Stripe Cannot Bill a 5 Cent API Call (Yet). These Four Builders Can.

ISSUE 02 · 8 MIN

An agent cannot fill in a signup form, so for years it could not buy an answer from anyone. Four builders now sell to agents by the call, from a tenth of a cent to $5, with no account on either side, and the ground they took was empty because the old rails could not price anything under 30 cents.

You run an API, a scraper, a model, or a dataset that answers a question somebody else needs answered, and today it sits behind a signup form, a card page, and a pricing tier that an agent cannot get through, because an agent does not fill in forms. The fix is a shelf where the price is written on the request and the payment travels in the response, so the agent asks, the endpoint quotes a price, the agent pays, and the answer comes back in one round trip with no account on either side.

Four builders run shelves like that today, on different rails and with different cuts, and between them they have settled tens of millions of calls that the old API marketplaces could not have priced at all.

The problem these builds attack is not that nobody wanted to sell an API. It is that the rails could not carry a small price. Stripe's standard rate is 2.9% plus 30 cents on every successful charge, which means a 5-cent API call costs 30.15 cents to collect, a fee of about 600% of the sale, and a 1-cent call costs thirty times what it earns. No pricing page in the world could survive that, so for fifteen years the smallest unit anyone could sell was a monthly plan, and every API that should have been priced by the answer was priced by the seat instead. The seat was not a business decision. It was the smallest thing the card networks could bill.

On top of the rail sat the marketplace, and the marketplace charged like a landlord. RapidAPI, the largest API marketplace of the last decade, kept a cut of every provider's revenue, ran for years on a $1 billion valuation, and was sold to Nokia in November 2024 for a price reported at close to a tenth of that. The digital storefronts everyone knows charge the same way: Apple takes 30% of an App Store sale, or 15% under its small business terms, Google Play takes 15%, and even AWS Marketplace, the cheap one, takes 3% of a SaaS listing. That is the terrain: a 30-cent floor on the rail and a 15 to 30% toll on the shelf, and together they made it uneconomic to sell any single answer worth less than a dollar.

The builds below run on a different rail. The x402 protocol, which puts a price and a payment address into an ordinary HTTP response, moved from almost nothing in mid 2025 to more than 100 million cumulative transactions on Base by the end of the first quarter of 2026, according to Chainalysis, and Coinbase's facilitator charges $0.001 per settled payment after the first 1,000 in a month. A tenth of a cent is a fee a 5-cent call can afford. The whole market that opens up when the floor drops from 30 cents to a tenth of a cent is the market these four builders are standing in, and the analysts who size the API marketplace business at $21.3 billion in 2025 are counting only the part that was billable on the old rails.

The incumbents are not asleep. Mastercard launched Agent Pay for Machines on 10 June 2026 to carry fractions of a cent between agents, which is a card network admitting that its 30-cent floor is the thing under attack. It has not published a fee, and until it does, the guerrilla has the price advantage on every call under a dollar.

LISTED · PAY PER CALL ROUTER

A pay-per-call router of 573 web tools, covering browser rendering, search, PDF and OCR, whois, and dossier reports, priced from $0.001 for a whois lookup to $0.55 for a dossier. Stablecoin settlement across 12 chains, plus a free proof of work tier for pure CPU tools. The site's live counter reads 32,226 settled calls. Builder Mike Petrillo.

Reach them · [email protected] · @Agent402Tools · agent402.tools

LISTED · API MARKETPLACE

Launched April 2026. Domain experts list an API, agents find it and pay per request in USDC on Base, from $0.001 to $5.00 per call. Listing is free, and the provider keeps 100%. 102 live APIs and 621 endpoints. An API earns a settlement-verified badge only after PayAPI pays for a test call and gets a response. Builder Chet Parker, a UK property data specialist working from Portugal.

Reach them · [email protected] · payapi.market

LISTED · AGENT MARKETPLACE

A marketplace for shipping an agent with its own chat window and getting paid per run. Buyers pay $0.001 to $0.50 a run or $9 to $99 one-time, through a pre-funded budget balance or pay per request on Base. Creators keep 90%, and the 10% is taken at cash out rather than per run. Builder Philippe.

Reach them · @pilvand · indie.money

LISTED · MODEL AND TOOL GATEWAY

The big one. A single OpenAI-compatible endpoint that routes to 100+ models and 183 data and tool APIs, billed at the provider's rate plus a $0.001 gateway fee, settled in USDC on Base and Solana. The site reports 28.9 million transactions settled on chain, and its open source router, ClawRouter, has 6.6k GitHub stars.

