Tesla CEO Elon Musk threw shade at Rivian on Thursday when he tweeted he hoped the automaker is able to “achieve high production and a breakeven cash flow,” and that accomplishing the feat would be “the true test.”

“There have been hundreds of automotive startups, both electric & combustion, but Tesla is [the] only American car maker to reach high volume production & positive cash flow in past 100 years,” Musk said on Twitter.

Rivian has 55,400 pre-orders for its R1S SUV and R1T pickup truck and a contract to build 100,000 cars with Amazon by 2030, according to the Wall Street Journal.

In its first two days of trading Rivian’s shares jumped 57% with a market value of more than $100 billion. Rivian began trading on Wednesday and closed 30% above its IPO price.

“We wanted to establish our brand by delivering a combination of efficiency, on-road performance, off-road capability, functional utility and product refinement that simply didn’t exist in the market,” Rivian CEO R.J. Scaringe told CNBC.

Rivian was founded in 2009 just six years after Tesla.

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