SAN FRANCISCO — Artificial intelligence giant Anthropic filed papers Monday for what could be the biggest initial public offering of stock ever even as its top executive warns that advanced AI could pose an existential threat to humanity. The filing sets up the San Francisco company for a Wall Street debut next month, potentially eclipsing the SpaceX initial public offering in June that raised a record $86 billion. An Anthropic IPO would also put the company ahead of OpenAI in going public in what is expected to be a pair of blockbuster stock debuts for the rival AI labs. The filing comes weeks after CEO Dario Amodei argued in an essay for slowing the development of the most advanced AI models. An IPO could provide Anthropic with enormous resources to accelerate its expansion. The amount the company ultimately raises remains uncertain, as do its final valuation and offering price, but even at lower estimates, it would turn the five-year-old startup into one of the world’s most valuable companies and potentially boost the wealth of Amodei and his sister and co-founder, Daniela, by b