public interface KieSessionConfiguration extends PropertiesConfiguration, KieSessionOptionsConfigurationA class to store Session related configuration. It must be used at session instantiation time or not used at all. This class will automatically load default values from a number of places, accumulating properties from each location. This list of locations, in given priority is: System properties, home directory, working directory, META-INF/ of optionally provided classLoader META-INF/ of Thread.currentThread().getContextClassLoader() and META-INF/ of ClassLoader.getSystemClassLoader() So if you want to set a default configuration value for all your new KieSession, you can simply set the property as a System property. After the KieSession is created, it makes the configuration immutable and there is no way to make it mutable again. This is to avoid inconsistent behaviour inside KieSession.