As you use your phone to sign in to apps and sites and make purchases, your details can be saved to your Google account so they’re easily accessible from another device. Last year, Google added a security layer on top of these autofill prompts, to make sure only you can use your payment info and credentials. Now, a new setting allows you to sync those preferences across your devices.
The option should be available in Settings > Google > Autofill > Autofill with Google. The previous Autofill Security menu has been renamed to a more general Autofill Preferences, and you can see the new sync toggle there. Turning it on makes sure all your compatible devices follow the same setting, so you could force them all to require biometric identification before filling in your username and passwords and/or payment methods. If you’re more the lax type, you could also turn off the setting across all devices. And if Google ever adds more preferences in this section, the sync button will make sure all your devices follow whatever choice you make.
Left: Old settings. Right: New settings with sync.
The feature isn’t yet live for everyone — I don’t have it on my devices. It’s likely part of a server-side test in Google Play Services and will make its way to everyone soon enough.