No, you cannot enter Disney California Adventure without a valid theme park reservation, even if you have a valid ticket or Magic Key pass. As of 2026, the Disneyland Resort continues to require all guests (age 3 and older) to make a reservation in advance to manage park capacity and staffing. If you have a Park Hopper ticket, you must make a reservation for your "starting park." After 11:00 AM, you can typically cross over to the other park without a second reservation, provided the park has not reached capacity. While reservations are generally easier to secure than in previous years, they can still sell out for popular dates like Christmas, spring break, or new attraction openings. It is highly recommended to check the Disney "Availability Calendar" before purchasing your ticket to ensure your desired dates are open.