When we switch a domain to mobile-first indexing, it will see an increase in Googlebot's crawling, while we update our index to your site's mobile version. Depending on the domain, this change can take some time. Afterwards, we'll still occasionally crawl with the traditional desktop Googlebot, but most crawling for Search will be done with our mobile smartphone user-agent. The exact user-agent name used will match the Chromium version used for rendering.
In Search Console, there are multiple ways to check for mobile-first indexing. The status is shown on the settings page, as well as in the URL Inspection Tool, when checking a specific URL with regards to its most recent crawling.
Our guidance on making all websites work well for mobile-first indexing continues to be relevant, for new and existing sites. In particular, we 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. It's good to double-check these when a website is launched or significantly redesigned. In the URL Testing Tools you can easily check both desktop and mobile versions directly. If you use other tools to analyze your website, such as crawlers or monitoring tools, use a mobile user-agent if you want to match what Google Search sees.
While we continue to support various ways of making mobile websites, we recommend responsive web design for new websites. We suggest not using separate mobile URLs (often called "m-dot") because of issues and confusion we've seen over the years, both from search engines and users.
Mobile-first indexing has come a long way. It's great to see how the web has evolved from desktop to mobile, and how webmasters have helped to allow crawling & indexing to match how users interact with the web! We appreciate all your work over the years, which has helped to make this transition fairly smooth. We’ll continue to monitor and evaluate these changes carefully. If you have any questions, please drop by our Webmaster forums or our public events.