Usage export shows the carry on each outbound traffic row
In GET /v1/usage/export, each sandbox egress row's outbound measurements now include carried: the fraction of a microdollar the row started from, carried in from earlier outbound traffic in the same month, in bytes times microdollars per decimal GB. The row's charge plus written_off_micros equals floor((carried + billable bytes × rate) / 1,000,000,000). Charges are unchanged.