iPhone Duo matches inner and outer display ratios, swaps Face ID for Touch ID

A user closes the Duo, reaches for the power button, and the phone wants a thumb rather than a look at the screen ^[4]. That is the smallest thing Apple changed in September and the first thing a real person will hit, because it is the only change that breaks a flow somebody already shipped and tested.

The pitch for a foldable is a bigger canvas. The work a foldable creates is mostly reflow, because the aspect ratio usually changes when the device opens and a second layout has to exist. Apple's answer is to keep the ratio the same inside and out, 5.4 inches on the outer display and 7.6 on the inner, which Macworld reports as apps flowing in and out ^[2]. If that holds, foldable support turns into a resize test rather than a design project. Apple's own description is the only evidence for it so far, and the announcement carried no developer detail ^[18].

Same gap on the camera. The headline change on the Pro is a variable aperture on the 48MP main wide camera, described as dynamically adjusting how much light the lens lets in for low light and bright light ^[10], on phones that otherwise look like last year's ^[14]. Nothing announced says whether an app can read that aperture or set it ^[18]. A capture pipeline rewritten this quarter is being built against a description of the resulting photo. Reviewers with test charts will characterise this lens long before any team gets a control surface for it.

The calendar is the part that can be planned against now. The Pro ships September 18 ^[13] and the Duo ships October 23 ^[3]: twelve days left in September plus twenty-three in October, so 35 days sit between the two waves ^[16]. One more number for whoever buys accessories: folded, the Duo measures 11.3mm against 5.2mm open ^[7], which leaves 0.9mm of hinge and air in the stack ^[17].

Two axes sort the backlog. The first is whether a flow assumes a face at the point of authentication. The second is whether it assumes a fixed window size at runtime. A flow that assumes neither needs nothing done to it. A flow that assumes a face needs a fingerprint path, on the most expensive iPhone in the range ^[4][3]. A flow that assumes a size needs a resize pass, because 5.4 inches and 7.6 inches are different amounts of room even at one ratio ^[2]. A flow that assumes both is where October goes.

Order those four by how loudly they fail. A layout that reflows badly gets a screenshot in a bug tracker; an unlock that never prompts gets a phone call from someone who just paid $1,999 ^[3] and cannot get into your app.