For $599, the new Disney Flex Passport will offer guests select days (currently 147) that are “good-to-go” during which they can access one or both theme parks. A limited numbers of days (15 during the holidays) are blocked out entirely. The remaining 229 days may be available to Flex Passport holders via a new reservations system.
Guests will choose an available date and theme park for their party up to 30 days in advance on days that reservations are required (blue days in the example above). Reservations are limited and Flex Passport holder may only hold two reservations days at a time. The number of reservations available each day is limited.
Here’s more about the new Disney Flex Passport:
The Disney Flex Passport will be available for the monthly payment plan for California residents. It also includes dining and merchandise discounts.
Source: Disney Parks Blog