Bing updates sitemap rules, puts lastmod front and center for AI crawl
Bing just revised its sitemap guidance, zeroing in on the lastmod tag as key for AI-powered search crawling.
The issue started with how Bing’s AI indexes sites. Lastmod timestamps now help Bing decide which pages need recrawling—skipping stale ones to save resources. 
Details: Use strict ISO 8601 date+time for lastmod, like 2004-10-01T18:23:17+00:00. Don’t just slap on the sitemap generation time unless the page actually changed.
Changefreq and priority tags? Tossed. Bing no longer uses those for crawling or ranking.
Sitemaps can be submitted two ways: via robots.txt or Bing Webmaster Tools. Once submitted, Bing fetches immediately and checks daily.
Combine with IndexNow to get real-time URL-level updates alongside broad sitemap coverage.
Microsoft AI’s Fabrice Canel and Krishna Madhavan explain:
Bing says
the lastmod field in your sitemap is a top signal for AI-driven indexing. It helps determine whether a page needs to be recrawled or can be skipped.
By combining sitemaps for comprehensive site coverage with IndexNow for fast, URL-level submission, you provide the strongest foundation for keeping your content fresh, discoverable, and visible.
For huge sites, Bing supports massive scale: 50,000 URLs per sitemap, 50,000 sitemaps per index file, up to 2.5 trillion URLs overall.
Bottom line: accurate lastmod tags remain crucial as AI search evolves. Keep sitemaps clean and up to date for the best shot at being found.
Featured Image: PJ McDonnell/Shutterstock
