Next month, Google will be changing the smartphone user-agent for Googlebot so its renderer can better understand pages that use newer web technologies.
Googlebot’s renderer evolves over time, the company says, and right now it renders pages more like Chrome than Safari. Changing the smartphone user-agent should have no affect on roughly 99% of sites.
The change will only have an affect on sites that specifically looks for a particular Googlebot user-agent string, which is not recommended in the first place. Implementing user-agent sniffing for Googlebot is considered to be a form of cloaking, whereas guidelines state Googlebot should be treated like any other browser.
Google’s Fetch and Render tool in Search Console has been updated with the new user-agent string. You’ll know for sure if your site is affected by the user-agent change by running it though that tool. You can also check by going into the Developer Tools on your browser and changing the user-agent string (for example, via Chrome Device Mode).