SF’s AI office boom

San Francisco’s AI boom is no longer an abstract story about valuations and model releases. It is visible in floor plates, lease terms, and building addresses. In the first week of April, Anthropic converted its roughly 240,000-square-foot sublease at 500 Howard Street into a long-term direct lease, locking in one of downtown’s biggest AI office commitments. The company had first taken the former Slack space in 2023, when that deal was treated as a hopeful sign for a hollowed-out office core. Now it is a permanent one (bisnow.com) (therealdeal.com). That would already matter on its own. But Anthropic did not stop there. Days earlier, reports said it had leased another 100,000 square feet at 400 Howard Street, and earlier this year it took all 300 Howard Street, a deal reported at about 480,000 square feet including the adjacent smaller building on the parcel. Reuters, via Yahoo Finance, said the company plans to move its headquarters to 300 Howard next year and already occupies about 100,000 square feet at 505 Howard. Add it up and Anthropic has turned a few blocks of downtown into something close to a company campus without ever calling it one (therealdeal.com) (finance.yahoo.com) (therealdeal.com). That concentration is the real story. The post-pandemic office market was defined by dispersal. Companies shrank footprints, dumped space, and treated headquarters as optional. AI firms are doing the opposite. They are clustering teams in dense neighborhoods where engineers, founders, and investors can run into each other in person. San Francisco’s recovery is not broad. It is selective. A few fast-growing firms are taking premium space in a few favored districts, and that is enough to move market statistics because the blocks involved are so large (cbre.com) (ipgsf.com). Harvey shows the same pattern at a smaller scale. The legal-AI startup added two more floors at 201 Third Street in SoMa, bringing its footprint there to roughly 150,000 square feet. That expansion came less than a year after it first signed for about 93,000 square feet in the building. For Kilroy Realty, which has been dealing with vacancy, this is not just another tenant expansion. It is evidence that AI companies are not merely filling old offices. They are absorbing the exact kind of high-end downtown space that landlords have struggled to backfill since 2020 (therealdeal.com) (hoodline.com). The effect is now spilling south. The Mercury News reported that the South Bay just posted its strongest quarter for office leasing since the pandemic, helped by a surge in tech and AI demand. OpenAI signed a 450,000-square-foot lease in Mountain View in February, extending the same geography of concentration beyond San Francisco proper. This is what “AI cluster” means when it stops being a metaphor. It means one company takes a tower, another takes two floors, then another signs half a million square feet down the Peninsula, and suddenly a market that looked frozen starts moving again because a handful of firms want to sit near each other in real life (mercurynews.com) (therealdeal.com). It is tempting to call this a comeback for the whole office market. The data does not support that. San Francisco still has a huge amount of empty space, and even optimistic market reports describe the recovery as concentrated in top-tier buildings and a narrow set of tenants. What has changed is narrower and more interesting. AI companies are creating pockets of real density inside a still-fragile city center. In Anthropic’s case, that density now runs building to building along Howard Street, from 300 to 400 to 500 (ipgsf.com) (bisnow.com) (therealdeal.com).