Developing for iPhone Duo
It looks like Xcode 27.1 is needed to test the iPhone Duo resizability - and that hasn’t been uploaded yet.
Cupertino and Friends™️ dropped six new videos over developing, designing, and crafting great apps for the nascent device:
In the Duo dev video, they describe how text buttons can’t be moved to the new vertical sidebar, as opposed to icon buttons.
I wonder if that’s one of the reasons Liquid Glass pushed hard for icon buttons, even though these are harder to understand; they make the vertical layout possible at all.
Totally confusing to me how the toolbar is ordered completely different between both modes here.
I think the problem with the iPhone Duo for developers is mostly that it does not create any new opportunities in the form of a new market or a new audience.
Previously:
Update (2026-09-17): See also: Accidental Tech Podcast.
Previously:
Update (2026-09-18): Xcode 27.1 Beta (Hacker News) adds support for iPhone Duo, but:
StandBy is unavailable in the iPhone Duo Simulator runtime.
Running and debugging most app extensions is unavailable in the iPhone Duo Simulator runtime.
Update (2026-09-21): Léo Natan:
Apple writing example code in Objective C, in 2026. They are REALLY desperate for developers to support this device.
On iPhone Duo, navigation controls, toolbar actions, and tabs can move into a shared vertical bar along the edge of the display, leaving more vertical space for content. Apps built with the iOS 27.1 SDK get this adaptation through standard containers such as
NavigationStack,NavigationSplitView, andTabView. We continue to declare toolbar actions in their usual placements, and SwiftUI determines how to present them in the current context.
I was going through the iPhone Duo specs and realised the inner screen has a different pixel density to the outer screen. The inner 7.6-inch folding display runs at 1878×2670 and 430 ppi, while the outer 5.4-inch display runs at 1398×2034 and 460 ppi.
The iPhone Duo remains interesting, and is clearly a technical tour-de-force that is the outcome of deep thinking about what a foldable phone can be. But the things that sparkle in my mind when I consider it is just the details. They are very important details that yield a noticeably different product, but they are sprinkles on top of a downward slope in user interface design at Apple that does not care any longer about what users or developers want. All that's important is for this year's device to uproot fundamentals and demand that everyone conform to an arbitrary new intuition.
Update (2026-09-29): Craig Hockenberry:
I don’t remember seeing this mentioned anywhere, but you have to be careful about where you place your safe area constraints.
My first pass moved the constraints on scroll/collection views from the superview leading/trailing to the safe area leading/trailing.
[…]
But if you look at Settings and Safari - our only two examples of “what’s right”, you’ll see the scroll indicators are “outside” the navigation bar and hug the edge of the device bezel.
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Apple likes to claim that developers are freeloaders who need to pay 30% for access to their valuable APIs. Is Apple going to pay developers to support all of the new APIs for a great iPhone Duo experience, given that for most developers it's just a bunch of work that won't benefit the developer in terms of increased sales, but greatly benefits Apple?
Look, I like to point out things Apple (or any billion dollar capital company) does wrong. But how about something more constructive. Maybe start with this unattributed claim that "developers are freeloaders"? Please, any link can only help. As for the "need to pay 30% for access to their valuable APIs"? I know for a fact that this is false. I pay US$99 annually to Apple for this access (of course only the public ones) and they take 15% of my sales because I'm not making US$1,000,000 annually.
You hurt your own argument when these sorts of, well, details are either missing or flat out wrong.
Would be great for developers to grow a backbone and some solidarity and refuse to support Apple’s fancy new gadgets until Apple starts treating them as fundamentally important to the experience. The iPhone would be nothing without devs but I’m already seeing too many complain that they “have” to put in the work to support yet another Apple form factor for free for the privilege of paying Apple fees on the platform Apple controls. While being treated horribly by Apple
Developers don’t have to do what Apple wants them to do. They could kill the Duo by refusing to update apps for it. And they should. Use it as leverage in negotiating a better deal. They don’t have opportunities like this all that often
@Dave:
> Maybe start with this unattributed claim that
> "developers are freeloaders"? Please, any link
> can only help. As for the "need to pay 30% for
> access to their valuable APIs"?
