Anthropic is assembling a million-square-foot headquarters in San Francisco's Financial District, a real estate bet that tells you more about the company's IPO ambitions than any investor deck.
The AI developer signed a lease for roughly 100,000 square feet at 400 Howard Street, spanning three floors in Foundry Square I, according to the San Francisco Business Times, citing sources with knowledge of the deal. That follows an earlier deal for the entire 420,000-square-foot, 25-story tower at 300 Howard, where Anthropic will consolidate its headquarters in phases next year. This summer, employees begin moving into 400 Howard in two stages, The Real Deal reported.
The more revealing fact is what happened at 500 Howard. In 2023, Anthropic subleased roughly 240,000 square feet from Slack, a common strategy for fast-growing startups that want flexibility without committing to a long-term master lease. In April 2026, it converted that arrangement into a direct lease with the building owner, shedding its subtenant status, the Business Times reported. The conversion matters because sublease terms can be terminated when a master lease expires; a direct lease cannot. For a company reportedly planning to go public by the end of 2026, locking in real estate on favorable terms before an IPO is standard housekeeping.
Anthropic now controls nearly 1 million square feet across three addresses in a four-block FiDi cluster: 500 Howard, 300 Howard, and 400 Howard. That footprint sits inside a broader pattern. CBRE projects that AI firms will quadruple their Bay Area office footprint from 5 million square feet to 21 million by 2030, adding more than 50,000 AI sector workers to the region. San Francisco's Financial District, hollowed out by remote work and now offering discounted rents compared to 2019, is the obvious place to absorb that growth.
The company has the headcount to justify the space. At the start of 2026, Anthropic employed more than 1,300 people in the Bay Area out of a total headcount of 2,500. The valuation has kept pace. In February 2026, the company's total value was placed at $380 billion, more than double the $183 billion valuation reported in September 2025. The 2023 Slack sublease was signed when Anthropic was a well-funded but unprofitable safety lab. The 2026 direct leases are being signed by one of the most valuable private companies in the world.
Foundry Square is not coincidental. The complex sits near Salesforce Park, the Moscone Center expansion, and the BART and Muni transit hub at Powell and Market. It is also four blocks from OpenAI's growing Mission Bay cluster, a geography that has quietly made Howard Street one of the densest concentrations of AI talent on the planet.
Whether that density survives the company's next chapter is the open question. Anthropic and OpenAI are both reportedly targeting end-of-year IPOs. A direct lease on nearly 1 million square feet is a credible signal that Anthropic, at least, is planning to be here for the long run.
400 Howard is owned by the State Teachers Retirement System of Ohio, which acquired the building in 2012. At one point, BlackRock occupied the entire structure, though it has since scaled back to roughly 240,000 square feet.
