wp-includes/sitemaps/class-wp-sitemaps-index.php:87Builds the URL for the sitemap index.
string public function get_index_url() { global $wp_rewrite; if ( ! $wp_rewrite->using_permalinks() ) { return home_url( '/?sitemap=index' ); } return home_url( '/wp-sitemap.xml' ); }Introduced in 5.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/sitemaps/class-wp-sitemaps-index.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.