Rivian and Volkswagen Group have finalized a multi-billion-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.

Rivian Automotive shares soared Wednesday, a day after the electric vehicle manufacturer expanded its partnership with Volkswagen in a move aimed at helping both firms find ways to grab more of the market for EVs.

The new agreement, which builds on an earlier announcement, calls for the German automaker to invest $5.8 billion in Rivian, a maker of electric vehicles.