Native Instruments has announced that the current versions of their software products are compatible with OS X 10.9 (Mavericks).
They are reporting an issue with their non-class-compliant audio interfaces (such as the Audio 4, Audio 9, S4 Mk I, Audio Kontrol 1, et al). According to the Native Instruments’ site:
“If such an NI audio interface is connected to a computer waking up from Sleep mode, the device will invariably produce chopped and distorted audio on both input and output connections, or no audio at all. To resolve the issue disconnect and reconnect the device to your computer or change a setting of the audio interface —- e.g., switching the samplerate. Native Instruments is currently conducting further systematic compatibility and performance tests with the release version of Mavericks, and will provide new information on this page as it becomes available.”