The story 25 October 2026
Apple’s Folding Phone Arrives, and a Web Page Can Learn Where the Fold Is
iPhone Duo went on sale on Friday with Safari 27.1 on it. Held half open, like a book, its inner screen has two halves with the fold between them. A page can now ask the browser whether the phone is folded and how wide each half is, and put one column on each side, so that no photograph or line of text runs across the crease. Chrome on Android folding phones has done this since last year.
Laid out as one wide screen
When the browser reports the phone folded: one column each side
Apple’s first folding phone went on sale on Friday. Closed, iPhone Duo has a 5.4-inch screen on the front, like any phone. Opened, the inside unfolds to 7.6 inches. Held half open, like a book, that inner screen has a left half and a right half with the fold running between them. Safari 27.1 shipped with it; the WebKit team, which builds Safari, opens its notes for the release with “Today iPhone Duo arrives, and with it, Safari 27.1.”
Safari itself already uses the two halves. When the phone is half open, “Safari 27.1 automatically shows PDFs as two pages side by side,” one page to each half, like an open book. Web pages can now do the same. CSS, the language that sets how a page looks, has long let a page ask the browser a question about the screen, such as whether it is as narrow as a phone, and change its layout on the answer. The new question is called device-posture, and the answer is either folded or continuous, the standard’s word for flat. WebKit’s own example answers folded with two equal columns, each the width of one half of the screen, so that the fold falls in the gap between them and nothing is printed across it.
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A second set of measurements tells the page exactly where each half is. In WebKit’s words, “It describes the ‘segments’ of the display — the separate portions on either side of the fold.” Six values give the width, the height and the position of each half. A designer can put the photograph on the left half and the caption on the right, or the menu on one side and the article on the other, with the gutter set on the fold itself.
None of this is Apple’s alone. Both questions come from a draft web standard, the Device Posture API, whose current text at the W3C, the body that writes web standards, is dated May of this year. The draft says what it is for: “The main interest in knowing the posture of a device is to enable new user experiences with responsive design.” Chrome on Android folding phones has answered the posture question since early 2025 and reported the two halves since the middle of that year. Firefox does neither.
In Safari 27.1 the two questions are “a developer preview behind feature flags,” switched off until the owner of the phone turns them on in Settings. A site can be built and tested for the Duo today, but it cannot yet count on being told about the fold. What every site meets in the meantime is a very wide phone. A single Safari window on the Duo can be anywhere from 382 to 951 pixels across, depending on which screen is in use and how the phone is held, and the inner screen is treated as one wide screen with the crease running through the middle of whatever is on it.
Why it mattersFor the first time an iPhone can hold a web page open like a book, and a designer can decide what sits on each side. Few visitors will have one this year, and the fold is reported to a page only when the owner switches it on, so the habit to start now is simpler: at wide phone sizes, keep the headline, the face in the photograph and the button away from the middle of the screen, where the crease of a half-open Duo falls.
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Sources: WebKit: Features for Safari 27.1 (23 October 2026) · Apple Newsroom: iPhone Duo arrives at Apple Store locations worldwide · Apple Newsroom: Open up to new possibilities with iPhone Duo (display sizes) · W3C: Device Posture API (Candidate Recommendation Draft, May 2026) · MDN: device-posture media feature · Chrome for Developers: the Viewport Segments API shipped in Chrome 138 (June 2025) · MDN browser compatibility data: media features