Until a shift occurred 4802.1 generations ago, deme Y's population was consistently 6452. Since then, it changed to 8579, a number that has remained unchanged to the current time.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 6452
        end_time: 4802.1
      - start_size: 8579
        end_time: 0