diff --git a/src/internal/AsyncSubject.ts b/src/internal/AsyncSubject.ts
index 49e97caa67..09d4a54006 100644
--- a/src/internal/AsyncSubject.ts
+++ b/src/internal/AsyncSubject.ts
@@ -10,7 +10,8 @@ export class AsyncSubject<T> extends Subject<T> {
   private hasNext: boolean = false;
   private hasCompleted: boolean = false;
 
-  protected _subscribe(subscriber: Subscriber<any>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<any>): Subscription {
     if (this.hasError) {
       subscriber.error(this.thrownError);
       return Subscription.EMPTY;
diff --git a/src/internal/BehaviorSubject.ts b/src/internal/BehaviorSubject.ts
index a91407088e..3a11d264b3 100644
--- a/src/internal/BehaviorSubject.ts
+++ b/src/internal/BehaviorSubject.ts
@@ -17,7 +17,8 @@ export class BehaviorSubject<T> extends Subject<T> {
     return this.getValue();
   }
 
-  protected _subscribe(subscriber: Subscriber<T>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>): Subscription {
     const subscription = super._subscribe(subscriber);
     if (subscription && !(<SubscriptionLike>subscription).closed) {
       subscriber.next(this._value);
diff --git a/src/internal/Observable.ts b/src/internal/Observable.ts
index 1620e8bf03..237e2bbfe7 100644
--- a/src/internal/Observable.ts
+++ b/src/internal/Observable.ts
@@ -21,9 +21,11 @@ export class Observable<T> implements Subscribable<T> {
   /** Internal implementation detail, do not use directly. */
   public _isScalar: boolean = false;
 
-  protected source: Observable<any>;
+  /** @deprecated This is an internal implementation detail, do not use. */
+  source: Observable<any>;
 
-  protected operator: Operator<any, T>;
+  /** @deprecated This is an internal implementation detail, do not use. */
+  operator: Operator<any, T>;
 
   /**
    * @constructor
@@ -208,7 +210,8 @@ export class Observable<T> implements Subscribable<T> {
     return sink;
   }
 
-  protected _trySubscribe(sink: Subscriber<T>): TeardownLogic {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _trySubscribe(sink: Subscriber<T>): TeardownLogic {
     try {
       return this._subscribe(sink);
     } catch (err) {
@@ -247,8 +250,8 @@ export class Observable<T> implements Subscribable<T> {
     }) as Promise<void>;
   }
 
-  /** @internal */
-  protected _subscribe(subscriber: Subscriber<any>): TeardownLogic {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<any>): TeardownLogic {
     const { source } = this;
     return source && source.subscribe(subscriber);
   }
diff --git a/src/internal/ReplaySubject.ts b/src/internal/ReplaySubject.ts
index 171cc48581..5f4fc0928f 100644
--- a/src/internal/ReplaySubject.ts
+++ b/src/internal/ReplaySubject.ts
@@ -49,7 +49,8 @@ export class ReplaySubject<T> extends Subject<T> {
     super.next(value);
   }
 
-  protected _subscribe(subscriber: Subscriber<T>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>): Subscription {
     // When `_infiniteTimeWindow === true` then the buffer is already trimmed
     const _infiniteTimeWindow = this._infiniteTimeWindow;
     const _events = _infiniteTimeWindow ? this._events : this._trimBufferThenGetEvents();
diff --git a/src/internal/Subject.ts b/src/internal/Subject.ts
index bbb39eaa6c..4ce87298b3 100644
--- a/src/internal/Subject.ts
+++ b/src/internal/Subject.ts
@@ -100,7 +100,8 @@ export class Subject<T> extends Observable<T> implements SubscriptionLike {
     this.observers = null;
   }
 
-  protected _trySubscribe(subscriber: Subscriber<T>): TeardownLogic {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _trySubscribe(subscriber: Subscriber<T>): TeardownLogic {
     if (this.closed) {
       throw new ObjectUnsubscribedError();
     } else {
@@ -108,7 +109,8 @@ export class Subject<T> extends Observable<T> implements SubscriptionLike {
     }
   }
 
-  protected _subscribe(subscriber: Subscriber<T>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>): Subscription {
     if (this.closed) {
       throw new ObjectUnsubscribedError();
     } else if (this.hasError) {
@@ -160,7 +162,8 @@ export class AnonymousSubject<T> extends Subject<T> {
     }
   }
 
-  protected _subscribe(subscriber: Subscriber<T>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>): Subscription {
     const { source } = this;
     if (source) {
       return this.source.subscribe(subscriber);
diff --git a/src/internal/Subscriber.ts b/src/internal/Subscriber.ts
index 35d60b3d38..f7ad950a49 100644
--- a/src/internal/Subscriber.ts
+++ b/src/internal/Subscriber.ts
@@ -152,7 +152,8 @@ export class Subscriber<T> extends Subscription implements Observer<T> {
     this.unsubscribe();
   }
 
