Microsoft has released the developers build of Windows Phone 8.1 months before it is expected to be rolled out publicly.
It is strictly only available to the development community, but if you just cannot wait until the official final release hits your Windows Phone, you can actually download it and use it now. Personal assistant Cortana too.
You have to register as a developer at dev.windowsphone.com for the Windows Phone Preview. This can either be for free, if you're willing to sign up with App Studio and technically "start a new project", or you can pay $19 and set yourself up as a fully fledged app developer who "might" publish apps to the Windows Store.
Either of these routes will work and you'll be able to download Windows Phone 8.1 and any future updates. You can also even update your phone with the official patch when it is released later in the year.
Another way to get the update now is to "developer unlock" your phone by registering it as a development handset. This requires the use of developers tools and is actually more complicated than the previous two methods.
There are caveats to registering yourself as a developer and downloading the Windows Phone 8.1 update. You could be voiding the warranty on your device. And should you be using a Nokia handset, you'll lose any of the Nokia Lumia specific features that the manufacturer gives you.
Also, you cannot return to the previous build of Windows Phone 8. So it's a one way ride kind of affair.
Still, if you are itching to be ahead of the pack, these issues might not be important to you. Good luck.