Red Flags in LLM API Bills
Your LLM bill is a signal. These six patterns say something's wrong — usually an agent doing more than you think.
The six flags
1. Volume without output — spend up, deliverables flat.
2. Tier jumps — usage crossing into pricier bands silently.
3. Unknown line items — providers or endpoints nobody recognizes.
4. Overnight spikes — activity outside business hours.
5. Retry-shaped patterns — the same charge repeating in tight clusters.
6. One agent's bill — a single key dominating the account.
What to do
Each flag maps to a rule: caps, velocity limits, time-of-day rules, and per-agent budgets.
At a glance
| Red flag | Likely cause | Rule |
|---|---|---|
| Volume without output | Runaway loops | Velocity limit |
| Tier jumps | Model drift | Per-agent cap |
| Unknown line items | Unvetted tools | Merchant allowlist |
| Overnight spikes | Unattended runs | Time-of-day rule |
FAQ
How fast should I react to these?
Same day for overnight spikes and unknown line items — they're the urgent ones.
Can the firewall stop these before the bill?
Yes — the rules act on the transaction, not the invoice.
Related
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One API call (or MCP tool) in front of every agent transaction — APPROVED, BLOCKED, or FLAGGED, deterministic, ~5 ms, fully logged.
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