The developer of Boston’s preferred site for a potential Amazon HQ2 is moving forward with its redevelopment plan months before a decision is expected from Seattle.

HYM Investment Group submitted a letter of intent to the Boston Planning and Development Agency Wednesday for its 11M SF plan to replace the Suffolk Downs horse track with a “new neighborhood with an active, lively and appropriate mix of uses.”

Submitting the letter officially launches BPDA review of the proposed redevelopment.

The development company bought the 161-acre race track in May for $155M, and its founding partner and managing director, Thomas O’Brien, indicated his company was pursuing a mix of ground-level retail and restaurants with housing above in the project’s early phases.

The letter to the BPDA indicates new retail squares at Beachmont Square and Belle Island Square, along with varied forms of housing, will be constructed. O’Brien said construction for the entire redevelopment will take place over a 15- to 20-year period.

Boston’s HQ2 bid dedicated a significant portion to Suffolk Downs and how its access to Logan International Airport and two on-site MBTA Blue Line stations made it the city’s best property for Amazon’s second headquarters.

HYM’s letter does not bring up the possibility of HQ2 until the end, when it indicates Amazon’s 500K SF space needs for the first phase of HQ2 might require expedited review and zoning changes to meet the company’s time frame.