Southwest periodically make flights for further in the future available. You can now book flights through April 24, 2022. Southwest has a good cancellation/refunds policy. You either get a credit towards a future flight (Wanna Get Away) or cash refund (Business Select or Anytime). That means it’s often a good idea to book as soon as the schedule is released and then check back to see if it has dropped in price, if/when it does you can just click ‘change flight’.