Spend ceilings and limits
What a FluxRouter spend ceiling is, which limits stop a request today, the basis each one is measured on, and how paid ceilings rise over time with cleared spend and account age.
A spend ceiling is a monthly runaway-cost limit on your account. It exists so that a loop, a leaked key or an over-eager script cannot quietly rack up a large bill before you notice.
This page describes what stops a request today, and on what basis. Where a limit does not currently apply to your account, it says so rather than describing an intention.
Which limits stop a request today
| limit | applies to | basis it is measured on | what you receive |
|---|---|---|---|
| Free plan $1 monthly cap | Free accounts | routing cost | 402 free_tier_exhausted |
| Prepaid balance | accounts using prepaid credit | your credit balance | 402 credit_exhausted |
| Your daily spend cap | accounts using prepaid credit, if you set one | your credit spend that day | 402 daily_cap |
| Your monthly spend cap | accounts using prepaid credit, if you set one | your credit spend that month | 402 monthly_cap |
| Account monthly ceiling | all paid accounts, including those using prepaid credit | our routing cost, not your charge — see below | 402 account_monthly_budget_exhausted |
| Per-key lifetime cap | any key you stamp one on | that key's cumulative spend | 402 key_lifetime_cap_exhausted |
Each of the codes above is documented, with the exact response shape, in What a 402 error means.
The basis the account ceiling is measured on
The account monthly ceiling is compared against our cost of routing your traffic, not against the amount you were charged. Those two numbers are not the same, and the gap is not small: across the accounts we measured, our routing cost was on median about 47% of the customer charge. On that ratio a $50 account ceiling first bites somewhere near $100 of billed usage rather than at $50 of billed usage.
We are stating this plainly because the honest reading matters: the account ceiling is a runaway-cost brake, not a promise that your bill stops at the ceiling number. If you need a bill that stops at a number you choose, use prepaid credit and set your own daily or monthly cap — those are measured on your credit spend directly, and they are the limits that bind on the amount you actually pay.
If your account uses prepaid credit
Prepaid accounts are bounded by their balance and by the caps they set, and those still bind first — in practice a prepaid balance is usually the tighter limit, because it stops you at money you have already decided to spend.
The account monthly ceiling now applies on top of them as well. At your account monthly ceiling the next request is refused with 402 account_monthly_budget_exhausted — on prepaid accounts as well as on accounts billed in arrears. This page previously said the ceiling was not applied to prepaid accounts, which was accurate at the time; it is enforced now.
{"ceiling_page_state": {
"finding_verdict": "MAKE IT BIND",
"finding_source": "21-FINDING.md",
"enforcement_live": true,
"as_of": "2026-08-06",
"customer_sentence": "At your account monthly ceiling the next request is refused with 402 `account_monthly_budget_exhausted` — on prepaid accounts as well as on accounts billed in arrears.",
"evidence": {
"prepaid": "22-TRIPPED.json — a prepaid credit_armed=true account driven over its published ceiling against https://api.fluxrouter.ai on 2026-08-06 was refused 402 account_monthly_budget_exhausted, with flux_account_ceiling_refusal_total incrementing.",
"arrears": "22-402-CONTRACT.json — provoked 402 account_monthly_budget_exhausted on 2026-08-04, BEFORE this enforcement was armed. Arrears was already binding; it is not a change made here."
},
"paths_enforced": [
{"limit": "free_tier_monthly_cap", "basis": "routing cost", "binds_today": true},
{"limit": "prepaid_balance", "basis": "credit balance", "binds_today": true},
{"limit": "self_set_daily_cap", "basis": "credit spend", "binds_today": true},
{"limit": "self_set_monthly_cap", "basis": "credit spend", "binds_today": true},
{"limit": "key_lifetime_cap", "basis": "key spend", "binds_today": true},
{"limit": "account_monthly_ceiling", "basis": "routing cost", "binds_today": true,
"scope": "paid accounts not using prepaid credit"},
{"limit": "account_monthly_ceiling", "basis": "routing cost", "binds_today": true,
"scope": "accounts using prepaid credit"}
]
}}
Does my ceiling go up over time?
Yes, on paid plans. Your ceiling starts modest and rises as you build a payment history — it grows with your cleared spend (usage that has been successfully paid and not disputed) and with your account age. The longer you have been a paying customer in good standing, the higher it climbs.
This mirrors how the major model providers handle usage limits: new accounts start with a conservative cap, and the cap increases automatically as the account establishes a track record. You don't need to do anything special.
Enterprise accounts are governed by their contract rather than this automatic schedule.
How do I request a higher ceiling?
For most accounts the ceiling rises automatically, so the usual path is to keep using the platform and let it grow. If you have a near-term need that exceeds your current ceiling (a launch, a batch job, a traffic spike), contact support or your account rep to discuss raising it ahead of the automatic schedule. Enterprise customers can set a custom ceiling as part of their contract.
Where do I see my current spend?
Your current spend and remaining headroom are in the dashboard. See Reading your usage and invoices.