As you might know, Apple's Mac OS X 10.9 has just been released. Currently, we are testing all Steinberg products for OS X 10.9 compatibility. The testing is still going on, so we can't provide you with the final results.
However, what is known so far is that all Steinberg software products (except for Cubase LE / AI / Elements 7.0.6) are affected by an issue with the CoreAudio2ASIO component when using audio hardware in class-compliant mode which may lead to dangerous digital noise. Some Steinberg hardware products need to be updated as well to ensure full compatibility with the new OS X version. We therefore recommend you not to upgrade to OS X 10.9 yet.*
We are already working on updates for affected products in order to make them available as soon as possible. We will keep you up to date.
*In case you are using Cubase 7 and want to update to OS X 10.9 anyway, please make sure to deactivate the "Display have separate Spaces" option in the Mission Control Preferences.