Examples relate to a hybrid model for case complexity classification. In an example, a set of fields corresponding to a case is received and the set of fields are inputted to a hybrid model comprising a set of rules and a predictive model. The predictive model includes a predictive machine learning model trained using a historical set of cases that are specific to a technical domain of the case. A case complexity classification for the case is determined via the hybrid model and based on analysis of the set of fields using the set of rules and the predictive model. The case complexity classification is utilized to route the case for processing.