Northampton or Somerville will take the final spot in a pilot program allowing a limited number of cities and towns to restrict fossil fuels in construction after a pair of other cities — including the state’s capital — opted to drop out of the running.

As many as four communities had once been in the mix to fill a single open slot in the program, but only Northampton and Somerville submitted official applications by last Friday deadline, according to the state Department of Energy Resources.

That means that neither Salem nor Boston will join the 10-municipality pilot program, despite each city previously approving a home rule petition seeking state permission to curb the use of fossil fuels locally.

It’s an about-face for Mayor Wu, who as recently as July 31 said her city was still hoping to join the program and needed state support to achieve Boston’s full climate goals.

Wu told the Boston Globe that she decided not to submit a formal application because she received “clear indications that Boston would not be chosen for the one available spot.”

The shift also reduces pressure on Gov. Healey’s administration, which gets to decide which “substitute community” will fill the final slot in the pilot program following West Tisbury’s withdrawal. Had officials selected Boston as the 10th community, they would have more than doubled the number of Massachusetts residents who live in participating cities and towns.

Lawmakers approved the pilot program in a 2022 clean energy law, aiming to get a better sense of the impacts of restricting fossil fuels in construction and major renovation. Buildings contributed about 35 percent of Massachusetts greenhouse gas emissions in 2020, the second-largest share of any individual sector.