diff --git src/wp-admin/includes/class-core-upgrader.php src/wp-admin/includes/class-core-upgrader.php
index 7acbaaed49..2d3c4cbb85 100644
--- src/wp-admin/includes/class-core-upgrader.php
+++ src/wp-admin/includes/class-core-upgrader.php
@@ -153,6 +153,7 @@ class Core_Upgrader extends WP_Upgrader {
 			return $working_dir;
 		}
 
+/*
 		// Copy update-core.php from the new version into place.
 		if ( ! $wp_filesystem->copy( $working_dir . '/wordpress/wp-admin/includes/update-core.php', $wp_dir . 'wp-admin/includes/update-core.php', true ) ) {
 			$wp_filesystem->delete( $working_dir, true );
@@ -160,6 +161,7 @@ class Core_Upgrader extends WP_Upgrader {
 			return new WP_Error( 'copy_failed_for_update_core_file', __( 'The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.' ), 'wp-admin/includes/update-core.php' );
 		}
 		$wp_filesystem->chmod( $wp_dir . 'wp-admin/includes/update-core.php', FS_CHMOD_FILE );
+*/
 
 		wp_opcache_invalidate( ABSPATH . 'wp-admin/includes/update-core.php' );
 		require_once ABSPATH . 'wp-admin/includes/update-core.php';
diff --git src/wp-admin/includes/update-core.php src/wp-admin/includes/update-core.php
index 6d9d243ddd..9d0452dbcb 100644
--- src/wp-admin/includes/update-core.php
+++ src/wp-admin/includes/update-core.php
@@ -946,6 +946,15 @@ function update_core( $from, $to ) {
 	}
 
 	$wp_filesystem->chmod( $versions_file, FS_CHMOD_FILE );
+
+	/*
+	 * `wp_opcache_invalidate()` only exists in WordPress 5.5 or later,
+	 * so don't run it when upgrading from older versions.
+	 */
+	if ( function_exists( 'wp_opcache_invalidate' ) ) {
+		wp_opcache_invalidate( $versions_file );
+	}
+
 	require WP_CONTENT_DIR . '/upgrade/version-current.php';
 	$wp_filesystem->delete( $versions_file );
 
@@ -1117,6 +1126,14 @@ function update_core( $from, $to ) {
 			$result = new WP_Error( 'copy_failed_for_version_file', __( 'The update cannot be installed because we will be unable to copy some files. This is usually due to inconsistent file permissions.' ), 'wp-includes/version.php' );
 		}
 		$wp_filesystem->chmod( $to . 'wp-includes/version.php', FS_CHMOD_FILE );
+
+		/*
+		 * `wp_opcache_invalidate()` only exists in WordPress 5.5 or later,
+		 * so don't run it when upgrading from older versions.
+		 */
+		if ( function_exists( 'wp_opcache_invalidate' ) ) {
+			wp_opcache_invalidate( $to . 'wp-includes/version.php' );
+		}
 	}
 
 	// Check to make sure everything copied correctly, ignoring the contents of wp-content.
diff --git src/wp-includes/version.php src/wp-includes/version.php
index 566625f027..37d8cfba67 100644
--- src/wp-includes/version.php
+++ src/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.8-alpha-50427-src';
+$wp_version = '5.5-alpha-50427-src';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git tools/local-env/php-config.ini tools/local-env/php-config.ini
index 1f385e924c..d8aa4622d1 100644
--- tools/local-env/php-config.ini
+++ tools/local-env/php-config.ini
@@ -1,2 +1,4 @@
 upload_max_filesize = 1G
 post_max_size = 1G
+opcache.enable = 1
+opcache.validate_timestamps = 0