Originally, deme X had a population size of 2937, which changed to 8440 around 6364.82 generations ago and has not changed since.
time_units: generations
demes:
  - name: X
    start_time: .inf
    epochs:
      - start_size: 2937
        end_time: 6364.82
      - start_size: 8440
        end_time: 0