Mobile-first indexing, will use mobile friendly sites as a reference point.
An official announmenment regarind Google’s mobile-first search index has been made. Sites that have been migrated to mobile-first indexing are being notified via Search Console, and significantly increased crawl rates from the Smartphone Googlebot can be expect.
This change is simply related to how the content is gathered for Google’s index, and will not have an impact site that have been migrated over sites that have not.
Google’s mobile-first search index
Since 2015, mobile-friendly content have been ranking higher in search results when the users were searching on a mobile device.
There will be no separate ‘mobile-first index’ different from the main index. All content will be part of the same index structure, but a mobile version will be used when possible.
Since there are now more searches being conducted on mobile devices than desktop browsers, this is a way for Google to ensure the majority of users find content that’s optimized for their screen. If a site does not have a mobile-friendly version then Google will still crawl and index the site as-is.