The number of individuals in deme Y remained at 9261 until 3573.0 generations ago, at which time it changed to a new stable size of 4239.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 9261
        end_time: 3573.0
      - start_size: 4239
        end_time: 0