Up until 3120.27 generations ago, the count of Y deme was 2249. Following that period, it changed to 3526, where it has persisted until now.
time_units: generations
demes:
  - name: Y
    start_time: .inf
    epochs:
      - start_size: 2249
        end_time: 3120.27
      - start_size: 3526
        end_time: 0