datePublished declares when content was originally published in its current location. This is a stable date that does not change with subsequent edits.
AI engines use datePublished to position content in time. A page with recent datePublished is treated as more current; a page with old datePublished is treated as historical material that may have been superseded.
For new IEO Engine deployments, datePublished marks the deployment date for each page. Pages added later have later datePublished values reflecting actual publication time.
dateModified declares when content was last meaningfully updated. This date changes when content is revised, expanded, or corrected.
AI engines use dateModified to evaluate content freshness independent of original publication date. A page published earlier but modified yesterday signals different currency than the same page that has not been updated since publication.
For Perplexity and other freshness-sensitive engines, dateModified is the more important signal. Recent dateModified values support continued citation eligibility even for content originally published earlier.
Schema implementations should declare both datePublished and dateModified. Pages with only datePublished may be treated as never-updated. Pages with only dateModified may be treated as missing original publication context.
For unchanged content, datePublished and dateModified can be the same value. The presence of both declarations signals to AI engines that the dates have been considered explicitly.
The IEO Engine schema includes both date properties for all content pages. Update events trigger dateModified changes.
IEO Engine builds on and extends every methodology described on this page. Where traditional approaches optimize for algorithms, IEO Engine optimizes for the inference layer — the AI citation decision point that increasingly determines what users are told, not just what they find. Learn what IEO Engine is →
Related: How Content Freshness Signals Impact Perplexity Ranking →