Extensivity is an essential thermodynamic requirement which is usually broken for long-range correlated and non-exponential growth rate complex systems. The standard approach that deals with this issue is normalization of the system Hamiltonian by a quantity which explicitly depends on the system size (Kac's prescription). However, as noted by several authors, the prescription does not justify its use from the physical point of view.

In this talk we present an alternative approach based on physically consistent generalized thermostatistics which is defined from non-additive entropies and internal energies. The approach is applied for thermostatistical characterization of non-extensive traveling salesman problem. Possible applications to Currie-Weiss model, Sherington-Kirkpatrick model and Hamiltonian mean field model are also pointed out.