The breakthrough came at about 4 a.m., said Dan Totten, president of the Newspaper Guild. He did not release details pending a meeting with Guild members scheduled for Thursday.
"Out of respect for our members, the Guild and the New York Times Co. have agreed not to release details until Guild leaders have a chance to meet with our members," Totten said.
Globe spokesman Robert Powers said in a statement that details would not be released until Thursday. The Guild represents about 700 editorial, business and advertising staff.
The company had set a deadline of midnight Sunday to reach an agreement with its unions to make $20 million in cuts or close the Boston Globe. The Times Co. struck agreements with six of seven unions before the deadline, but even though talks with the Guild stalled, management backed off its threat to file a notice required by federal law to begin the process of shutting down the newspaper.
The two sides resumed talks Tuesday evening at a location outside Boston.
The Globe had proposed to slash wages by 23 percent to gain concessions of $10 million and keep the financially strapped newspaper from closing.
The Guild has offered a 3.5-percent pay cut, plus three unpaid furlough days, for a total salary reduction of just under 5 percent. It said its offer represents more than the $10 million in concessions sought.
The Times Co. also sought to change its lifetime job guarantees, a key sticking point. At least one of the smaller unions agreed to changes in the guarantees for its members, but Totten called ending that job protection a "nonstarter."
Nearly 470 employees across six unions have the guarantees, including about 190 Newspaper Guild members. Most got the promises in a contract ratified in 1994, shortly after the Times Co. bought the Globe for $1.1 billion, in exchange for other concessions at the time. Workers can still be fired for cause, but the newspaper says the guarantees reduce its ability to pare its operational structure.
The Times Co., which overall lost $74.5 million in the first quarter, has said that of all its newspaper properties, the Globe has been the most dramatically affected by the recession, the advertising downturn and the migration of readers online. The Globe had $50 million in operating losses in 2008 and is projected to lose $85 million this year.