Up until 534.892 generations ago, the count of Y deme was 9781. Following that period, it changed to 6895, where it has persisted until now.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 9781
        end_time: 534.892
      - start_size: 6895
        end_time: 0