The city has reached a deal with the largest union representing the Boston Police Department, the Herald has learned.

The city and the Boston Police Patrolmen’s Association have reached a breakthrough 5-year tentative contract deal that is pending ratification by the union members, according to a source familiar with the matter.

The union was not immediately available for comment or to provide further details. A release with more details is expected shortly from Mayor Michelle Wu’s office.

The basics of the deal include changes to arbitration rules, the detail system that has been under fire in recent months and “union retention time.”

This is a developing story.