In this talk, I will present a novel approach based on a de Sitter S-matrix defined on an extended Poincaré patch to uncover new theories in de Sitter spacetime. By imposing a notion of Generalised Energy Conservation (GEC), we demonstrate that the four-point S-matrices for exceptional-series scalars in de Sitter spacetime are uniquely fixed. This framework naturally reproduces known theories such as Dirac–Born–Infeld (DBI) and the Special Galileon, while also providing evidence for the existence of new theories. Furthermore, we show that all exceptional theories exhibit a Universal Soft Behaviour (USB), arising from non-linear symmetries, which can likewise be used to uniquely fix the interactions. USB allows us to incorporate SU(N) Non-Linear Sigma Model to the catalogue of exceptional theories. Together, GEC and USB serve as unifying principles for the classification of exceptional theories in de Sitter spacetime.