To make sense of the acoustic environment, the auditory system must segregate, based on their history, streams of sounds arriving at the ear simultaneously. This requires sensitivity to both the probability and the predictability of the different sounds in the stream. That the auditory system is sensitive to the probability of appearance of a sound is well established. Here we presented complex sound sequences of varying predictability to anesthetized mice. Neuronal responses in the mouse inferior colliculus (IC) were recorded using Cambridge NeuroTech and Neuropixels probes. Neurons exhibited suppression that was specific to unpredictable sounds and could not be explained through tuning, probability of appearance, or adaptation triggered by the immediately preceding sounds. Notably, the magnitude of the suppression was dependent on the tuning of the neurons relative to the predictable sounds. Furthermore, the effect was insensitive to temporal expansions in the sound sequence resulting from increasing the inter-tone interval up to 4 times. Therefore, in complex auditory environments, neurons reflect unsupervised learning of the relative predictability of various sounds, in a process that might be relevant for stream segregation.