June 1 (Reuters) - AI giant Anthropic has confidentially filed for a U.S. initial public offering, the company said on Monday, edging ahead of rival OpenAI in a closely watched race to reach public markets.

The move sets up an early test of whether investor appetite for artificial intelligence, which has fueled lofty private valuations and talk of potential trillion-dollar listings, will hold up under public scrutiny, and which company gets to set the template for how the fast-growing sector is valued.

Anthropic, which makes agentic coding assistant Claude Code, did not disclose the size or the terms of the offering. It last raised $65 billion at a post-money valuation of $965 billion in late May, putting it ahead of OpenAI.

The listing would represent one of the most consequential stock market debuts in years, potentially reshaping benchmark indexes, investor flows and the broader narrative driving U.S. equities.

Reuters reported in May that OpenAI was also preparing to confidentially file for a U.S. IPO in the coming weeks. That follows SpaceX's mega-IPO filing, which is on course to rewrite the record books as the Elon Musk-led company pursues a $75 billion offering at a $1.75 trillion valuation and could begin trading within two weeks.

Confidential submissions let companies advance IPO preparations while shielding sensitive financial details from rivals and the public.

"Filing shortly after SpaceX allows Anthropic to capitalize on strong investor interest in AI and growth stocks while the window remains favorable," Kat Liu, vice president at IPO research firm IPOX, said.

"Anthropic's valuation ambitions appear far less aggressive in comparison (to SpaceX) than they might have looked in isolation."

RACE FOR AI DOMINANCE

OpenAI and Anthropic have become the face of the AI boom that has redrawn corporate strategies, sparked a global arms race for computing power and talent, and turned AI-linked companies into some of the market's most richly valued firms.

"For OpenAI, the conventional read is that Anthropic just seized the narrative advantage by filing first," said Harrison Rolfes, a senior analyst at PitchBook. "The unconventional read is that OpenAI got the better end of this: Anthropic just volunteered to absorb all the disclosure risk first, and OpenAI now has a free option to watch how institutional investors react to audited frontier AI financials before committing to its own price."

On prediction markets, where traders wager on the outcome of future events, most participants had expected OpenAI to file for an IPO before Anthropic.

Anthropic's valuation has more ​than doubled from $380 billion in February, when it raised $30 billion in a funding round.

The company's rapid rise in early 2026 rattled markets, triggering sharp selloffs in software and IT stocks as investors worried its increasingly autonomous AI tools could upend traditional business models and accelerate disruption across industries.

Its latest funding round drew backing from a mix of Silicon Valley and Wall Street investors, including Blackstone, Brookfield, D1 Capital Partners, GIC, General Catalyst and Insight Partners.

A MARKET MILESTONE

As a slew of blockbuster listings races toward public markets, companies from SpaceX to AI giants are competing for a finite pool of investor capital.

Analysts, including D.A. Davidson's Gil Luria, said the two companies were racing to go public before capital on Wall Street ran out, and to set the agenda for how a frontier AI model - one that pushes the boundaries of what machines can do in language, reasoning, or coding - reports financials in a way that is favorable to their financial model.

"The combined demand for capital from SpaceX, OpenAI and Anthropic will be so considerable that it is likely to create disruptions in the capital markets, so going early will be a great advantage," Luria said.

At a valuation of close to $1 trillion, Anthropic would vault to the top tier of the S&P 500, alongside a handful of elite companies that dominate global equity markets.

The IPO market has regained momentum in recent weeks, with companies raising $87.5 billion through May 26, the highest year-to-date global total since 2021, according to Dealogic data.

Several sizable U.S. IPOs are also set to hit the market later this week, including Honeywell-backed quantum computing firm Quantinuum, Blackstone-backed Liftoff and gas engine manufacturer Innio.