Many moons ago, Google started offering a new “code-less” form of two-factor authentication. Instead of receiving a code in a text message, this sends a prompt to phones signed into your Google account so you can confirm that it is indeed you trying to log in. As of July 7th, this form of 2FA will be the default on Google and G Suite accounts.
Still, it won’t be the only option available—if you prefer SMS codes (which are inherently less secure, hence the change), you can revert back to that if you want. Otherwise, USB Security keys and whatnot will also continue to be supported. It’s also worth noting that if you’re currently using a security key, your 2FA method will not be switched to the phone prompt method, so you won’t have to do anything any differently.
This change will be on a slow rollout starting July 7th, and could take upwards of two weeks to be active on all accounts. One downside for people who already use code-less authentication is that it appears you’ll no longer have the option to disable prompts on specific phones. This is clearly a niche issues for users with multiple phones (like device reviewers, for example), so it probably won’t have a dramatic impact for most people, but it’s still worth noting.
Google via Engadget, Android Police