Rivian Automotive (RIVN 4.50%) reported some good news with its third-quarter earnings report last week, and its stock has been on a roll ever since. Up until Thursday, that is. The electric vehicle (EV) maker's shares are still up by about 6% over the past week, but that includes a drop of 5.9% as of 11:10 a.m. ET in Thursday's session.

That decline came after one widely followed Wall Street investor -- billionaire investor George Soros -- revealed he had sold his entire stake in Rivian.

Soros sells out

In its recently released Form 13F filing with the Securities and Exchange Commission (SEC), Soros Fund Management showed that during the third quarter, it sold all of the approximately 4.2 million shares of Rivian it had held in the prior quarter. Those shares would be worth about $67 million at the most recent stock price, representing about 1.1% of the fund's portfolio value.

Should you sell out too?

Investors should recognize that the filing only indicates what Soros' fund held as of the end of the third quarter. It isn't known if Soros and his team have bought back into Rivian since that time. Nor are fund managers required to offer their reasons for adding or subtracting stocks, so outsiders can only speculate about why the firm sold its stake.

It's certainly possible that Soros lost confidence in Rivian, which has been burning through cash as it works to build up its production and sales volumes. The third-quarter report it delivered last week did contain some positive news for investors, though.

The EV start-up increased its production volume projection for the full year. It also announced that it was making its commercial vans available to companies other than Amazon, which has a large multiyear contract to purchase them.

Yet it's still unclear whether this EV company will ever reach profitability. That's the big risk to holding Rivian shares. Investors need to decide for themselves if they have the patience and risk tolerance to wait several years to find out. It appears that Soros decided that type of investment wasn't for him.