTCErrorType::UNSUPPORTED_OPERATION, "Not implemented");
+    }
+
+    void SetDataSink(DataChannelSink* sink) override {}
+
    private:
     void OnData(uint64_t channel_id, MediaTransportEncodedAudioFrame frame) {
       if (sink_) {