Reach them · @BlockRunAI · github.com/BlockRunAI

All four products get paid the same way. The agent's owner loads a wallet with stablecoins, the agent calls an endpoint, the endpoint replies with a price, the agent pays it from the wallet, and the answer arrives. Nobody signs up, nobody invoices anybody, and the seller never meets a customer. The four differ in the cut. PayAPI charges the provider nothing and bets that its verified badge brings the buyers. indie.money keeps 10% when a creator cashes out. BlockRun keeps a tenth of a cent on every call and bets on 28.9 million of them. Agent402 sells its own tools and keeps the full price. If you plan to sell on this shelf, read it the way a CFO would, because the numbers are small and the vocabulary matters more when they are.

Start with average revenue per call: the price you actually collect divided by the calls you actually serve, and on this shelf it runs from a tenth of a cent to about 50 cents. Against that sits cost of revenue, the cost that arrives with every call whether or not you have staff, and here it has three parts: the compute to produce the answer, the settlement fee to collect the money, and the share the marketplace keeps. On a 5-cent call settled through Coinbase's facilitator at a tenth of a cent, the settlement cost is 2% of the sale, which leaves a gross margin of 98% before compute, and that is the number that makes a 5-cent product possible at all. Put the same call on a card, and the 30-cent floor turns the gross margin negative by a factor of six, so there is no business to discuss.

The second term is take rate, the share of gross transaction value a platform keeps, and on this shelf it is the whole strategy in one number. BlockRun's tenth of a cent on a $1 call is a 0.1% take rate, which is a hundred times lower than an app store and only works at tens of millions of calls, and that is the bet the 28.9 million figure represents. indie.money's 10% at cash out is a take rate too, but it is charged on money the creator has already earned, so the platform is funding its cut from the creator's working capital rather than from each sale.

The third term is survival, which a CFO would call retention and which on this shelf is nasty. A catalog we tracked probed 13,334 pay per call endpoints and found 957 still answering, a 7.2% survival rate, so most sellers built something, listed it, and let it die. Retention on a shelf where the buyer is a machine means uptime, because an agent that gets one timeout never calls again and never tells you why. The seller who stays up is the seller who keeps the volume, and volume is the only thing a 0.1% take rate can be built on.

Pick the one endpoint you already run that a stranger's agent would pay for, and put a price on it this weekend. Half a cent a call is fine, because you are not pricing for revenue yet; you are pricing so that an agent never has to ask a human for permission to use it. List it on PayAPI Market, where listing is free and the settlement badge does your marketing, and then put a monitor on your own endpoint, because the 7.2% who survived are the ones who did that step.

In the second week, count distinct paying wallets rather than dollars, and when one wallet is 30% of your calls, that is your first account, and it has never emailed you. Price it at a tenth of a cent above what the shelf charges and you win on cost; price it at what the agent would pay a human to find the same answer and you win on margin, and the margin is the better business.

x402-foundation/x402 · Apache 2.0, 6.3k stars, 1.8k forks, with TypeScript, Python, and Go packages and Solidity contracts in one repository. This is the protocol under three of the four builds above, moved from Coinbase's own account into a foundation, so the old coinbase/x402 repo you may have bookmarked is a stale fork.

Why it is worth an hour: the specs directory is the entire protocol in a few pages, the HTTP 402 challenge and the payment header that answers it, and once you have read it you understand every marketplace in this issue. The framework packages for Express, Fastify, Next.js, and Hono put a paywall on an existing API in an afternoon without touching the protocol by hand, and the examples directory has a working seller and a working buyer you can run against Base Sepolia before a real dollar moves. What to add before you go live is a per wallet rate limit, because the protocol prices a call and does not care who is calling.

The buyers on this shelf are agents that pay whatever the last page told them to. On 2 July 2026, Zscaler ThreatLabz found a fake Python documentation page carrying instructions, hidden in the CSS, that told any agent reading it to send 0.0012 ETH, about $3, to a hardcoded wallet as an "API key fee," and the rail carried the money exactly as designed, to the wrong recipient. SecurityWeek carried it. As a seller, a buyer whose owner never authorized the spend is a dispute you cannot process on a rail with no refunds; and as a buyer, an agent with a funded wallet and no list of approved endpoints will pay the first page that asks nicely.

If you want a machine to confirm that the agent calling you was allowed to spend before you serve the answer, FLINT Scout does that for a cent, and that is the only pitch you will get from us.

NEXT ISSUE

Money you are owed: an agent that reads your inbox, files the flight claim, and takes 30% of what lands on the ground, where the incumbents take 35% plus a legal surcharge, and fewer than half of eligible passengers ever claim. Four builders, and the one that charges $4.99 a week.