diff -u b/core/modules/big_pipe/src/Render/BigPipeInterface.php b/core/modules/big_pipe/src/Render/BigPipeInterface.php
--- b/core/modules/big_pipe/src/Render/BigPipeInterface.php
+++ b/core/modules/big_pipe/src/Render/BigPipeInterface.php
@@ -128,10 +128,6 @@
  *
  * @see \Drupal\big_pipe\EventSubscriber\HtmlResponseBigPipeSubscriber
  * @see \Drupal\big_pipe\Render\Placeholder\BigPipeStrategy
- *
- * @internal
- *   This object is marked as internal because it should only be used in the
- *   BigPipe render pipeline.
  */
 interface BigPipeInterface {
 
@@ -142,6 +138,12 @@
    *   The HTML response content to send.
    * @param array $attachments
    *   The HTML response's attachments.
+   *
+   * @internal
+   *   This method should only be invoked by
+   *   \Drupal\big_pipe\Render\BigPipeResponse, which is itself an internal
+   *   class. Furthermore, the signature of this method will change in
+   *   https://www.drupal.org/node/2657684.
    */
   public function sendContent($content, array $attachments);
 
diff -u b/core/modules/big_pipe/src/Render/BigPipeResponse.php b/core/modules/big_pipe/src/Render/BigPipeResponse.php
--- b/core/modules/big_pipe/src/Render/BigPipeResponse.php
+++ b/core/modules/big_pipe/src/Render/BigPipeResponse.php
@@ -14,10 +14,9 @@
  * @see \Drupal\big_pipe\Render\BigPipeInterface
  *
  * @internal
- *   This object is marked as internal because it should only be used in the
- *   BigPipe render pipeline.
- *
- * @todo Will become obsolete with https://www.drupal.org/node/2577631
+ *   This is a temporary solution until a generic response emitter interface is
+ *   created in https://www.drupal.org/node/2577631. Only code internal to
+ *   BigPipe should instantiate or type hint to this class.
  */
 class BigPipeResponse extends HtmlResponse {