Over the course of October, storefronts will be moving to return a Sitemap Index by default when navigating to /xmlsitemap.php, the default sitemap route for storefronts. There will be separate sitemaps for different types of pages such as Product, Categories, and Web Content Pages.

This change is being made in order to support storefronts which may have more than 50,000 URLs, which is the limit of URLs-per-sitemap defined by the sitemap specification.

However, there are other benefits to using a sitemap index, as it may provide better visibility into the indexing status of your sitemaps in tools such as Google Webmaster Tools.