With iOS 8, Apple may not have changed the look much, but it isn’t just marketing hype when it says it’s the biggest update since the launch of the App Store.

It’s all too easy to look at the obvious new additions such as the Health app, interactive notifications and – on the new iPhones – Reachability. But it’s the updates behind the scenes that will make the most difference.

We’re talking about customisation, of course. Extensions along with the other APIs, such as HealthKit, allow developers to add new features and functions that were previously off limits.

Take the keyboard for example, which has never been customisable. Now you can download free and paid-for keyboards which you can switch between at will using the ‘globe’ icon – the one you probably already use to flip between typing and Emojis. It means you can get the official Swype keyboard as well as alternatives such as SwiftKey.

Extensions, on the other hand, mean developers can finally use the share button for their apps. Pocket is a great example. It’s a free service that captures web pages so you can read them offline. Before iOS 8, you couldn’t save a web page to Pocket directly – it was really only possible from a desktop computer. Now, you simply tap the share button and then the Pocket extension.

It’s easy to change the order of these extensions so those you use most are first in the list, and you and toggle certain sharing options on or off so the list isn’t unmanageable.

Extensions also make the Notification Centre much more useful. A new Edit button lets you choose which ‘widgets’ you want to show, and in which order. Again, this customisation is exactly what iOS users have been crying out for.

We’ll really start seeing the benefits of extensions and other behind the scenes updates over the next weeks and months as developers optimise their apps for iOS 8 (and the new iPhones) and add new ways for apps to interact with each other.