diff --git a/.github/changelog/2973-from-description b/.github/changelog/2973-from-description
new file mode 100644
index 000000000..d5f525f4e
--- /dev/null
+++ b/.github/changelog/2973-from-description
@@ -0,0 +1,4 @@
+Significance: patch
+Type: added
+
+Add backwards compatibility for the `ACTIVITYPUB_DISABLE_SIDELOADING` constant and `activitypub_sideloading_enabled` filter from version 7.9.1.
diff --git a/includes/class-cache.php b/includes/class-cache.php
index 4e81fac5e..1bbaaeaad 100644
--- a/includes/class-cache.php
+++ b/includes/class-cache.php
@@ -42,7 +42,22 @@ public static function init() {
 	 */
 	public static function is_enabled() {
 		// Check constant first.
-		if ( ACTIVITYPUB_DISABLE_MEDIA_CACHE ) {
+		if ( ACTIVITYPUB_DISABLE_REMOTE_CACHE ) {
+			return false;
+		}
+
+		/**
+		 * Filters whether sideloading is enabled.
+		 *
+		 * This filter was introduced in 7.9.1 and replaced by
+		 * {@see 'activitypub_remote_cache_enabled'} in a subsequent release.
+		 *
+		 * @since 7.9.1
+		 * @deprecated unreleased Use {@see 'activitypub_remote_cache_enabled'} instead.
+		 *
+		 * @param bool $enabled Whether sideloading is enabled. Default true.
+		 */
+		if ( ! \apply_filters_deprecated( 'activitypub_sideloading_enabled', array( true ), 'unreleased', 'activitypub_remote_cache_enabled' ) ) {
 			return false;
 		}
 
diff --git a/includes/constants.php b/includes/constants.php
index 5c251d3d9..7a40b895b 100644
--- a/includes/constants.php
+++ b/includes/constants.php
@@ -20,7 +20,11 @@
 defined( 'ACTIVITYPUB_DISABLE_OUTGOING_INTERACTIONS' ) || define( 'ACTIVITYPUB_DISABLE_OUTGOING_INTERACTIONS', false );
 defined( 'ACTIVITYPUB_DEFAULT_OBJECT_TYPE' ) || define( 'ACTIVITYPUB_DEFAULT_OBJECT_TYPE', 'wordpress-post-format' );
 defined( 'ACTIVITYPUB_OUTBOX_PROCESSING_BATCH_SIZE' ) || define( 'ACTIVITYPUB_OUTBOX_PROCESSING_BATCH_SIZE', 100 );
-defined( 'ACTIVITYPUB_DISABLE_MEDIA_CACHE' ) || define( 'ACTIVITYPUB_DISABLE_MEDIA_CACHE', false );
+// Backwards compatibility: map old ACTIVITYPUB_DISABLE_SIDELOADING to ACTIVITYPUB_DISABLE_REMOTE_CACHE.
+if ( ! defined( 'ACTIVITYPUB_DISABLE_REMOTE_CACHE' ) && defined( 'ACTIVITYPUB_DISABLE_SIDELOADING' ) ) {
+	define( 'ACTIVITYPUB_DISABLE_REMOTE_CACHE', ACTIVITYPUB_DISABLE_SIDELOADING );
+}
+defined( 'ACTIVITYPUB_DISABLE_REMOTE_CACHE' ) || define( 'ACTIVITYPUB_DISABLE_REMOTE_CACHE', false );
 
 // The following constants are invariable and define values used throughout the plugin.
 
diff --git a/readme.txt b/readme.txt
index d814e222e..eff895694 100644
--- a/readme.txt
+++ b/readme.txt
@@ -89,6 +89,7 @@ The plugin uses PHP Constants to enable, disable or change its default behaviour
 * `ACTIVITYPUB_DISABLE_REWRITES` - Disable auto generation of `mod_rewrite` rules. Default: `false`.
 * `ACTIVITYPUB_DISABLE_INCOMING_INTERACTIONS` - Block incoming replies/comments/likes. Default: `false`.
 * `ACTIVITYPUB_DISABLE_OUTGOING_INTERACTIONS` - Disable outgoing replies/comments/likes. Default: `false`.
+* `ACTIVITYPUB_DISABLE_REMOTE_CACHE` - Disable remote media caching (avatars, media, emoji). Default: `false`. Replaces `ACTIVITYPUB_DISABLE_SIDELOADING` from 7.9.1.
 * `ACTIVITYPUB_SHARED_INBOX_FEATURE` - Enable the shared inbox. Default: `false`.
 * `ACTIVITYPUB_SEND_VARY_HEADER` - Enable to send the `Vary: Accept` header. Default: `false`.
 
diff --git a/tests/phpunit/tests/includes/class-test-cache.php b/tests/phpunit/tests/includes/class-test-cache.php
index 77abd74cb..c9fd278d1 100644
--- a/tests/phpunit/tests/includes/class-test-cache.php
+++ b/tests/phpunit/tests/includes/class-test-cache.php
@@ -36,6 +36,17 @@ public function test_is_enabled_filter() {
 		$this->assertTrue( Cache::is_enabled() );
 	}
 
+	/**
+	 * Test is_enabled respects deprecated sideloading filter.
+	 */
+	public function test_is_enabled_deprecated_sideloading_filter() {
+		$this->setExpectedDeprecated( 'activitypub_sideloading_enabled' );
+
+		add_filter( 'activitypub_sideloading_enabled', '__return_false' );
+		$this->assertFalse( Cache::is_enabled() );
+		remove_filter( 'activitypub_sideloading_enabled', '__return_false' );
+	}
+
 	/**
 	 * Test init does not run when disabled.
 	 */