From the page: > Yes. Two-factor authentication is a new service built directly into iOS 9 and OS X El Capitan. It uses different methods to trust devices and

From the page: > Yes. Two-factor authentication is a new service built directly into iOS 9 and OS X El Capitan. It uses different methods to trust devices and deliver verification codes, and offers a more streamlined user experience. Basically, it uses a (presumably) more secure method for handling verification. One benefit of this is OS X computers can now be trusted devices that display verification codes (Two-Step Authentication only allows iOS devices to be trusted devices)