Microsoft has removed the need to pay for Xbox Live Gold for free multiplayer games on Xbox One and Xbox Series X | S. The company announced this change at the beginning of the year, and until recently it was only available to some testers.
Effective April 21, all owners of current and previous generations of Microsoft consoles can play over 50 Free-to-Play games that support online multiplayer at no additional cost. You can find a complete list here. Paid projects still require a subscription.
As a reminder, on PlayStation consoles, a similar PlayStation Plus subscription is also not required for games distributed under the Free-to-Play model.