* OpenAI targets up to $1 trillion valuation, IPO could come

as early as September, source says

* Rival Anthropic and SpaceX also pursue IPOs, intensifying

competition for investor capital

* Jury ruled against Elon Musk's lawsuit, removing legal

hurdle for OpenAI's IPO

(Adds chart on OpenAI's reported market cap)

By Manya Saini and Pritam Biswas

June 8 (Reuters) - OpenAI confidentially filed for a U.S.

initial public offering recently, the ChatGPT maker said on

Monday, joining rival Anthropic in a push toward a stock market

listing as it looks to tap into insatiable investor demand for

AI shares.

OpenAI did not disclose the size or terms of the offering,

and said a timeline has not yet been determined. "It may be a

while because there are things we want to do that are likely

easier as a private company," it said in a statement.

Reuters had reported that the AI giant is targeting a valuation

of up to $1 trillion in a stock market debut that could come as

early as September.

At that valuation, OpenAI would set the stage for a trio of

trillion-dollar-valuation companies debuting rapidly, which

together are seen as the most consequential test of investor

appetite for high-growth technology stocks in the last 10 years.

Elon Musk's SpaceX was the first off the block, filing for an

IPO that would rank as the largest in history if completed, with

the company pursuing a $75 billion offering at a $1.75 trillion

valuation.

Anthropic, the company behind the viral coding assistant Claude

Code, said on June 1 it had confidentially filed for a U.S.

initial public offering, weeks after raising $65 billion in a

funding round that valued it at $965 billion.

"OpenAI is keeping options open as Anthropic edged ahead

with its filing after a monster funding round," said Michael

Ashley Schulman, a partner at Cerity Partners.

On prediction markets, where traders wager on the outcome of

future events, most participants had expected OpenAI to file for

an IPO before Anthropic.

THE AI ERA

The IPOs of Anthropic and OpenAI would crystallize a

transformative period for the technology industry and global

markets, with artificial intelligence rapidly emerging as the

defining investment theme of the decade.

OpenAI said earlier this year that it was raising $110

billion at an $840 billion valuation from a roster of

heavyweight backers including SoftBank, Amazon ( AMZN )

and Nvidia ( NVDA ).

At the time, it also disclosed that ChatGPT had more than

900 million weekly active users and over 50 million consumer

subscribers.

The IPO filing follows OpenAI renegotiating its partnership with

Microsoft ( MSFT ), one of its earliest investors, which allowed

the AI pioneer to forge new partnerships with firms such as

Amazon.com ( AMZN ) and Alphabet's Google.

The Windows maker's early investment, totaling $13 billion

since 2019, ​helped pave the way for OpenAI's rapid rise and

powered growth at ‌Microsoft's Azure cloud-computing business.

In March, OpenAI said it was generating $2 billion in

monthly revenue and growing roughly four times faster than

companies that defined the internet and mobile eras, including

Alphabet and Meta.

That compares with about $1 billion in quarterly revenue at

the end of 2024.

OpenAI told investors during its most recent fundraising

round that it did not expect to be profitable until 2030,

according to a source familiar with the matter.

CHALLENGERS GAIN MOMENTUM

Yet the industry OpenAI launched has quickly become crowded

and investors are scrutinizing whether the AI sector's meteoric

rise can be sustained.

Anthropic has emerged as one of the biggest rivals, with

soaring demand for its Claude AI from software developers to

handle their computer programming, and some firms deploying its

top-shelf model Mythos to unearth vulnerabilities in their code.

While the blockbuster offerings could inject fresh momentum

into the U.S. IPO market, some bankers warn they might also soak

up capital that could otherwise flow to smaller deals.

"What OpenAI does not want is for the public market capital

to exhaust itself," said Gil Luria, managing director of D.A.

Davidson. "Not only are SpaceX and Anthropic ahead of it in line

to IPO, large public competitors could also raise tens of

billions of dollars each in public market secondary issuances,

as Google just completed last week."

Musk-led SpaceX goes public this week.

NONPROFIT ROOTS SPARK LEGAL DISPUTE

OpenAI was founded in 2015 as a research-focused nonprofit,

but created a for-profit arm four years later to help fund the

soaring costs of developing artificial intelligence systems.

Its unusual structure, which gave the nonprofit control over

the for-profit entity, came under intense scrutiny in late 2023

when CEO Sam Altman was briefly ousted before returning days

later after employees revolted.

In December 2024, OpenAI unveiled plans to overhaul its

structure by creating a public benefit corporation, saying the

move would help it raise far more capital while easing

restrictions imposed by its nonprofit parent.

OpenAI's overhaul quickly became controversial after sharp

criticism from its early backer, Musk, who later sued OpenAI and

accused Altman and other executives of turning the nonprofit

into a vehicle for private enrichment.

A U.S. jury in May ruled against Musk in his lawsuit, finding

the AI ​company not liable to the world's richest person for

having allegedly strayed from its original mission to benefit

humanity.

The unanimous verdict removed a key overhang on the IPO,

with analysts saying it cleared a major legal hurdle.