Rivian has completed winter testing for the VW ID.EVERY1, marking progress towards customer delivery and unlocking another $1 billion from Volkswagen Group. About $750 million will come as an equity investment while the remaining $250 million could be in the form of convertible debt, depending on which prototypes were tested.

The German automaker has already invested over $3 billion in Rivian through their joint venture and plans to lend up to another $1 billion starting in October. A further $460 million will follow once the first vehicle using joint venture technology goes on sale. All told, this could be worth as much as $5.8 billion to Rivian.

The milestone comes just months before Rivian launches the R2 SUV, which CEO RJ Scaringe describes as “maybe the most important thing we’ve launched to date.” With a focus on rapid scaling of production and sales, Rivian is hoping for a breakthrough in the electric vehicle market.