Tesla's investment bill ballooned in calendar Q2 as Elon Musk's biz entered what it calls its "largest and most exciting period of investment.

The company has poured resources into AI silicon and robotics, with capex [PDF] more than doubling from $2.5 billion in the previous quarter to $5.8 billion.

That left Tesla with negative free cash flow of $1.1 billion, down 848 percent year-on-year. It expects spending to keep rising and exceed $25 billion for the year.

During the earnings call, Musk talked up Tesla's Terafab ambitions but gave little detail other than calling it an "amazing initiative" and confirming that equipment orders had been placed for the development fab in Austin.

"It's intended to have lithography mask production, and then logic, memory and packaging, and chip testing all under one roof," he said. "So you can have a very fast iterative cycle." Musk acknowledged it was a "high-risk, high-payoff bet on AI chips."

Musk said Terafab was essential to scaling Optimus because Tesla would otherwise be unable to secure enough AI chips, hence the prodigious expenditure.

As for Tesla's automaker business, vehicle deliveries were up 25 percent year-on-year in Q2 to 480,126, and total automotive revenues surpassed $20 billion. However, operating margin fell to 1.4 percent from 4.1 percent a year ago.

According to Tesla, it is "in its largest and most exciting period of investment" as it builds out the infrastructure needed to make good on Musk's many promises.

"I think Optimus [Tesla's humanoid robot] will be the biggest product," Musk reiterated during the earnings call, before cautioning that "it is a very complex problem to solve."

Tesla is also facing stiff competition from China, which is also talking up its humanoid robots. Musk claimed Optimus will be the first "able to do generalized tasks."

Then there is the Robotaxi project, where the billionaire noted intense scrutiny from regulators "We're going as fast as humanly possible in scaling Robotaxi… while trying to ensure that we do not harm anyone at all and ideally do not even run over a pet," he said.

In answer to a question regarding combining Tesla and another of Musk's companies, SpaceX, he acknowledged overlap between the two but said it wasn't possible to talk about a combination on the Tesla results call.

He left it to Brandon Ehrhart, Tesla's general counsel, to say: "We continue to benefit from our relationship with SpaceX… They've been a great partner, and we have numerous beneficial transactions with them."

Investors were not impressed. Shares in the company fell in after-hours trading, while another of Musk's companies, SpaceX, continued its downward trajectory, standing at just over $115 by yesterday's close, well below its $135 IPO price and a huge drop from its $225 high. ®