S deme's population was steady at 4037 before it changed to 9216 2875.1 generations ago, maintaining that number to the present.
time_units: generations
demes:
  - name: S
    start_time: .inf
    epochs:
      - start_size: 4037
        end_time: 2875.1
      - start_size: 9216
        end_time: 0