Systems A–Si–H (A=Li, Na) have recently attracted attention since computational predictions suggested potentially superconducting and superionic hydrogen-rich ternary phases accessible at high pressures. As a characteristic feature, these A–Si–H phases are built from anionic hypervalent silicon-hydrogen species. Remarkably, their bonding properties relate closely to those of the recently discovered superconductors PH2 and H3S with Tc≤203 K. Such binary hydrides, however, are observed only at Mbar pressures. Anionic silicon-hydrogen species in A–Si–H phases may serve as recoverable proxies. Our earlier studies at ID06-LVP, ESRF revealed the compound Na3SiH7 accessible by hydrogenating NaH+Si mixtures at 5–9 GPa. To unfold formation conditions and phase relations of other predicted stable Na–Si–H phases containing hypervalent Si–H species, we propose expanding in situ hydrogenations at ID06-LVP by employing reactive precursor NaSi in reactions NaSi + NaH + H2 at p,T up to 10 GPa, 700°C.