The most stunning second of the iPhone Duo makes me re-understand liquid glass.

After the launch of iPhone Duo, the wave of controversy has been far more divisive than expected. The comment section of APPSO is also on the verge of fierce debates.

But no matter what attitude people hold towards foldable screens, those who have watched the launch event can hardly ignore the animation effects demonstrated by iPhone Duo.

It has to be said that Apple has absolute mastery of software and hardware collaboration. Looking back at the overwhelming controversy when Liquid Glass was first released a year ago, one can't help but sigh: Apple, how far can your vision really reach.

Apple's Foldable iPhone, What Is Truly Folded Is iOS

Most of the large foldable phones in the past were designed around an intuitive logic: folded as a mobile phone, unfolded close to a tablet. After users unfold the device, the system re-judges the window size and screen orientation, and then decides to display the mobile phone interface or the large-screen interface.

Objectively speaking, it is unfair to generalize the foldable screen ecosystem of the Android camp as a simple "stretching".

After years of iteration, Android, Samsung and a growing number of foldable screen manufacturers have made great progress in application continuity, window scaling and fold posture support. Applications can maintain the running state between the inner and outer screens, and developers can also reorganize the interface for different sizes.

What really leads to the sense of fragmentation is that the inner and outer screens usually use completely different proportions and layout logic.

Since the outer screen is narrow and long while the inner screen is square, the application needs to readjust text line breaks, image cropping and navigation structure after unfolding. Even if the application state can be continued, users will still clearly feel the switch of interface modes.

To solve this problem, Apple has adopted another solution in screen geometry and layout.

In terms of hardware dimensions, iPhone Duo has a 5.4-inch outer screen and a 7.6-inch inner screen. The outer screen provides about 90% of the display area of iPhone 18 Pro, while the inner screen is about 50% larger than iPhone 18 Pro Max.

What is more noteworthy is the ratio of the two screens.

Calculated according to the public resolution, the ratio of the long side to the short side of the outer screen is about 1.46:1, and that of the inner screen is about 1.42:1, which means that the unfolded inner screen is approximately an enlarged version of the outer screen rotated 90 degrees.

Supported by this physical geometry, iOS 27 on iPhone Duo has thus formed an independent layout between the traditional iPhone and iPadOS.

The Dock is moved from the bottom of the screen to the right, the Dynamic Island is arranged vertically, and the status bar that originally occupied the top is compressed into a circular entry in the upper right corner.

This layout change brings several direct engineering and interaction results:

The first is the preservation of vertical space. When the control elements are stored on the side, the display area left in the center of the screen has a length-to-width ratio closer to that of the traditional bar mobile phone.

The objective result of this design is to lower the adaptation threshold for developers. By simply following the conventional Size Classes rules, it is possible to avoid the horizontal stretching deformation that often occurs when third-party applications are directly unfolded at the system mechanism level.

More importantly, Apple hopes to maintain the spatial continuity between the inner and outer screens as much as possible. When users unfold iPhone Duo from the home screen, most icons and interface elements will not suddenly change positions, and the system completes the morphological change mainly by expanding the available space.

Full-screen applications still need to rearrange content, but the system control area fixed on the right will remain in place as much as possible, making users feel that the same set of interfaces is being unfolded, rather than suddenly jumping from the mobile phone interface to another set of tablet interfaces.

Experience Link: https://www.apple.com/iphone-duo/

Although iPhone Duo has not been officially shipped yet, netizen @MalayVasa has used GPT-6 Astra to make a wallpaper preview tool according to the screen size and ratio announced on the official website.

Experience Link: https://duo-fold.vercel.app/

We also used it to make a custom APPSO version of the wallpaper. After uploading the image, you can simulate its display effect on the outer screen of Duo and the unfolded inner screen.

The second is the adjustment of grip interaction. Placing the control bar on the right allows high-frequency operations such as return, Dock switching, and search to be concentrated within the normal reach range of the right thumb, forming an operation closed loop with the side Touch ID.

After entering the 50/50 split-screen multi-task mode, the system will align the control bar of the left application to the left edge of the screen, so that the two independently running applications on the left and right can fit the operation radius of the fingers nearby.

However, at present, this set of design also has obvious boundaries.

The multi-tasking capability of iPhone Duo is still mainly based on dual-app split screen, supporting opening two apps or two windows of the same app at the same time, and saving commonly used combinations.

Compared with some Android foldable screens that can already run three split-screen apps and multiple floating windows, Apple's attitude towards multi-tasking at this stage is still quite restrained.

Even, Apple does not require developers to design fixed interfaces for different states such as closed, half-open, landscape, and portrait, but introduces highly flexible Arrangement Views.

The system will automatically judge whether the main view and the secondary view should adopt the layout of "Split" or "Overlay" according to the current available space.

According to official Apple information, iPhone Duo will be pre-installed with iOS 27.1 system directly when it goes on sale in October this year, which also indicates the release time node of the first major update of iOS 27.

iOS 27.1 further optimizes the space scheduling of the toolbar.

The newly added toolbarCompressionBehavior allows developers to determine the compression order when space is insufficient according to the application type: navigation applications such as podcasts prioritize compressing the toolbar and retain the bottom tab bar; games and creation tools prioritize retracting the tab bar and retain core operations.

Through visibilityPriority, developers can also set display priorities for buttons. Key operations such as "Compose" in Mail and "New" in Notes will be retained first, and secondary buttons will be moved to the Overflow Menu when space is insufficient.

Compared with adding a dedicated interface for foldable screens, this underlying design that solves problems at the HIG (Human Interface Guidelines) paradigm level directly sets the lower limit of the basic experience.

Apple has also divided the adaptation of third-party applications into three levels. Applications still developed based on iOS 26 and earlier versions can only run in compatibility mode and cannot make full use of the larger inner screen;

After upgrading to iOS 27 SDK, applications can at least rearrange according to the new system size rules; only applications that have completed adaptation for Duo can migrate the top toolbar to the side and dynamically change the interface according to the hinge state.

One of the key differences is that applications using Apple's standard navigation bar and toolbar naturally have lower adaptation costs, while a large number of social, banking and game applications with custom UI require developers to readjust the layout.

Apple will provide the Duo simulator in iOS 27.1 and the new version of Xcode, but most developers still cannot get access to the real device before the official launch, so it is almost unavoidable that a large number of applications in different adaptation stages appear in the early stage of release.

Considering that the full adaptation of third-party applications will take a longer time.

Even in the first few months, a third-party application that can make full use of the dual screens, half-fold state and vertical toolbar may still be a few cases worthy of special discussion.