Pinterest signed a massive office deal in San Francisco’s central South of Market district, following its filing last month for an initial public offering.

The tech company, whose users “pin” photos and web pages into collections for sharing, leased nearly 490,000 square feet at 88 Bluxome St., a 1-million-square-foot mixed-use project that will replace the San Francisco Tennis Club.

The new office, expected to open in 2022, will have space for more than 3,000 employees based on average occupancy standards. Pinterest declined to disclose its future hiring plans. The company has more than 1,600 employees globally.

The deal is the city’s largest since Facebook’s 755,900-square-foot lease at Park Tower last May, which set a record for the city’s biggest lease.

Pinterest’s deal marks the first office lease in the newly rezoned central SoMa district, where a new wave of projects are planned but have yet to be approved. Taller buildings are allowed in exchange for community benefits. The plan prompted lawsuits by opponents calling for more environmental studies and both shorter and taller projects.

Developer Alexandria Real Estate Equities plans to transform 88 Bluxome St. into offices, life science labs, light industrial workshops and retail. Its community benefits include an expansion of Gene Friend Recreation Center with two swimming pools, a new linear park along Bluxome Street, public art, and land for 90 affordable apartments.

Alexandria will build 12 underground tennis courts operated by the Bay Club after members of the existing tennis club called for a replacement.

The details 88 Bluxome will have a variety of uses. Office: 850,000 sq. ft. Tennis club: 120,000 sq. ft. Community center: 28,000 sq. ft. Retail/other: 26,600 sq. ft.

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“The community center that we’re building here is something that’s been needed for decades,” said Stephen Richardson, co-CEO of Alexandria.

Pinterest cited 88 Bluxome’s community benefits for its decision to expand into the project, which is near its South of Market headquarters on Brannan Street.

“We were drawn to this project specifically because of how open the space will be to our neighbors,” Charlie Hale, head of public policy and social impact at Pinterest, said in a statement. “We are thankful to be part of SoMa and continue to identify ways our spaces can reflect our commitment to the neighborhood.”

Pinterest currently leases over 300,000 square feet in multiple buildings on Brannan Street, according to brokerage data. The company said it will continue occupying those buildings.

Pinterest has over 250 million active monthly users and primarily relies on advertising to generate revenue. In 2017, it was valued by $12 billion in a private funding round, and could seek a similar or higher valuation from public-market investors.

The 88 Bluxome project could be approved by June and construction could start next year, said Terezia Nemeth, Alexandria senior vice president of real estate development and community relations. She said discussions were ongoing to resolve opposition and lawsuits surrounding the central SoMa plan.

The project will rise to 225 feet and includes two major structures — one dark and one light.

“It creates this balance, yin and yang, of two design elements that work together,” Nemeth said.

Pinterest’s deal is the second recent example of a major office lease signed before a San Francisco project is even approved. In November, Salesforce leased 325,000 square feet at 564 Howard St. The Transbay tower isn’t expected to open until 2023.

The scarcity of office space is pushing tenants to lease buildings years in advance, said Robert Sammons, Northwest regional research director at brokerage Cushman & Wakefield. The city’s office vacancy rate is below 5 percent, he said.

“I do think it speaks to the challenge in leasing big blocks of space in San Francisco today,” he said. “If tenants want to continue to grow in this market, they have to be much more strategic than ever before.”

Roland Li is a Chronicle staff writer. Email: roland.li@sfchronicle.com Twitter: @rolandlisf