Yes. GTA VI allows the player to switch between Jason and Lucia while exploring the open world. Official extended footage also shows the two characters working together during story sequences, but it does not yet explain every restriction around switching.

The useful distinction is between the feature being confirmed and its full rules being known. GTA V provides a familiar comparison, although GTA VI is building around a romantic and criminal partnership rather than three largely separate lives.
What is confirmed
Jason and Lucia are both playable protagonists, and switching is available during open-world exploration. This means neither character is limited to cinematic appearances or a narrow set of isolated missions.
The footage presents switching as part of ordinary movement through Leonida, not only a scripted handoff. That is the clearest answer to the basic question players have been asking since the first trailer.
Can you switch during missions?
The footage shows Jason and Lucia occupying different roles during joint sequences, and reports around the official presentation describe switching within gameplay. The exact availability is likely to depend on the mission and the characters present.
It would be premature to claim that every mission permits switching at any moment. Story direction, location and mission failure rules can reasonably create restrictions even when the wider system is flexible.
How this may differ from GTA V
GTA V often used switching to move between three separate schedules, homes and criminal roles. GTA VI places one close relationship at the center, so a switch can change not only location but also responsibility inside the same plan.
That creates opportunities for coordinated jobs and consequences viewed from the other person's position. It may also make separation more meaningful when the story places tension between them.
What remains unknown
Rockstar has not published a complete switching interface guide, cooldown rules, mission list or explanation of what happens when one protagonist is far from the other.
Those details should be added after an unedited demonstration or support documentation appears. For now, the important answer is firm: both are playable, and open-world switching is part of GTA VI.
Sources checked