An Xbox Game Pass subscription is not necessary to play. Call of Duty: Warzone 2.0 falls under the free-to-play standards.

Yes, you can indeed play Warzone 3 for free. The new rendition remains free to play across all platforms, be it on PC or console. As mentioned, Warzone 3 will carry forward the entirety of the base game from Warzone 2 but will have new implementations that have been promised with the Modern Warfare 3 integration.