Most sites shown in search results are good to go for mobile-first indexing, and 70% of those shown in our search results have already shifted over.
Google will be switching to mobile-first indexing for all websites starting September 2020. In the meantime, they continue moving sites to mobile-first indexing when their systems recognize that they’re ready.
Most crawling for Search will be done with mobile smartphone user-agent. The exact user-agent name used will match the Chromium version used for rendering.
Google guidance on making all websites work well for mobile-first indexing continues to be relevant, for new and existing sites. In particular, they recommend making sure that the content shown is the same (including text, images, videos, links), and that meta data (titles and descriptions, robots meta tags) and all structured data is the same.