Having a model and being able to implement open-ended evolutionary systems are important for advancing our understanding of open-ended-ness. Complex systems science and the newest generation high-level programming languages provide intriguing possibilities to do so. Here, some recent advances in modeling and implementing open-ended evolutionary systems are reviewed (an earlier and shorter version was pre-sented at [1]). Then, the so-called allagmatic method is introduced as a computational framework that describes, models, implements and allows interpreting complex systems using system metamodeling. Based on recent advances, the model building blocks evolving entities, entity lifetime parameter, co-evolutionary operations of entities and environ-ment and combinatorial interactions are identified to characterize open-ended evolutionary systems. They are formalized within the system metamodel, providing a formal description of an open-ended evolutionary system. The study further provides a self-modifying code prototype in C# and guidance to create code blocks for an intrinsic implementation of open-ended evolutionary systems. This is achieved by control-ling the self-modification of program code within the abstractly defined building blocks of the system metamodel. It is concluded that the identified model building blocks and the proposed self-modifying code provide a promising starting point to model and implement open-ended-ness in a computational system that potentially allows us to interpret novelties at runtime. © 2024, Complex Systems Publications, Inc. All rights reserved.