The free tier at volume: what 20 free calls a day actually covers
The free tier is stated exactly: 20 free calls per day, then they upgrade. For a light caller that is a working day. For a heavy caller it is a fraction, and it pays to know the fraction cold:
| Your volume | Free calls cover | Calls past free, per day |
|---|---|---|
| 100 calls a day | 20 of 100, which is 20% | 80 |
| 200 calls a day | 20 of 200, which is 10% | 180 |
| 300 calls a day | 20 of 300, which is about 6.7% | 280 |
| 500 calls a day | 20 of 500, which is 4% | 480 |
Two ways to feel that. Across 30 days the free tier is 20 times 30, which is 600 free calls a month, every month, before any payment. And at an even pace, a 300 call day uses its 20 free calls in the first 1.6 hours of the day. The free tier does not scale with you. It was never meant to: it is the on-ramp and a permanent rebate, and the paid periods below are priced to take over from call 21.
The Pass at volume: one payment, divided by your real call count
The Zambo Pass is $29 for 30 days, one payment, on the same endpoint at zambo.dev/mcp, with a verifiable receipt on every call. Because the price is a period and not a meter, cost per call is just the payment divided by the calls you actually run in the period:
| Your volume | Calls in 30 days | Worked math | Cost per call |
|---|---|---|---|
| 100 calls a day | 100 x 30 = 3,000 | $29 / 3,000 | about $0.0097 |
| 200 calls a day | 200 x 30 = 6,000 | $29 / 6,000 | about $0.0048 |
| 300 calls a day | 300 x 30 = 9,000 | $29 / 9,000 | about $0.0032 |
| 500 calls a day | 500 x 30 = 15,000 | $29 / 15,000 | about $0.0019 |
Read the shape, not just the rows: doubling your volume halves your cost per call, because the numerator never moves. The same division prices the other periods. The holder Pass, $19 for 30 days, at 200 calls a day: $19 divided by 6,000 is about $0.0032 per call. The annual Pass, $290 for 365 days, at 200 calls a day: 200 times 365 is 73,000 calls, and $290 divided by 73,000 is about $0.0040 per call, one payment for the year. Redo the division at your own volume before you decide anything; the table is a method, not a promise about your workload.
Spike days: the $0.99 Day Pass, priced honestly
Not every heavy day deserves a 30 day commitment. A launch day, a migration, a client deadline: the Day Pass is $0.99 USDC on Base for 24 hours, 990,000 atomic units, bought by the agent itself through the x402 challenge, or by a human with PayPal or card through PayPal. On a 200 call spike day, that is $0.99 divided by 200, which is $0.00495 per call. On a 500 call spike day, $0.99 divided by 500 is $0.00198 per call. For a single day, the Day Pass beats the Pass at any volume.
The trap is the habit. A Day Pass every day for 30 days costs 30 times $0.99, which is $29.70. The Pass covers the same 30 days for $29, one payment instead of thirty, and $0.70 less. Rule of thumb: spikes on Day Passes, rhythm on the Pass. The day your spikes become your calendar, switch, and the switch pays for itself in the same month.
Receipts at volume: the record does not thin out
Heavy callers are usually the callers who most need the record, because nobody can eyeball 500 calls. On Zambo the record is per call and complete by construction: by the canonical definition, an agent receipt is a record of one ai agent tool call that anyone can check: it keeps the exact saved bytes and their sha-256 digest, and it proves the result was not changed since it was saved, not that it was right. Volume changes none of that. Calls bind into workflow records in order, a finished job closes as one checkable set, and the day reviews on zambo.dev/today.
- A closed job set at real scale: workflow close zambo.dev/run/2c970a44-fb38-49c4-9bff-1718c51a9e4b and its closing record zambo.dev/run/dff1fb91-844c-4f13-acef-82137138d7e4, each verified live before this page was written.
- A single call inside any day: a live price call, zambo.dev/run/540dac9c-9f05-4b12-9a72-94ed605c63c4, checkable free at zambo.dev/verify by whoever received the work.
That is the heavy caller bargain in one line: your per call price falls toward a fifth of a cent while your evidence trail stays at full strength, one receipt per call, at call one and at call ten thousand alike.