-  protected _unsubscribeAndRecycle(): Subscriber<T> {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribeAndRecycle(): Subscriber<T> {
     const { _parent, _parents } = this;
     this._parent = null;
     this._parents = null;
@@ -296,7 +297,8 @@ class SafeSubscriber<T> extends Subscriber<T> {
     return false;
   }
 
-  protected _unsubscribe(): void {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe(): void {
     const { _parentSubscriber } = this;
     this._context = null;
     this._parentSubscriber = null;
diff --git a/src/internal/observable/ConnectableObservable.ts b/src/internal/observable/ConnectableObservable.ts
index e3e887eea6..44d6fd9998 100644
--- a/src/internal/observable/ConnectableObservable.ts
+++ b/src/internal/observable/ConnectableObservable.ts
@@ -17,12 +17,13 @@ export class ConnectableObservable<T> extends Observable<T> {
   /** @internal */
   _isComplete = false;
 
-  constructor(protected source: Observable<T>,
+  constructor(public source: Observable<T>,
               protected subjectFactory: () => Subject<T>) {
     super();
   }
 
-  protected _subscribe(subscriber: Subscriber<T>) {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>) {
     return this.getSubject().subscribe(subscriber);
   }
 
diff --git a/src/internal/observable/SubscribeOnObservable.ts b/src/internal/observable/SubscribeOnObservable.ts
index 64839cf63c..d66e3b100d 100644
--- a/src/internal/observable/SubscribeOnObservable.ts
+++ b/src/internal/observable/SubscribeOnObservable.ts
@@ -39,7 +39,8 @@ export class SubscribeOnObservable<T> extends Observable<T> {
     }
   }
 
-  protected _subscribe(subscriber: Subscriber<T>) {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>) {
     const delay = this.delayTime;
     const source = this.source;
     const scheduler = this.scheduler;
diff --git a/src/internal/observable/dom/AjaxObservable.ts b/src/internal/observable/dom/AjaxObservable.ts
index 51de1dcbc2..d708d39c69 100644
--- a/src/internal/observable/dom/AjaxObservable.ts
+++ b/src/internal/observable/dom/AjaxObservable.ts
@@ -179,7 +179,8 @@ export class AjaxObservable<T> extends Observable<T> {
     this.request = request;
   }
 
-  protected _subscribe(subscriber: Subscriber<T>): TeardownLogic {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>): TeardownLogic {
     return new AjaxSubscriber(subscriber, this.request);
   }
 }
diff --git a/src/internal/observable/dom/WebSocketSubject.ts b/src/internal/observable/dom/WebSocketSubject.ts
index 76a015dd17..ee68790e17 100644
--- a/src/internal/observable/dom/WebSocketSubject.ts
+++ b/src/internal/observable/dom/WebSocketSubject.ts
@@ -68,7 +68,8 @@ export class WebSocketSubject<T> extends AnonymousSubject<T> {
 
   private _config: WebSocketSubjectConfig<T>;
 
-  protected _output: Subject<T>;
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _output: Subject<T>;
 
   private _socket: WebSocket;
 
@@ -263,7 +264,8 @@ export class WebSocketSubject<T> extends AnonymousSubject<T> {
     };
   }
 
-  protected _subscribe(subscriber: Subscriber<T>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>): Subscription {
     const { source } = this;
     if (source) {
       return source.subscribe(subscriber);
diff --git a/src/internal/operators/bufferTime.ts b/src/internal/operators/bufferTime.ts
index ceed50ea0d..11f9205cc3 100644
--- a/src/internal/operators/bufferTime.ts
+++ b/src/internal/operators/bufferTime.ts
@@ -170,7 +170,8 @@ class BufferTimeSubscriber<T> extends Subscriber<T> {
     super._complete();
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     this.contexts = null;
   }
 
diff --git a/src/internal/operators/bufferWhen.ts b/src/internal/operators/bufferWhen.ts
index 96a69d0c7c..5dc40404af 100644
--- a/src/internal/operators/bufferWhen.ts
+++ b/src/internal/operators/bufferWhen.ts
@@ -85,7 +85,8 @@ class BufferWhenSubscriber<T> extends OuterSubscriber<T, any> {
     super._complete();
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     this.buffer = null;
     this.subscribing = false;
   }
diff --git a/src/internal/operators/delayWhen.ts b/src/internal/operators/delayWhen.ts
index 730d7cb9cf..f2c0d4a702 100644
--- a/src/internal/operators/delayWhen.ts
+++ b/src/internal/operators/delayWhen.ts
@@ -161,11 +161,12 @@ class DelayWhenSubscriber<T, R> extends OuterSubscriber<T, R> {
  * @extends {Ignored}
  */
 class SubscriptionDelayObservable<T> extends Observable<T> {
-  constructor(protected source: Observable<T>, private subscriptionDelay: Observable<any>) {
+  constructor(public source: Observable<T>, private subscriptionDelay: Observable<any>) {
     super();
   }
 
