For more than two decades, putting a number on a Tesla-SpaceX merger was guesswork because only one of the two companies traded publicly. That changed on June 12, when SpaceX (SPCX +19.79%) completed the largest initial public offering (IPO) in history at a valuation near $1.8 trillion. With a public price finally attached to the rocket company, long-running speculation that Elon Musk will fold his two trillion-dollar businesses into one resurfaced.

The figures involved are enormous. Electric-car maker Tesla (TSLA +0.98%) carries a market capitalization of about $1.5 trillion as of this writing, while SpaceX rose above a $2 trillion market value in its first session. Put the two together, and you get a company worth more than $3 trillion — enough to rank among the four most valuable in the world.

Wedbush analyst Dan Ives recently put the odds of such a tie-up within a year at about 80%.

So what would a combination actually mean for the people who own Tesla today?

Here’s a closer look.

The case for a combination

The argument for merging starts with the extent of overlap between the two companies. Musk increasingly pitches Tesla as an artificial intelligence (AI) and robotics company — think self-driving software and the Optimus humanoid robot — even though most of its revenue still comes from selling cars. SpaceX brings satellite internet through Starlink and launch capacity, and its February acquisition of Musk’s AI start-up xAI added the Grok chatbot.

Ives frames a tie-up as Musk’s clearest path to controlling more of the AI ecosystem under one roof.

A path to a merger seems plausible. Tesla invested $2 billion in xAI in January. When SpaceX absorbed xAI a month later, that stake converted into nearly 19 million SpaceX shares, worth about $2.6 billion at the IPO price. And the two are also jointly building a chip-making plant in Austin, known as Terafab, meant to supply processors for Tesla’s robots and SpaceX’s satellites alike.

Additionally, a merger between the two companies could help settle the case once and for all that Tesla is more than just a car company. Rather than Tesla shareholders owning a car company trying to become an AI company, they would hold a slice of an operation spanning electric vehicles, robotics, rockets, satellite internet, and AI.

The bull case is essentially that the market would stop valuing Tesla mainly on its car sales and start treating it as one pillar of a multitrillion-dollar Musk empire.

Why it may not play out the way bulls hope

But SpaceX’s own leadership sounds far more measured than the headline odds.

“Right now I’m focused on keeping the lights on here,” said SpaceX president and chief operating officer Gwynne Shotwell in a CNBC interview on the day of the IPO. She allowed that the two businesses share long-term goals but stopped well short of calling a merger imminent.

The betting markets offer a more conservative view, too. As of this writing, prediction platforms put the near-term odds of a deal well below Ives’s 80% — in the range of 25% to 40% for a combination this year.

Additionally, there’s the issue of who would set the terms for such a merger. Musk holds more than 80% of the voting power at SpaceX through a dual-class share structure, yet he owns only about a fifth of Tesla. That gap matters. A merger would be a related-party transaction with Musk on both sides of the table, and any deal would almost certainly be built largely around the company he controls outright.

Space Exploration Technologies

Today’s Change

(19.79%) $31.85

Current Price

$192.80

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Market Cap

$2.5T

Day’s Range

$168.40 – $192.87

52wk Range

$135.00 – $193.00

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Then there’s price. Tesla shares trade at about 370 times earnings as of this writing, a valuation that already assumes the company will succeed in autonomy and robotics on its own. And a merger likely wouldn’t help. It would add SpaceX’s own unproven, money-losing space and AI ambitions to an already expensive stock.

So where does this leave Tesla investors? I think the honest answer is that a merger is a real possibility, but not a sure thing — and that the more important question isn’t whether it happens but on whose terms. Because Musk controls SpaceX and only a minority of Tesla, any combination would likely look less like a merger of equals and more like SpaceX absorbing Tesla.

Whatever the case, investors should make their investment decisions today based on each company’s underlying fundamentals relative to the price they are paying, not because of merger prospects. Because one thing is certain: It’s unclear what a merger or acquisition could look like, and under what terms it would happen.