The first oxygen–oxygen and neon–neon collisions at the LHC this July have opened a new frontier in exploring hot and dense QCD matter. These light-ion systems bridge the gap between proton–proton and heavy-ion collisions. Over the past decade, experiments have revealed intriguing but sometimes puzzling results: signals of elliptic flow appear even in proton–proton collisions, whereas clear signs of jet quenching remain absent in small systems. The recent pO, OO, and NeNe runs enable  precision tests of heavy-ion models in intermediate-size systems. Light-ion collisions probe the critical regime where nuclear structure, perturbative QCD, and quark–gluon plasma physics intersect. I will discuss what the first light-ion data reveal about the structure of the colliding nuclei, the applicability of hydrodynamics, and the onset of partonic energy loss in small systems.

This talk is part of the Light Ion Collision at LHC 2025 Workshop : https://indico.cern.ch/event/1597414