One of the key features of the Nexus One has nothing to do with its hardware. The latest and greatest Android phone also is the first device to come with the new Android 2.1 OS. And while other phones, like the Droid, are going to get it too (likely later this month), for now, if you want to play around with it, you’ll need a Nexus One. Or, starting today, you can also download the Android 2.1 SDK.

As noted on the Android Developers Blog, the team is releasing it before most devices have it so that developers can play around with and build for the new features introduced in 2.1. Though Google calls 2.1 a “minor platform release” over Android 2.0, there are a number of new elements such as voice recognition, live wallpapers, a new launcher, more home screens, and some WebKit changes. Those who have ported it over to the Droid note that the new OS is also faster.

Google also notes that there is a new USB manager available through the SDK Manager that supports the Nexus One. This may or may not be related to the new services that it seems like Google wants to include with the device, such as a new docking station for backing up your data.

You can find the new SDK here.