Oh, sorry about that.
It's the "64-bit Transition Guide for Cocoa Touch" on their developer site, so lots of pages of recommendations on how to approach your iOS 64-bit code if you're a developer. Note, I'm not actually a developer, but the basic registration is free, so I registered years ago.
The intro page is below:
---
About 64-Bit Cocoa Touch Apps
When desktop operating systems transitioned from 32-bit to 64-bit addressing, 64-bit apps were critical to the OS transition. Now, iOS is getting a similar desktop-class architecture. Starting with iOS 7, you can build iOS apps that take advantage of 64-bit processors. An app that supports 64-bit processing almost always gains improved performance when compared with a 32-bit app running on the same device.
At a Glance
Among other architecture improvements, a 64-bit ARM processor includes twice as many integer and floating-point registers as earlier processors do. As a result, 64-bit apps can work with more data at once for improved performance. Apps that extensively use 64-bit integer math or custom NEON operations see even larger performance gains. In a 64-bit process, pointers are 64 bits and some integer types, once 32 bits, are now 64 bits. Many data types in system frameworks, especially UIKit and Foundation, have also changed. Generally, 64-bit apps run more quickly and efficiently than their 32-bit equivalents. However, the transition to 64-bit code brings with it increased memory usage. If not managed carefully, the increased memory consumption can be detrimental to an app’s performance.
Convert Your App to a 64-Bit Binary After Updating It for iOS 7
Xcode can build your app with both 32-bit and 64-bit binaries included. This combined binary requires a minimum deployment target of iOS 6 or later. The 64-bit binary runs only on iOS 7 or later. If you have an existing app, you should first update your app for iOS 7 and then port it to run on 64-bit processors. By updating it first for iOS 7, you can remove deprecated code paths and use modern practices. If you are creating a new app, target iOS 7 and compile 32-bit and 64-bit versions of your app.
When iOS is executing on a 64-bit device, iOS includes separate 32-bit and 64-bit versions of the system frameworks. When all apps running on the device are compiled for the 64-bit runtime, iOS never loads the 32-bit versions of those libraries, which means that the system uses less memory and launches apps more quickly. Because all of the built-in apps already support the 64-bit runtime, it is to everyone’s benefit that all apps running on 64-bit devices be compiled for the 64-bit runtime, especially apps that support background processing. Even apps that are not performance sensitive gain from this memory efficiency.
Convert and Then Test Your App
The architecture for 64-bit apps on iOS is almost identical to the architecture for OS X apps, making it easy to create a common code base that runs in both operating systems. Converting a Cocoa Touch app to 64-bit follows a similar transition process as the one for Cocoa apps on OS X. Pointers and some common C types change from 32 bits to 64 bits. Code that relies on the NSInteger and CGFloat types needs to be carefully examined.
Start by building the app for the 64-bit runtime, fixing any warnings that occur as well as searching your code for specific 64-bit issues. For example:
Make sure all function calls have a proper prototype.
Avoid truncating 64-bit values by accidentally assigning them to a 32-bit data type.
Ensure that calculations are performed correctly in the 64-bit version of your app.
Create data structures whose layouts are identical in the 32-bit and 64-bit versions of your app (such as when you write a data file to iCloud).
Test your app on a 64-bit iOS device because some changes can be detected only when running on actual hardware. When your app is running, profile its performance and memory usage, improving both as necessary.
---
I find it interesting that they specifically comment about having 64-bit iOS makes it easier to have a common code base between iOS and OS X. Others have mentioned it here of course before, but the fact that they emphasize it somewhat suggests to me that Apple intends to transition quickly, like they did on OS X. At one key transition point, every iPhone and iPad and iPod touch that is not 64-bit will no longer be supported for new versions of iOS, regardless of the rest of its hardware. I could see this happening as early as 2016.