EWAVR

SpaceX said on Thursday that its stake in Elon Musk's The Boring Co. netted the company an investment gain of $561 million during the third quarter.

The gain accounted for more than half of SpaceX's "other income" in the period and boosted its net income, which landed at just over $4 billion, the company said in its quarterly financial filing with the Securities and Exchange Commission.

Created inside SpaceX in 2017 and spun out a year later, Boring Co. says its mission is to "revolutionize transportation" by creating underground tunnels with stations where passengers can board and exit. Last month, Boring Co. raised $3 billion at a $23 billion valuation, with backing from the United Arab Emirates and a roster of other longtime Musk supporters.

Boring Co. has announced about a dozen city projects, but its only tunnels currently open for public use are in Las Vegas, where passengers can travel in Tesla vehicles between the downtown convention center and various casino resorts using its Las Vegas Convention Center Loop.

In July of last year, Boring Co. struck a deal to build about 20 miles of tunnels in Nashville, Tennessee. The Music City Loop, as it's known, is being designed to carry paying passengers between downtown and the airport in Tesla vehicles. The fast-tracked project sparked a partisan feud when it was greenlit and has drawn new safety concerns over sinkhole risks this week.

In the UAE, Boring Co. plans to build over 150 kilometers (93 miles) of tunnels, including a project announced in February of last year, the Dubai Loop.

SpaceX also said in Thursday's filing that it purchased $151 million worth of Tesla's Megapack energy storage systems during the quarter. Musk said on SpaceX's earnings call on Tuesday that he thinks it would be a "good idea" for the two companies to merge, and said they've both created special committees to discuss a potential transaction.