Apple's second-generation iPhone Duo could gain Face ID, with prototypes already incorporating the technology beneath the outer display, according to Bloomberg's Mark Gurman.

In the latest episode of his "Power On" podcast, Gurman described Apple's work on adding facial authentication technology to its foldable iPhone. The company is said to be testing the hardware for a successor expected next fall, but has not finalized whether the feature will ship.

The current, first-generation ‌iPhone Duo‌ relies on a fingerprint sensor embedded in its side button, just like the iPad. Its thin design leaves limited space for the depth-sensing components needed for ‌Face ID‌.

News of the prototype seems to represent a more concrete development of Gurman's earlier prediction about future ‌iPhone Duo‌ upgrades. In September, he suggested that smaller components and advances in artificial intelligence could help Apple add ‌Face ID‌ and a dedicated telephoto camera by the third generation.

Gurman also said that Apple is considering adding an Action button to a future ‌iPhone Duo‌. The feature is noticeably lacking on the current model.

The first ‌iPhone Duo‌ launches tomorrow with a starting price of $1,999.