No - it just means new iOS apps must support 64-bit and be built with Xcode 6. Those same binaries/archives can also support 32-bit and older OS versions.
Similarly, today, you must build your app using at least the iOS 7 SDK and xcode 5, but that does not prevent you from supporting iOS 6 as well.
I read the link, I was focusing on the "built with the iOS 8 SDK" part. I'm asking the question whether or not building with the iOS 8 SDK would preclude that code from running on iOS 7 or is that only if that code uses iOS 8 features.
One reason is that, I believe, currently if even a single 32-bit app is loaded on a newer iOS device, all the standard 32-bit libraries have to be loaded into memory as well which causes increased memory pressure. This is a problem given that current iOS devices only have 1 GB of RAM. Getting older apps migrated to 64-bit is therefore a big deal for this reason alone.
I think HN has trained me to be very pessimistic about technology news. When I see a link posted like this without much commentary voted to the front page my first reaction is that it must be bad news.
If they only have a gig of RAM, why does iOS bother with 64-bit support at all? Doesn't that increase memory pressure due to all the pointers being twice as big?
Basically, as I understand it, 64-bit pointers on iOS can actually act to decrease memory pressure because the extra bits can be used to store object class information that would otherwise have to be stored separately.
This is important news for iOS developers as it means they must build and test their app on iOS 8, including any libraries that they use.
There are many ways and reasons why changing your build target may affect your app, so much so that's it's far beyond the scope of a hackernews thread. Supporting 64-bit, although introduced a while ago already with with iPhone 5S, can present some tricky bugs, also too much to explain here.
It's also meta-interesting as it shows the pace at which Apple wants app developers to adopt the new APIs, and will ultimately result in a more modern/ios 8 friendly app landscape.
EDIT: somebody else noted that you can likely still target earlier versions, which on the whole makes this much less interesting.
An app targeting iOS 7 built with an iOS 8 SDK may act very different from the same source built with an iOS 7 SDK. The modernization is mandatory and will definitively force apps to update to the new ways.
You can build against a higher SDK version than your minimum requirement with OS X/iOS. For example, your deployment target is OS X 10.7, but yo're building with the OS X 10.10 SDK.