In Epic Games v. Apple, Apple argued that mandatory in-app purchasing “prevents free riding on Apple’s intellectual property by developers, such as Epic."
@Manx and others, thing is it doesn't matter to Apple all that much what indie developers do.
All they really need for it to be a success is for Meta and TikTok and Snapchat to support it. And a few of the other companies they already made deals with. That covers it for 99% of their market. Just look at what they promote on the App Store.
It seems a big part of the problem with Apple developer relations is their hypocrisy about treating all developers the same. They clearly do not. They made it pretty clear with this announcement that these phones are for "content creators" and high fashion individuals.
Actually @Plume did help the argument. Some. I don't see a link for the quoted passage about Epic v Apple, but the tone sounds about right. Still, an actual link makes the point even more strong.
As for what @bart says, it's more of the same. I definitely agree that Apple (1) has terrible developer relations anymore, (2) do not treat all developers the same - it's pretty explicit that if you make higher sales (US$1,000,000 I think is still the threshold) - they'll take 30% and not 15%, and (3) indie developers are in the lower tier.
But until someone provides links to the rest (success for the hardware is dependent on content creators and high fashion individuals along with how they choose who they promote) I'll wait until a year after the October release for the consumers to decide if this device is a success or not. Speaking of, the consumer, isn't Apple also guilty of establishing tiers there too? Virtually every piece of hardware they presented (particularly the iPhones) have price increases that aren't for most consumers. I'm glad they kept the price of AirPod 5s the same - well at least the lowest end.
The only thing they have made pretty clear to me over the last few months are they are your basic publicly owned company. Profits, profit margins, shareholders... these all take priority over their target consumer.
> Developers don’t have to do what Apple wants them to do.
Most devs do what they are told (see SwiftUI). And that technology devs actually have the power to kill it. IOS devs in this situation are going to eat it b/c
people will upgrade old phones to it and it will be a success. People already upgrade their phones way more often than they need.
It’s a product people want.
Unlike vision pro - that was obviously something almost nobody was ever gonna buy.
Unless they are going to separate iPhone apps, iPhone Duo apps, and iPad apps in the App Store, devs have existing products that are essentially going to be forced to support this so it isn’t like opting out is a real option if you want to be considered a serious iOS developer.
@Anonymous Yeah, Apple is using a pretty big stick—running unupdated apps in a little window—so I think there’s going to be a lot of pressure from users. The only way that wouldn’t happen is if iPhone Duo doesn’t sell, but I think it will.
> Unless they are going to separate iPhone apps, iPhone Duo apps, and iPad apps in the App Store, devs have existing products that are essentially going to be forced to support this so it isn’t like opting out is a real option if you want to be considered a serious iOS developer.
Considered serious iOS developer by whom? The iOS dev community which has no spin and drinks Apple koolaid like true believers? Ho no. That would be a shame.
Reality is that most devs could easily pass on the iPhone DUO unless its market share reach at least 10% which I doubt. The game industry understood this long ago, they always target the base iPhone specs. Most of the latests features and hardware are mostly never optimized for until the tech makes it to the baseline. Easy to see with most Pro line with Apple. I remember when COD mobile was running at 60fps on the latest iPhone / iPad Pros. The only device running at 120fps was an XPERIA… because SONY paid them to optimize the game for their phone as a marketing event. Apple’s hardware was far ahead in terms of perf, yet they didn’t let the game run above 60fps. Very smart move from the devs “we won’t support specifically your shiny high margin hardware until there is something for us”
Reality is that depending on how buggy and badly designed are APIs, it might cost more for devs to support the Duo than the money they will get back knowing they can’t charge more. Apple rips all the benefits, you work for free and on top of this you pay $99/y for the “privilege” to access their crap stack with xcode and swift getting worst every release and they tax you 15/30%. Such a treat.
