As part of the deal, Grab would raise between $3 billion and $4 billion in a so-called PIPE, a funding round that typically accompanies a SPAC merger, the people said. That amount could still change as Grab and Altimeter will start meeting with mutual funds and other potential investors soon, some of the people said.

The parties could announce the deal in the next few weeks, though the talks could still fall apart and Grab could revert to an earlier plan to stage a traditional initial public offering on a U.S. exchange this year.

Should they move forward with a SPAC deal, it would be the high-water mark in a recent explosion of such transactions, in which an empty shell raises money in an IPO with plans to later find one or more companies to merge with. In some cases, the SPAC ends up with only a small sliver of the newly public target.

The vehicles have caught fire in the last couple of years, with everyone from former baseball player Alex Rodriguez to ex-House Speaker Paul Ryan getting in on the action. They have helped break a bottleneck between the private and public markets as companies that were reluctant to go public line up to combine with SPACs, which offer in many cases a speedier route to a listing without costs and disclosure limitations that accompany traditional IPOs.

The biggest SPAC deal to date is United Wholesale Mortgage’s roughly $16 billion combination with Gores Holdings IV Inc., announced in September. The biggest one so far this year is electric-vehicle company Lucid Motors Inc.’s agreement last month to merge with Michael Klein’s

Churchill Capital Corp.

IV, a deal valued at nearly $12 billion, according to Dealogic.

So far this year, a record $70 billion-plus has been raised for SPACs, which account for more than 70% of all public stock sales, according to Dealogic. A slew of companies are in talks for a SPAC merger or already have agreed to one, including office-sharing firm WeWork, online photo-book maker Shutterfly Inc. and online lender Social Finance Inc.

In addition to ride-hailing, Grab, which traces its roots back to 2011, delivers restaurant, grocery and other items and provides digital financial services to merchants.

Its backers include

SoftBank Group Corp.

,

Uber Technologies Inc.

and

Toyota Motor Corp.

It was last publicly valued at around $15 billion in an October 2019 fundraising round, according to PitchBook.

Its valuation is on the rise as public investors pile into other ride-hailing and food-delivery companies. Uber’s shares have jumped sharply in the past several months, while

DoorDash Inc.

went public in December at a valuation far in excess of where it had raised money privately. The restaurant-delivery company now has a market capitalization of nearly $47 billion.

Altimeter’s SPACs—Altimeter Growth Corp. and Altimeter Growth Corp. 2—raised $450 million and $400 million in October and January IPOs, respectively. Altimeter Capital, of Menlo Park, Calif., has around $16 billion under management and primarily invests in technology companies.

The firm has racked up a string of successful investments and was one of the main participants in a January round of funding

Roblox Corp.

raised ahead of its IPO at $45 a share. In its debut Wednesday, shares of the videogame platform traded more than 50% above that level and continued rising Thursday.

SoftBank, which invested through its Vision Fund, is also poised to win big on Grab, just as another of its bets proves to be a gigantic winner: The Japanese technology-investing giant has now made roughly $25 billion on paper on its $2.7 billion investment in South Korean e-commerce company

Coupang Inc.,

which soared 41% in its trading debut Thursday.

Write to Maureen Farrell at maureen.farrell@wsj.com