Elon Musk just hit Sam Altman with an $800 billion counterpunch

• OpenAI overtook SpaceX as the world's most valuable private company in October.
• Now, a secondary share sale could catapult SpaceX back into the top spot — by a long shot.
• It's the latest turn in the long-running rivalry between Elon Musk and Sam Altman.

If Elon Musk and Sam Altman like each other, they hide it well.

In the latest turn in the rivalry, the two are battling over the top spot on the list of the world's most valuable private companies.

While the two cofounded OpenAI together back in 2015, the partnership has frayed spectacularly since.

Musk left OpenAI in 2018 and later founded rival startup, xAI. Musk or his company, xAI, has filed lawsuits against OpenAI.

OpenAI held a secondary share sale in October that valued it at $500 billion, taking the lead from Musk's SpaceX by a cool $100 billion.

Not one to cede ground to a rival, Musk is now planning his own secondary share sale at SpaceX, according to an internal letter to employees seen by multiple outlets. It would value the company at a whopping $800 billion. If that happens soon, it means Musk would have only let Altman hold the mantle for a couple of months.

Musk also confirmed on X this week that the company is exploring a blockbuster initial public offering, which might be the only way OpenAI can regain its lead as a private company. OpenAI this year restructured its business, which would allow it to also pursue its own eye-watering IPO in the future.

While this valuation battle between the two billionaires is maybe cringeworthy theater for the average earner, it underscores a significant shift: investors are pouring unprecedented money into technologies once viewed as speculative science projects.

SpaceX, which aims to make life multi-planetary and colonize Mars, and OpenAI, which seeks to develop a theoretical AI that can reason like humans, are two of the most visible examples, but they are part of a broader surge in frontier-tech valuations. AI, robotics, and defense tech startups have all notched multibillion-dollar valuations in the past year — bubble be damned.