The Reserved Capacity Contract That Priced Out Your Overflow When the Provider Redefined the Bucket
A platform team signed a multi-quarter reserved-throughput contract. Fixed per-token rate on committed capacity, a higher overage rate above the ceiling. Finance modeled the burn against six months of historical traffic that rarely crested the limit. The contract said "overflow" meant bytes-per-minute above the committed ceiling, and on that definition the deal was sound.
Six weeks later the bill was up 2.4× with no change to traffic shape, no change to routing config, no change to product surface. The provider had quietly revised the metering definition mid-quarter. "Overflow" now also counted any request the auto-router sent to a model tier above the one the reservation was anchored to — so a single Sonnet selection on a complex prompt landed in the overage bucket even when aggregate throughput sat comfortably inside the committed envelope. Thirty percent of traffic that used to invoice at the reserved rate now invoiced at the overage rate. Finance chased the spike through dashboards for three weeks before someone read the mid-quarter pricing addendum and found the redefinition in a footnote.
The contract had not been broken. The unit it was denominated in had been redenominated.
