diff --git a/api/peerconnectioninterface.h b/api/peerconnectioninterface.h
index 9e26df5594..192a39a830 100644
--- a/api/peerconnectioninterface.h
+++ b/api/peerconnectioninterface.h
@@ -976,27 +976,22 @@ class PeerConnectionInterface : public rtc::RefCountInterface {
 // Application should implement these methods.
 class PeerConnectionObserver {
  public:
-  enum StateType {
-    kSignalingState,
-    kIceState,
-  };
-
   virtual ~PeerConnectionObserver() = default;
 
   // Triggered when the SignalingState changed.
   virtual void OnSignalingChange(
       PeerConnectionInterface::SignalingState new_state) = 0;
 
-  // TODO(deadbeef): Once all subclasses override the scoped_refptr versions
-  // of the below three methods, make them pure virtual and remove the raw
-  // pointer version.
-
   // Triggered when media is received on a new stream from remote peer.
-  virtual void OnAddStream(rtc::scoped_refptr<MediaStreamInterface> stream) = 0;
+  // Deprecated: This callback will no longer be fired with Unified Plan
+  // semantics. Consider switching to OnAddTrack.
+  virtual void OnAddStream(rtc::scoped_refptr<MediaStreamInterface> stream) {}
 
   // Triggered when a remote peer close a stream.
-  virtual void OnRemoveStream(
-      rtc::scoped_refptr<MediaStreamInterface> stream) = 0;
+  // Deprecated: This callback will no longer be fired with Unified Plan
+  // semantics.
+  virtual void OnRemoveStream(rtc::scoped_refptr<MediaStreamInterface> stream) {
+  }
 
   // Triggered when a remote peer opens a data channel.
   virtual void OnDataChannel(