The station consists of a single island platform 410 feet (120 m) long, to handle up to 6 railcars on each side.

[3] Adding a commuter rail station at Assembly Square was listed as a possibility in 2012 as an interim air quality mitigation measure in response to delays building the Green Line Extension[7] However, such a station could not be completed by 2015, and the project was not supported by MassDOT.

[8] The area around the station formerly hosted a Ford automobile assembly plant, which used the adjacent Western Route for rail access.

[10] Somerville approved the project on May 2, 2011, and two days later the MBTA opened bidding for construction,[11] which was planned to start at the end of 2011.

[citation needed] The Assembly Square project is estimated to generate 45,000 new vehicle trips each day, and the station was intended to reduce the number that use private automobiles by diverting travelers to mass transit.

[19][2] The entire Orange Line, including Assembly station, was closed from August 19 to September 18, 2022, during maintenance work.

[20] A $49 million footbridge across the Mystic River between Assembly and the Encore Boston Harbor casino in Everett is planned.

By 2021, the project was to include an extension of the station's north headhouse to the east, with direct access from Draw 7 Park.

[24] Under draft plans released in 2008, the Urban Ring would have run on Grand Union Boulevard, with a stop at Foley Street about 800 feet (240 m) west of the Orange Line.