Multi-component (multi-K) strategies in 3D concrete printing (3DCP) introduce additional streams to control material behavior, yet their underlying process principles remain poorly understood. This paper presents a process-oriented perspective on multi-K 3DCP. The evolution of multi-K processes is first reviewed in terms of the injection strategy and system configuration. Building on these developments, a conceptual framework for multi-K systems is proposed, in which K is interpreted as an independently controllable material input stream (K-stream) defined by its functional role and temporal-spatial deployment during printing. Based on this framework, K-streams are classified according to rheology regulation, mechanical performance enhancement, density grading and local composition tailoring, architectural and aesthetic design, and emerging functional targets. The analysis further highlights recurring challenges related to system layout and hardware constraints, inline mixing and flow-induced material heterogeneity, physicochemical interactions between streams, process monitoring, and closed-loop control. Finally, future perspectives toward robust, scalable, and functionally controlled multi-K 3DCP are discussed.