Up until 9513.5 generations ago, the count of B deme was 2217. Following that period, it changed to 297, where it has persisted until now.
time_units: generations
demes:
  - name: B
    start_time: .inf
    epochs:
      - start_size: 2217
        end_time: 9513.5
      - start_size: 297
        end_time: 0