Phase diagram and assembly size distributions for different classes and assembly strengths. a Phase diagram as a function of ϕ tot and rescaled temperature T/T 0 (with T 0 = χ/k B ) in the regime of high assembly strength, i.e. − e int/χ ≫1. The green line is the volume fraction threshold ϕ ∗ (T ) at which intermediate-sized assemblies start to appear, which in this regime precedes the binodal (coloured curve). As indicated by the colour code, the monomer fraction ϕ 1 /ϕ tot mildly varies in the two phases. b Size distributions and c pictorial representations corresponding to different regions of the phase diagram, defined by the relative position of the binodal and the assembly threshold. In region “i”, the system is homogeneous and composed of monomers only. Increasing the total volume fraction of assemblies ϕ tot beyond the assembly threshold ϕ ∗ , the system enters region “ii” where intermediate assemblies appear. Here, the sizes corresponding to the maximum and the average of the distribution ϕ i scale with , see Appendix C . Finally, once ϕ tot exceeds the binodal, the system enters region “v” and demixes in two phases, both rich in intermediate assemblies. In d-f we focus on the low assembly strength regime, i.e. − e int/χ∼ 1. In phase diagram d , the binodal now precedes in ϕ tot the assembly threshold. e In region “iv”, the system phase separates but in both phases monomers dominate the size distribution, while in region “v” the dense phase becomes populated by intermediate-sized assemblies. Progressively lowering the temperature allows switching between these regions, as depicted in f. g ,h Behaviour of dilute mixtures as a function of assembly strength, for the two different classes. Notably, assembly below saturation becomes much more accessible for class 2, as can be seen by comparing the green regions “ii” in g and h .