C4 model is a lean graphical notation technique for modelling the architecture of software systems. It is based on a structural decomposition of a system into containers and components and relies on existing modelling techniques such as the Unified Modelling Language (UML) or Entity Relation Diagrams (ERD) for the more detailed decomposition of the architectural building blocks.

C4 Provides a way to visualize different levels of abstraction so that a complex system can be discussed at different levels without requiring all participants to be familiar with the details of every level of the system.

C4 Diagrams should be refined and iterated on during each options pivot and as part of the learning portion of the delivery loop. If the C4 diagrams are regularly updated, it makes it faster and simpler to onboard new developers, achieve shared understanding across different delivery teams, and allows for simpler status reporting to stakeholders