-  protected _subscribe(subscriber: Subscriber<T>) {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>) {
     this.subscriptionDelay.subscribe(new SubscriptionDelaySubscriber(subscriber, this.source));
   }
 }
diff --git a/src/internal/operators/groupBy.ts b/src/internal/operators/groupBy.ts
index fd6ab94f90..cf2e0fb7c5 100644
--- a/src/internal/operators/groupBy.ts
+++ b/src/internal/operators/groupBy.ts
@@ -234,7 +234,8 @@ class GroupDurationSubscriber<K, T> extends Subscriber<T> {
     this.complete();
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     const { parent, key } = this;
     this.key = this.parent = null;
     if (parent) {
@@ -258,7 +259,8 @@ export class GroupedObservable<K, T> extends Observable<T> {
     super();
   }
 
-  protected _subscribe(subscriber: Subscriber<T>) {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<T>) {
     const subscription = new Subscription();
     const { refCountSubscription, groupSubject } = this;
     if (refCountSubscription && !refCountSubscription.closed) {
diff --git a/src/internal/operators/repeatWhen.ts b/src/internal/operators/repeatWhen.ts
index 1af2e86f59..8bfe3e4b1d 100644
--- a/src/internal/operators/repeatWhen.ts
+++ b/src/internal/operators/repeatWhen.ts
@@ -86,7 +86,8 @@ class RepeatWhenSubscriber<T, R> extends OuterSubscriber<T, R> {
     }
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     const { notifications, retriesSubscription } = this;
     if (notifications) {
       notifications.unsubscribe();
@@ -99,7 +100,8 @@ class RepeatWhenSubscriber<T, R> extends OuterSubscriber<T, R> {
     this.retries = null;
   }
 
-  protected _unsubscribeAndRecycle(): Subscriber<T> {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribeAndRecycle(): Subscriber<T> {
     const { _unsubscribe } = this;
 
     this._unsubscribe = null;
diff --git a/src/internal/operators/retryWhen.ts b/src/internal/operators/retryWhen.ts
index 616c618bbf..ec4c402e5e 100644
--- a/src/internal/operators/retryWhen.ts
+++ b/src/internal/operators/retryWhen.ts
@@ -86,7 +86,8 @@ class RetryWhenSubscriber<T, R> extends OuterSubscriber<T, R> {
     }
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     const { errors, retriesSubscription } = this;
     if (errors) {
       errors.unsubscribe();
diff --git a/src/internal/operators/timeoutWith.ts b/src/internal/operators/timeoutWith.ts
index 85104dcb7a..75458c80a1 100644
--- a/src/internal/operators/timeoutWith.ts
+++ b/src/internal/operators/timeoutWith.ts
@@ -129,7 +129,8 @@ class TimeoutWithSubscriber<T, R> extends OuterSubscriber<T, R> {
     super._next(value);
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     this.action = null;
     this.scheduler = null;
     this.withObservable = null;
diff --git a/src/internal/operators/window.ts b/src/internal/operators/window.ts
index 9da0851085..d0dba99435 100644
--- a/src/internal/operators/window.ts
+++ b/src/internal/operators/window.ts
@@ -106,7 +106,8 @@ class WindowSubscriber<T> extends OuterSubscriber<T, any> {
     this.destination.complete();
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     this.window = null;
   }
 
diff --git a/src/internal/operators/windowToggle.ts b/src/internal/operators/windowToggle.ts
index c3543c479e..4a6a36b205 100644
--- a/src/internal/operators/windowToggle.ts
+++ b/src/internal/operators/windowToggle.ts
@@ -134,7 +134,8 @@ class WindowToggleSubscriber<T, O> extends OuterSubscriber<T, any> {
     super._complete();
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
     const { contexts } = this;
     this.contexts = null;
     if (contexts) {
diff --git a/src/internal/scheduler/AsyncAction.ts b/src/internal/scheduler/AsyncAction.ts
index c898cdbedb..d61502e3e8 100644
--- a/src/internal/scheduler/AsyncAction.ts
+++ b/src/internal/scheduler/AsyncAction.ts
@@ -129,7 +129,8 @@ export class AsyncAction<T> extends Action<T> {
     }
   }
 
-  protected _unsubscribe() {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _unsubscribe() {
 
     const id = this.id;
     const scheduler = this.scheduler;
diff --git a/src/internal/testing/HotObservable.ts b/src/internal/testing/HotObservable.ts
index 8918890ab9..28a94a4e95 100644
--- a/src/internal/testing/HotObservable.ts
+++ b/src/internal/testing/HotObservable.ts
@@ -24,7 +24,8 @@ export class HotObservable<T> extends Subject<T> implements SubscriptionLoggable
     this.scheduler = scheduler;
   }
 
-  protected _subscribe(subscriber: Subscriber<any>): Subscription {
+  /** @deprecated This is an internal implementation detail, do not use. */
+  _subscribe(subscriber: Subscriber<any>): Subscription {
     const subject: HotObservable<T> = this;
     const index = subject.logSubscribedFrame();
     subscriber.add(new Subscription(() => {