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The largest planned office to residential conversion in Boston is a Back Bay property that went to a foreclosure auction in April.

New York-based Vanbarton Group estimated the 11-story building at 31 St. James Ave. can accommodate up to 490 apartments. The 11-story building spans an entire block between Arlington and Berkeley streets, with narrow floor plates that appear to be compatible with conversion to residences.

The estimated project cost is $410 million, according to an application submitted by Vanbarton Group to participate in Boston’s office to residential conversion tax abatement program.

Approximately 380,000 square feet is available for residential conversions, according to the document.

Market-rate apartments would rent for $6.50 to $7.50 per square foot, Vanbarton Group estimated. That translates into monthly rent of approximately $5,400, based upon average unit sizes of 775 square feet.

The project would reserve 20 percent of the apartments as income-restricted, as required by Boston’s inclusionary development policy.

The property, previously owned by Capital Properties of New York, lost a major office tenant in WeWork as a casualty of the coworking provider’s downsizing, and went into special servicing in 2024. All of the remaining office tenants are expected to vacate within 12 months, according to the application.

Lender LNR Partners submitted the high bid of $95 million at an online foreclosure auction this spring and hired Eastdil Secured Savills to market the property.

Vanbarton Group has three residential conversions under way in New York City totaling 1,511 units, according to application materials.

Boston’s conversion program offers property tax abatements of 75 percent for 29 years to qualifying projects. Developers say they aren’t relying on any federal or state funding to subsidize the project cost.

The program has attracted applications for 2,331 housing units in 36 buildings. To date, 431 units are under construction or completed.