Microsoft's mysterious Surface Phone is still just a rumor, but new information has come to light.
Twitter user WalkingCat has spotted new APIs in the latest Windows 10 Test Build that indicate the phone will have a hinge. This means that much like phone-manufacturing giants Apple and Samsung, Microsoft may be entering the dual-screen phone war.
The APIs in question mention that the OS can respond to the "hinge state" of the device, and assign different values to Unknown, Closed, Concave, Flat, Convex and Full. Elsewhere in the code, tags including HingeAngleSensor and HingeAngleReading are mentioned.
This means that not only will the phone fold, but the phone's software will be aware of its position and respond accordingly. In tent mode, you could watch something at the same time as a friend from across the table, while in Concave mode, you could use the bottom screen to type like a keyboard on the top screen.
Motorola has patented a nifty system to prevent a foldable phone's display from creasing using heat. Meanwhile, Apple is working on a flexible battery cell that would fold up with the screen.
In May, an earlier Windows 10 build alluded to "Andromeda OS" and "Factory OS Andromeda Device." Andromeda is a code name that Microsoft attaches to new versions of Windows for specific devices, meaning this could be referring to a new OS for the Surface Phone. The code also contained Windows Core, a modular version of Windows that could incorporate cellular capability.
This is all speculative, but hopefully we'll find out more about this mysterious device in the coming months.