According to a detailed support page, Apple is introducing a revamped two-factor authentication system with the third betas of iOS 9 and OS X 10.11 El Capitan.
The new two-factor authentication system is different from Apple’s existing two-step verification system, using different methods to trust devices and deliver verification codes. The company says that the system includes a more streamlined user experience.
Any device that you sign into using two-factor authentication in iOS 9 or OS X El Capitan becomes a trusted device that can be used to verify identity when signing into other devices or services linked to an Apple ID.
Apple recommends that iOS 9 and OS X El Capitan beta testers using the new two-factor authentication system should update all of their devices to iOS 9 and El Capitan for the best experience. Customers who use the new system with older devices may be required to use a six-digit verification code after entering their password instead of a dedicated verification field.
Older devices will not be able to receive two-factor authentication codes when used with devices running iOS 9 or El Capitan, but customers who stick with the old system should not run into any issues while Apple tests the new system. The company doesn’t recommend that users using the old two-factor verification system swap over to the new system until the feature is publicly available to all users.