What does the 'Savings Plans - Unused' service represent? And why does it change as the current month progresses?
The "Savings Plan - Unused" cost in the Cost History report for previous months is the unused cost from no upfront portions of a Savings Plan. The service item, 'Savings Plan - Unused' within the current month, represents the monthly Savings Plan commitment that is yet to be apportioned to Compute Usage.
It is expected for this figure will reduce each day after nightly processing based on the consumption of Savings Plan credits to On-Demand Usage, which any remaining 'Savings Plan - Unused' at the end of the month representing wasted Savings Plan commitment.