Larry Silverstein will celebrate the opening of 7 World Trade Center today with a ceremony and free concert in the small park adjacent to the new 52-story tower.

The concert, from noon to 2 p.m., is open to the public and will feature Lou Reed and Suzanne Vega, among others.

Mr. Silverstein has said the building will be full of tenants by this time next year. So far, less than 25% of the 1.7 million square feet of commercial space is spoken for.

Last week at a hearing about development at ground zero, Deputy Mayor Daniel Doctoroff said that Mr. Silverstein must be waiting for the downtown market to catch up with his asking prices, a subtle way of saying the building is overpriced. Mr. Silverstein is reportedly asking around $50 per square foot.

Mr. Silverstein started marketing the building in November, and since then Silverstein Properties, the New York Academy of Science, and Ameriprise, a financial services company, have each taken one floor. Negotiations are ongoing with the Beijing Vantone, a Chinese firm, to finalize a lease for the top five floors.

Part of Mr. Silverstein’s optimism comes from a growing spread between midtown and downtown rents, which is now reaching an all-time high, according to several commercial brokerages. For some class A office space, midtown rents are roughly twice as high as similar space in Lower Manhattan.

The president and CEO of GVA Williams, a commercial real estate brokerage, Robert Freedman, said that a short supply of high-end midtown space and high rents are making downtown more attractive.

“There is no question that trophy property downtown is starting to move very briskly,” Mr. Freedman.

Based on the building’s characteristics, Mr. Freedman said the 7 World Trade Center is the best office product downtown. But he said that commercial tenants moving to Lower Manhattan have to settle for two compromises: the amount of construction planned over the next five or six years, and the lack of transportation to the northern suburbs, like Westchester and Fairfield counties.

The leasing agent for 7 World Trade Center, Simon Wasserberger, of CB Richard Ellis, said that interest from prospective tenants has picked up since the latest agreement was signed between Mr. Silverstein and the Port Authority over ground zero, a 16-acre void adjacent to 7 World Trade Center.

Mr. Wasserberger would not name prospective tenants that have recently expressed interest in 7 World Trade Center.

The original 7 World Trade Center collapsed on September 11, 2001, from a fire caused by falling debris from the adjacent twin towers. The new building has been praised for its environmental sustainability and its sleek design.