Which period fits your pattern
- Under 20 calls a day: stay free. You are not a heavy caller yet, and the free tier is your whole bill.
- Heavy days, light weeks: Day Passes on the heavy days only. A four spike month costs $3.96, and quiet days cost nothing.
- Heavy most days: the Pass at $29 for 30 days. Past roughly 29 heavy days in a 30 day window, near daily, the Pass becomes the cheaper shape ($29 against $29.70 in Day Passes); at one heavy day a week, Day Passes at about $3.96 to $4.24 stay far cheaper.
- Settled, year-round volume: annual at $290 for 365 days, or the holder Pass at $19 for 30 days if you hold $ZAMBO. Run the division at your volume and pick the smaller number.
Choosing the server itself on evidence, not just price? The criteria live on how to choose an MCP server with receipts. Keeping the trail for an auditor? Agent logging for compliance covers the record set end to end.
Heavy caller pricing: FAQ
My AI agent makes hundreds of calls a day. What does Zambo cost at that volume?
Work it from the two fixed prices. The free tier is 20 free calls per day, which is 600 free calls across 30 days. Past that, the Zambo Pass is $29 for 30 days, one payment. At 100 calls a day you run 3,000 calls in 30 days, so the Pass works out to $29 divided by 3,000, about $0.0097 per call. At 200 calls a day, 6,000 calls, about $0.0048 per call. At 300 calls a day, 9,000 calls, about $0.0032 per call. At 500 calls a day, 15,000 calls, about $0.0019 per call. The more you run, the cheaper each receipted call gets, because the price is one payment, not a per-call meter.
How far does the free tier go for a heavy caller?
The free tier is 20 free calls per day for every caller, heavy or light. At 100 calls a day it covers 20 percent of your day. At 200 calls a day, 10 percent. At 300 calls a day, about 6.7 percent. At 500 calls a day, 4 percent. In time terms, at an even pace across 24 hours, a 300 call day burns the free tier in roughly the first hour and a half. The free tier is a genuine start and a permanent daily rebate of 600 calls a month, but a heavy caller's real home is the Pass.
Day Pass or Zambo Pass for spike days?
A Day Pass is $0.99 for 24 hours: buy it on the spike day and that day is covered. On a 200 call spike day that is $0.99 divided by 200, $0.00495 per call. On a 500 call spike day, $0.00198 per call. But price the habit: a Day Pass every day for 30 days costs 30 times $0.99, which is $29.70, against the Pass at $29 for the same 30 days, one payment instead of thirty. Spiky weeks belong on Day Passes. Daily volume belongs on the Pass, and it is $0.70 cheaper before you count the thirty payments you did not have to make.
Do heavy callers get a receipt on every call, or only some?
Every call. Volume changes the price per call, never the record. Each call through the Zambo MCP returns its result with a verifiable AER-1 receipt, the calls of a job bind into workflow records in order, and a finished job can be closed as one checkable set. A heavy caller's day is reviewable on zambo.dev/today, and any single receipt in it can be checked free at zambo.dev/verify by the client or auditor who received the work. The receipt proves the saved result was not changed since it was saved, at call one and at call ten thousand alike.
How do agents pay for the Pass and the Day Pass?
Agents pay with USDC on Base through the x402 challenge: the Day Pass is $0.99, which is 990,000 atomic units of USDC, for 24 hours. The Zambo Pass is $29 for 30 days, one payment, with an annual option at $290 for 365 days and a holder Pass at $19 for 30 days. Humans pay by PayPal or card through PayPal on the same prices. There is no per-call meter to watch either way: one payment opens the period, and every call in it carries its receipt.
What is the cost per call for the holder Pass and the annual Pass at volume?
Same arithmetic, different numerator. The holder Pass is $19 for 30 days: at 200 calls a day, 6,000 calls in the period, $19 divided by 6,000 is about $0.0032 per call. The annual Pass is $290 for 365 days: at 200 calls a day that is 73,000 calls in the year, and $290 divided by 73,000 is about $0.0040 per call, with one payment covering the whole year. Pick the period that matches how your workload actually runs, then divide. The page you are reading shows every step so you can redo it at your own volume.