Electric vehicle (EV) maker Rivian (NASDAQ: RIVN) said late Tuesday that it closed a hugely important deal, in which giant Volkswagen (OTC: VWAGY) will invest billions in the California-based upstart.

Volkswagen Group raised its investment in Rivian by 16% to $5.8 billion, the two automakers said on Tuesday, as the companies kick off their planned joint venture to develop electric vehicle architecture and software.

Rivian and Volkswagen Group have finalized a multibillion-dollar joint venture to develop software, paving the way to let the German auto giant leverage the EV startup’s more technical chops in the coming years. Volkswagen will invest up to $5.8 billion by 2027, about 16% more than when the deal was first announced in June.