Last December after a year of testing, Google announced that its mobile-first indexing of Search results was underway to better reflect how many people use the web. Today, it is officially rolling out, beginning by “migrating sites that follow the best practices.”
Historically, Google’s crawling, indexing, and ranking systems analyzed the desktop version of a page. That is problematic given how the full version of a site might be “vastly different” from the mobile counterpart with content parity not maintained.
The solution is mobile-first indexing that uses content from the mobile version of the site, thus better reflecting the primary way people search for things today. This change does not mean that Google is maintaining separate indexes for desktop and mobile.
We continue to have one single index that we use for serving search results. We do not have a “mobile-first index” that’s separate from our main index. Historically, the desktop version was indexed, but increasingly, we will be using the mobile versions of content.
As a result of these changes, end users might encounter the mobile version of pages in Search results and Google cached pages.
Meanwhile, Google is now notifying sites that are being migrated over to mobile-first indexing in the Search Console, with site owners seeing a significantly increased crawl rate from the Smartphone Googlebot. In regards to Accelerated Mobile Pages, “Google will prefer to index the mobile version of the non-AMP page.”
The initial wave of mobile-first indexed sites will have “no ranking advantage over mobile content that’s not yet gathered this way or desktop content.” However, Google is encouraging that sites transition to mobile-friendly versions. It announced earlier this year that speed will become a factor to how mobile Search results are ranked, starting in July.