An unprecedented Ga[GaH3]4 clusterion, with the neopentane structure, has been found in the solid state hydrides Rb8Ga5H15 and Cs8Ga5H15. This is the first gallium-hydrido cluster, with direct gallium-gallium bonds, forming a molecular structure of a common carbon-hydrogen compound. The discovery implies that further substitutions of hydrogen atoms with GaH3 units could be possible. This would open up for a new family of compounds with impact on hydrogen storage. The structural determination of the cluster showed extremely elongated temperature parameters for the terminal hydrogen atoms. This indicates a complex combination of distortions and dynamically vibrating atoms. Thus, the hydrogen dynamics represents a very important aspect of this compound. A precise spectroscopic characterization will be extremely useful for understanding the microscopic properties of these new materials.