The formation of giant planets can mainly be explained by two models: core accretion and gravitational collapse. Measurements of magnetic and gravity fields, as well as deep composition can help to constrain which scenario led to the formation of the Solar System Giant Planets. The deep composition also holds keys to understanding how primordial ices condensed and trapped the heavy elements, in the form of pure condensates, amorphous ices or clathrates. While the Galileo probe enabled measuring the abundances of noble gases and other heavy elements in Jupiter, the elemental composition of Saturn and the Ice Giants remains poorly constrained. Observations coupled with thermochemical modeling can help us to constrain the deep composition of giant planets and can also be used in synergy with mass spectrometry measurements of an in situ probe.In this paper, we will present recent results of thermochemical modeling of the Ice Giants and compare them with results obtained for Jupiter.