Definition
lastmod is the XML sitemap element that declares when a page was last meaningfully updated. Search engines and AI crawlers use lastmod as a freshness signal to prioritize recrawling: a page whose lastmod moved recently is more likely to be refetched than a stale one. For GEO, accurate lastmod matters because AI engines prefer fresh content for time-sensitive queries — and incorrect lastmod (setting today's date on unchanged pages) erodes trust in your sitemap, causing engines to ignore the signal entirely. Google's documentation explicitly warns against updating lastmod without meaningful content changes. Best practice: update lastmod only when the page's substantive content changes (new data, revised conclusions, added sections), not for cosmetic edits (typo fixes, layout tweaks). Combine lastmod with IndexNow pings for Bing-indexed engines (Microsoft Copilot, ChatGPT search via Bing) to minimize the delay between publish and AI-citable. Automate lastmod in your CMS or build pipeline so it reflects actual content diffs.