Valued Alibaba Cloud users:

Alibaba Cloud has optimized usage metering for pay-as-you-go NAT gateways. Starting February 5, 2021, if a NAT gateway consumes less than one capacity unit (CU) within a billing cycle (1 hour), the usage is no longer rounded up to one CU. Instead, the NAT gateway is charged based on the actual resources that are used. For more information, see Pay-by-data-transfer.