WeWork continues its Boston growth trajectory with plans for an expansion to its Back Bay office.

A building permit was issued to WeWork by the city’s building department on May 11, according to BuildZoom. The permit shows the company is expanding its fourth floor presence at 31 St. James Ave. WeWork spokesperson Dominic McMullan said the company previously only had half of the fourth floor when it opened, and this permit is for build-out of the remainder. He declined to comment further on costs related to the expansion.

The co-working space operator originally signed a lease for 2.5 floors in the Park Square office building, its third Boston venue, in February of 2016. A year later, Amazon announced it would expand to the Back Bay location as it looked for a more permanent space outside of its office in Kendall Square. Recent reports indicate Amazon is close to a deal for an office at 253 Summer St. in Fort Point.