Every second is its own settlement
Reserved capacity is billed and settled per second. Not per minute, not per
interval, not against a GB-second budget. At each second
t within an
interval:- if
usage(t) ≤ reservedGb: that second's memory is covered by your reservation and billed at the reserved rate - if
usage(t) > reservedGb: the part above the ceiling is overage, billed at the on-demand rate
Per 15-minute interval, per
(org, resource):text
12reservedBilled = reservedGb × 900 sec (the commitment, regardless of usage) overageBilled = ∑_t max(usage(t) − reservedGb, 0) (per-second integration)
Two charges, computed independently:
- Reserved: a flat
reservedGb × 900GB-seconds, billed every interval at the reserved rate, whether you used it or not. That's the commitment. - Overage: whatever exceeded the reserved ceiling at any instant, summed second by second, billed at the on-demand rate.
There is no draw-down, no carry-forward, no averaging. The ceiling is
re-checked every second.
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A worked example
You reserve 16 GB for
02:00–02:15. Your sandboxes use:| Phase | Duration | Memory |
| 1 | 600 s | 8 GB |
| 2 | 60 s | 30 GB |
| 3 | 240 s | 0 GB |
Each second is settled against the 16 GB ceiling:
| Phase | Reserved per s | Overage per s | Reserved GB·s | Overage GB·s |
| 1 | 8 | 0 | 4 800 | 0 |
| 2 | 16 | 14 | 960 | 840 |
| 3 | 0 | 0 | 0 | 0 |
Bill for the interval:
| Charge | GB-seconds | Rate |
| Reserved (commitment) | 14 400 | reserved |
| Overage | 840 | on-demand |
You pay the full 14 400 GB-seconds (
16 × 900) for the reservation
regardless of consumption. The 60-second spike to 30 GB produced 840
GB-seconds of overage on top, calculated second by second.Three contrasting cases
Usage stays below the ceiling. Reserve 16 GB, run 4 GB throughout.
Reserved = 14 400 GB·s (commitment, paid in full). Overage = 0. The unused
capacity is the cost of optionality you gave up.
Usage stays above the ceiling. Reserve 16 GB, run 24 GB throughout.
Reserved = 14 400 GB·s. Overage =
8 × 900 = 7 200 GB·s.Usage averages below the ceiling but spikes above. Reserve 16 GB, run
4 GB for 800 s then 25 GB for 100 s. Average is 6.8 GB — under
reservation. The 100 s above the ceiling still produces
9 × 100 = 900
GB·s of overage. The ceiling is checked every second; averages are
irrelevant.Reservation and overage are independent
| Question | Answer |
| Does the reservation amount affect the reserved bill? | Yes. Reserved bill = reservedGb × 900 per interval, always. |
| Does actual usage affect the reserved bill? | No. The commitment is paid in full regardless. |
| Does the reservation amount affect the overage bill? | Yes. Higher ceiling → less excess at each instant → less overage. |
| Does actual usage affect the overage bill? | Yes. Sum of seconds where usage exceeded the ceiling. |
| Do I get a credit for unused reserved capacity? | No. Unused reserved is the cost of commitment. |
Common confusions
"I'll only get overage when my total usage exceeds the GB-second budget."
There is no GB-second budget. Every second is settled independently
against the ceiling.
"I averaged less than my reservation, so there can't be overage."
Wrong if you ever exceeded the ceiling. Averaging is never applied.
"I didn't use my reservation; I shouldn't pay for it."
You pay for it because reserving means committing unconditionally. The
reserved rate is lower precisely because of that.
"My reservation should auto-cover spikes."
It doesn't. Spikes above the ceiling are overage. To cover spikes,
reserve a higher amount.
Edge cases
| Case | Behavior |
| You hold a reservation but run nothing | Reserved billed in full. No overage. |
| You run workloads but have no reservation | Ceiling is at zero. Every second of usage is overage. |
| You hold a reservation in one interval but run in another | No carryover. Allocation is per interval. |
| Multiple sandboxes' memory sums above the ceiling | Concurrent memory is summed before the ceiling is applied. No per-sandbox attribution. |
| A sandbox crashes mid-interval | Memory drops as soon as the scale event closes; subsequent seconds see the lower number. |
| You try to reserve for an interval you're already in | Rejected — reservations require a 30-minute minimum lead time. |
Why per-second
A GB-second budget would let arbitrary spikes ride for free as long as
quiet time balanced them out. That's burstable behavior, not
committed-capacity behavior, and it creates incentives for adversarial
spike patterns.
Per-second settlement matches what the reservation actually is: at every
moment, the ceiling is what you committed to. Above it is overage. Below
it is covered.