NORMAL, June 10 -- Rivian began delivering its R2 sport utility vehicle on Tuesday, the make-or-break model the loss-making startup is counting on to reach the scale that finally turns an electric-car company profitable. Built here alongside the pricier R1, the R2 opens near $58,000 and is meant to fall toward $45,000, offering more than 300 miles of range and aimed squarely at the Tesla Model Y. The first handovers, confirmed this week, pushed Rivian's stock up nearly 9 percent.

For Rivian, the milestone is real. Chief executive RJ Scaringe called the R2 the most important thing the company has launched, and the arithmetic behind it explains why. At full volume the SUV is expected to cost less than half as much to build as the R1, and t...