Apple Inc's most important new phone for years will be called the iPhone X, according to a leak of the company's latest mobile operating system.

Strings of software code inside of the leaked operating system, first detailed by Apple news website 9to5Mac, show the expected three new phones will be called the iPhone 8, iPhone 8 Plus, and iPhone X. App and game developer Steven Troughton-Smith discovered the names in the software and tweeted about it on Saturday. 

The iPhone 8 and iPhone 8 Plus are successors to the current iPhone models, while the iPhone X is the premium version with an all-new design, crisper OLED screen, improved cameras, and a 3-D facial recognition scanner for unlocking the device.

The "X" in the iPhone's name may be a reference to this model being a special 10th anniversary edition. The iPhone 8 and iPhone 8 Plus will look similar to the iPhone 7 and iPhone 7 Plus, but include faster processors, Bloomberg News has reported. The new devices will be unveiled at an event on Tuesday. An Apple spokeswoman declined to comment.

The leak comes not long after Apple accidentally published early HomePod speaker software that provided details on upcoming iPhone features. Apple Chief Executive Officer Tim Cook has criticized news reports on upcoming iPhones this year, saying the articles dented sales of current models. Still, expectations are running high for a blockbuster holiday season: In a recent survey by RBC Capital Markets, almost two-thirds of respondents said they would buy a new iPhone model sight unseen.

The leaked operating system corroborates earlier reports that the premium X device will replace the usual Touch ID fingerprint scanner with a face unlock feature. Apple will call the enhancement Face ID, according to the code. The sensor will also be used for scanning a person's facial expression and converting that into animated emojis for messaging, the code shows. Bloomberg recently reported that the premium model will lack a home button and instead use a series of gestures for controlling the device.

The leaked software also sheds more light on an upcoming version of the Apple Watch that has its own cellular connection (existing models have to be tethered to an iPhone). 

The code also includes a photo of the new Watch, with a red button on the side and dots in the middle of the screen to show cellular signal strength. The image and the leaked code indicate the device will be capable of making phone calls without an iPhone in range and that Apple will announce new colours, including a grey ceramic and a new gold tone.