diff --git a/RELEASE-NOTES-1.38 b/RELEASE-NOTES-1.38
index 47187e8aa6e..2d0fa91ebda 100644
--- a/RELEASE-NOTES-1.38
+++ b/RELEASE-NOTES-1.38
@@ -21,6 +21,8 @@ For notes on 1.37.x and older releases, see HISTORY.
 === Configuration changes for system administrators in 1.38 ===
 * Deprecate $wgAjaxUploadDestCheck, act as always-true
 * $wgInterwikiCache no longer supports the string value for CDB files.
+* Deprecate $wgParserOutputHooks; These should be done with
+  OutputPageParserOutputHook instead. (T292321)
 * …
 
 ==== New configuration ====
@@ -483,6 +485,8 @@ because of Phabricator reports.
    - ::setFlag() - use ::setOutputFlag()
    - ::getAllFlags() - this method is now marked @internal
    - ::addJsConfigVars() - use ::setJsConfigVar() or ::appendJsConfigVar()
+   - ::addOutputHook() / ::getOutputHooks() - these hooks should be migrated
+     to use the OutputPageParserOutput hook instead
 * The use of ParserOutput::setExtensionData() to overwrite previous values
   stored under a given key has been deprecated; use the new
   ::appendExtensionData() to collect multiple values in the ParserOutput
diff --git a/includes/DefaultSettings.php b/includes/DefaultSettings.php
index a32766588ac..ac3cd106f0e 100644
--- a/includes/DefaultSettings.php
+++ b/includes/DefaultSettings.php
@@ -8546,6 +8546,8 @@ $wgExtensionEntryPointListFiles = [];
  * @code
  *    function outputHook( $outputPage, $parserOutput, $data ) { ... }
  * @endcode
+ * @deprecated since 1.38; should be done with extensionData and the
+ *  OutputPageParserOutputHook (T292321).
  */
 $wgParserOutputHooks = [];
 
diff --git a/includes/OutputPage.php b/includes/OutputPage.php
index f55b520270c..7a506e9d559 100644
--- a/includes/OutputPage.php
+++ b/includes/OutputPage.php
@@ -1996,6 +1996,8 @@ class OutputPage extends ContextSource {
 		}
 
 		// Hooks registered in the object
+		// Deprecated! See T292321; should be done in the OutputPageParserOutput
+		// hook instead.
 		$parserOutputHooks = $this->getConfig()->get( 'ParserOutputHooks' );
 		foreach ( $parserOutput->getOutputHooks() as $hookInfo ) {
 			list( $hookName, $data ) = $hookInfo;
diff --git a/includes/parser/ParserOutput.php b/includes/parser/ParserOutput.php
index d46080f1059..a1a536cedb1 100644
--- a/includes/parser/ParserOutput.php
+++ b/includes/parser/ParserOutput.php
@@ -784,6 +784,11 @@ class ParserOutput extends CacheTime implements ContentMetadataCollector {
 		return $result;
 	}
 
+	/**
+	 * @return array
+	 * @deprecated since 1.38; should be done in the OutputPageParserOutput
+	 * hook (T292321).
+	 */
 	public function getOutputHooks(): array {
 		return (array)$this->mOutputHooks;
 	}
@@ -949,6 +954,12 @@ class ParserOutput extends CacheTime implements ContentMetadataCollector {
 		$this->mWarnings[$s] = 1;
 	}
 
+	/**
+	 * @param callable $hook
+	 * @param mixed $data
+	 * @deprecated since 1.38; should be done in the OutputPageParserOutput
+	 * hook (T292321).
+	 */
 	public function addOutputHook( $hook, $data = false ): void {
 		$this->mOutputHooks[] = [ $hook, $data ];
 	}