Apple describes what happens when you fold the iPhone Duo shut in a single phrase: layouts that adapt to open, closed and posed positions. That is the extent of the consumer-facing explanation, and it is the one piece of iOS behaviour that no other iPhone has ever needed.
Everything else on the subject sits on Apple’s developer pages, where the instruction to app makers is dynamic resizing and adaptive layouts. Nobody outside Apple has folded one of these phones mid-task, so what follows is only what Apple documents about the handover between a 7.6-inch screen and a 5.4-inch one.
Key facts on the Duo’s two-display handover
| Item | What Apple publishes |
|---|---|
| Apple’s consumer wording | Layouts adapt to open, closed and posed positions |
| Apple’s developer wording | Build apps with dynamic resizing and adaptive layouts |
| Multitasking | Split View, two apps side by side on the inner display |
| Guidance live now | “Designing for iPhone Duo” in the Human Interface Guidelines |
| Guidance still to come | “Preparing your app for iPhone Duo,” dated only to later this month |
| Display point sizes and API names | Not published |
| Chip | A20 Pro drives both displays |
| Version | Ships with iOS 27.1 |
What Apple actually says about layouts that adapt
Apple’s product page groups three things together: Split View, a reimagined StandBy, and layouts that respond to whether the phone is open, closed or posed. The press release for the Duo adds an upgraded StandBy, a redesigned Dynamic Island and a Call Context widget to that list.
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None of those lines describes a transition. Apple does not say whether an app you are using on the inner display reopens on the outer one, whether Split View collapses to a single app when you fold the phone, or whether video keeps playing through the change. It says the layout adapts, and stops.
The two screens an app has to fit
The one concrete thing Apple does publish is the geometry, and it is the reason the company keeps using the word adaptive. Both displays share the same aspect ratio, which is the detail that makes a single layout plausible across them.
| Specification | Inner display | Outer display |
|---|---|---|
| Size | 7.6-inch Super Retina XDR folding OLED | 5.4-inch Super Retina XDR OLED |
| Resolution | 1878 by 2670 pixels | 1398 by 2034 pixels |
| Pixel density | 430 ppi | 460 ppi |
| Refresh | ProMotion up to 120Hz, Always-On | ProMotion up to 120Hz, Always-On |
| Brightness | 1000 nits typical, 1600 peak HDR, 3000 peak outdoor | Same figures |
| Finish | Custom nano-texture | Ceramic Shield 2 front |
| Apple’s comparison | 50 percent larger than iPhone 18 Pro Max | More than 90 percent of the iPhone 18 Pro screen area |
Apple’s point is that the smaller screen is not a cut-down companion panel: it has more than 90 percent of the area of the iPhone 18 Pro display, so an app arriving there is arriving on a full-size iPhone screen.
What Apple tells developers instead
The developer page Apple published on September 9 is where the fold-state work is actually described, and it names six sessions. Two of them are about exactly this problem: “Strike a pose with adaptive layouts on iPhone Duo” and “Leverage multiple displays and scenes on iPhone Duo.” The other four cover design, preparation, raising the bar and camera experiences.
What is not there yet is the toolchain. The Xcode 27.1 beta with the SDKs needed to build and test for the Duo is listed as coming later this month, as is the written guide. Apple has not published the displays’ point sizes, the names of any new fold-state APIs, or a simulator date.
The battery rating that assumes you switch
Apple’s own battery figures concede that people will move between the two screens. The Duo is rated for up to 44 hours of video playback on the outer display and up to 31 hours on the inner one, and the up to 24 hours of mixed use figure assumes equal inner and outer display use.
Streamed video follows the same split, at up to 37 hours outer and up to 26 hours inner. In other words, the single number Apple leads with is built on an assumption about how often the layout changes hands.
What Apple has not said
- Whether an app continues on the other display when you open or close the phone, or restarts
- What happens to Split View when the phone is folded shut
- Whether apps that have not been updated are scaled, letterboxed or left as they are
- The point sizes, safe areas or fold-state APIs developers will work against
- When the Xcode 27.1 beta and the written guide arrive, beyond later this month
- Whether any of this behaviour can be configured in Settings
Apple’s developer sessions are live now, the Xcode 27.1 beta is dated only to later this month, and iOS 27 reaches other iPhones on Monday, September 14. iPhone Duo pre-orders open Friday, October 16, with the phone on sale Friday, October 23. Our event recap and Duo against the Pro Max comparison cover the hardware side.
