That guarantee will not be available to new players: Those hired after July 1, 2020, will immediately move into the new plan, in which 7.5 percent of their base salary will be placed into retirement accounts.

The other major issue was wages. The new contract will include raises in each of the five years of the contract — of 2, 2, 2.5, 3.25 and 3.5 percent — which will bring the base salary to $181,272 in the final year, management said.

The strike attracted the attention of orchestras nationwide, which have been under pressure to curb expenses, especially during contract negotiations with their unions. While defined-benefit pensions have grown rarer in the private sector, they are still the norm among the nation’s leading orchestras. So musicians from around the country watched closely to see whether the Chicago players would succeed in protecting theirs.

The musicians’ union said in a statement that the new deal “preserves guaranteed minimum retirement benefits for current musicians and commits the parties to study options for providing retirement security for new hires.” In the past, unions have been loath to accept contract changes that would protect current workers at the expense of new hires, fearing that such deals would create two tiers of workers in the same orchestra.

The strike was also notable for the unusual involvement of the orchestra’s revered music director, Riccardo Muti, since conductors usually avoid seeming to take sides in labor disputes. But before the strike began, Mr. Muti wrote to the orchestra’s board and management, saying, “I am with the musicians,” and he later appeared with the players on the picket line.