In a landmark shift in the city's homelessness policy, the de Blasio administration has reached a deal with homeless advocates and City Council members to require certain developers receiving city funding to set aside 15 percent of their new rental units for homeless New Yorkers.

The bill, which was first reported by the New York Times, was the result of two days of intense negotiations around a plan introduced a year ago by Rafael Salamanca Jr., a councilmember from the Bronx.

Based on an analysis of six years of city development data, the Coalition for the Homeless has estimated that the legislation will produce approximately 1,000 new apartments for the homeless a year, adding to the 1,300 units that the city is currently building a year for the unsheltered population.

"This is historic," Salamanca told Gothamist in a phone interview on Thursday. "We’re going to change the lives of thousands and thousands of individuals."

In a statement, Jane Meyer, a spokesperson for Mayor Bill de Blasio, said, "This agreement will ensure it’s written into law that future administrations continue the progress we’ve made and homeless New Yorkers can rest assured we’re doing all we can to put a safe and stable roof over their heads.”

As of September, there were more than 62,000 who spent a night in a homeless shelter, up from 52,000 during the same period in 2013, prior to de Blasio's first term.

De Blasio's cooperation with the legislation is a significant turnaround for the mayor, who has been facing mounting pressure from homeless advocates and elected officials to build more housing for the homeless. According to Coalition for the Homeless, more than half of the projects in de Blasio's affordable housing plan for low-income people have no units reserved for the homeless.

In an op-ed published by Gothamist on Thursday, current and former homeless outreach workers wrote that the mayor’s "focus on 311s without new housing, in addition to the MTA plan [to add 500 new police officers], paints a dystopic portrait of a city administration that would rather move, harass, and disappear their homeless residents than house them. The solution is simple; make material investments in housing and outreach agencies."

Even though other cities like Boston have adopted housing mandates for the homeless, New York City housing officials had previously resisted such a policy, arguing that they needed flexibility to negotiate affordable housing with developers on a case by case basis.

The two sides were originally far apart. Salamanca's original bill, which had overwhelming City Council support, including that of Council Speaker Corey Johnson, sought to apply the 15 percent requirement to any new rental building with 15 or more units—and to developments that fell under preservation deals.

According to those at the bargaining table, the administration proposed that the 15 percent mandate instead be considered an annual average across developments, and that it apply to projects with 120 units and more.

Salamanca said that both conditions were non-starters for him and homeless advocates. The concept of using an average, he argued, would likely concentrate homeless housing in the poorest neighborhoods, something which he specifically wanted to avoid. From the beginning, he has insisted that the 15 percent threshold could be done for every project, and pointed to five developments in his own district that had willingly signed on.

Under the revised legislation, the 15 percent requirement will apply only to new rental projects with more than 40 units. In another concession, he and others agreed to leave out affordable units created under preservation agreements.

With a veto-proof majority of council members in support, the City Council could have elected to simply pass the bill into law. But ultimately, Salamanca said, "The administration had some valid points." He cited the cost of doing affordable housing projects in neighborhoods where land costs are prohibitively high. "The financing in these other parts of the city is much more complicated," he said.

Giselle Routhier, the policy director for the Coalition for the Homeless, described the legislation as doing exactly what she and other homeless advocates have been asking of de Blasio.

"It marries the mayor's housing plan and his homelessness plan, which before were two separate plans," she said.

All told, since de Blasio took office, the city has financed over 11,700 homes for formerly homeless New Yorkers. Routhier said by her rough calculations, had the legislation been in place six years ago, the city could have produced an additional 8,500 units of housing for the homeless.

"We could have had a lower shelter census than we do now," she said. "But it’s good that we’re doing it now. We can’t wait any longer."

At an unrelated press conference on Thursday just before the news of the housing plan broke, Mayor de Blasio defended his approach on homelessness when asked about the Gothamist op-ed, pointing to a reduction in street homelessness.

"If we're at 2,400 people against a backdrop of 3,500 to 4,000 people, according to the last HOPE count on the streets – if 2,200 have come in, in three years in, stayed in, that’s a really, really big story and it's a story of, bluntly, I don't see a lot of reporting on," the mayor said. "If the critics say, 'You have to do more,' I say, you are right critics. But if the critics are saying, 'Well, you can't possibly get people off the streets,' then how do they explain the 2,400 who have come off the streets?"

The bill is expected to pass as early as next week. The new rules will take effect in July 2020.