Celo buy Marketplace: How AI Agents Pay in USDC, USDT and USAT

Every API an AI agent wants still asks a human for an account, a card, and a key. Celo's buy marketplace drops all three: the agent gets a price over HTTP 402, pays it in a stablecoin, and gets the result back in the same request.

Celo Core Co. switched buy on for mainnet on 13 October 2026, with 782 tools listed in the catalogue and payments in USDC, USDT or USAT, according to the Celo developer announcement. This guide covers what the Celo buy marketplace is, how a purchase settles, how to wire it into an agent step by step, what it really costs, and where it breaks.

Key Takeaways

• buy went live on Celo on 13 October 2026 with 782 listed tools.
• Agents pay per request in USDC, USDT or USAT; the gateway pays the gas.
• VM leases cost 2x Google's us-west1 list price, per public rate data.
• Always run buy quote first and set max-amount on every paid call (skill docs).
• It's pre-1.0 beta with no external audit, so fund it like a float (usebuy.ai).

x402 Protocol: How HTTP 402 Stablecoin Payments Work

Stablecoin Insider's explainer on the x402 payment flow that buy uses under the hood: the 402 challenge, the signed payment, and the facilitator.

Stablecoin Insider

What is the Celo buy marketplace?

buy is two things at once. It's a catalogue of paid HTTP services at usebuy.ai, and it's a command-line client, @celo/buy, that pays those services' 402 challenges from a wallet held in your OS keychain.

The catalogue lists 782 tools across compute, blockchain data, web data and browser sessions, with prices read from each service on 13 October 2026, according to the usebuy.ai catalogue page. The three launch partners are Cencori for LLM inference, Chainstack for archive-capable Celo RPC, and SQD for multi-chain blockchain data, per Celo's launch post.

Here's why that matters. An agent that needs a VM, a search result and an RPC read would normally need three vendor accounts. With buy it needs one funded wallet, and you need one place to set a budget.

buy also leans on Self, a zero-knowledge proof-of-human layer. Google Cloud's larger machines on buy are rented "only to agents that can present a Self proof confirming a real, verified adult is behind the request", according to Blockchain.News' report on the launch. That's the same know-your-agent problem Stablecoin Insider covered in Know Your Agent (KYA) in 2026.

How a buy purchase settles

Under the hood, buy is an x402 client. Celo's launch post describes the purchase in four steps, and Celo's x402 docs fill in the protocol details:

• Your agent calls a service URL with no payment attached.
• The service answers HTTP 402 Payment Required with a price, token, network and recipient.
• buy signs a payment for exactly that amount, locally, with the keychain wallet.
• The request is retried with the payment header, the payment settles on Celo, and the result comes back.

Two Celo features make this work for an agent that only holds dollars. First of all, the buy gateway's sponsor wallet pays gas on x402 settlements, so the buyer never needs CELO, according to the celo-org/buy-skill README. Second, when you move money out with buy send, the transaction pays its own gas in the stablecoin being sent through CIP-64, which is Celo's fee abstraction feature.

Celo's docs pitch the economics plainly: card rails charge 2-3% plus $0.30 and need a $0.50-plus minimum, while an x402 payment on Celo costs about $0.001 in gas with a $0.001 minimum, according to the Celo x402 page. If you want to accept payments rather than make them, Celo also runs a hosted facilitator at x402.celo.org, and Stablecoin Insider's x402 facilitator guide compares the options.

How to set up the Celo buy marketplace for an AI agent

You need Node.js 20 or newer. No clone, npm login or global install is required, because every command runs through npx with a pinned version. Pinning matters here: the package is beta software, and the npm registry lists 14 releases between 25 August and 13 October 2026.

Step 1: Create a dedicated wallet

Create a new wallet just for the agent. Celo mainnet is the default network, and the key lands in your OS keychain, not in a file the model can read.

npx --yes @celo/buy@0.8.3 setup --name demo
npx --yes @celo/buy@0.8.3 whoami

If you must reuse a wallet you already control, the README's import path reads the raw key from an environment variable or stdin, never from a command argument, so it doesn't land in shell history. Encrypted keystore files aren't supported.

Step 2: Fund it with a small stablecoin float

Send a small amount of USDC, USDT or USAT on Celo mainnet to the printed address. USAT is Anchorage Digital Bank's dollar token, which went live on Celo on 29 July 2026 (see Stablecoin Insider's USAT on Celo report and the USAT explainer).

The buy-skill README puts the rule bluntly: "Fund the wallet like a float, not a treasury. Nothing prompts per payment." Treat whatever you deposit as already spent, and size it to one day of expected calls.

Step 3: Quote before you pay

Run buy quote with the exact request you plan to send. It stops at the 402 and prints each offer's token, price, network, recipient and whether a Self proof is required, without a wallet and without paying. The request body sets the price, so a bigger machine or a longer browser session changes the quote.

npx --yes @celo/buy@0.8.3 quote \
  -X POST \
  --data '[{"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params":[]}]' \
  https://gateway.usebuy.ai/chainstack/celo

Step 4: Make a capped paid call

Swap quote for curl and add a hard cap. The Chainstack Celo RPC route below costs $0.01 for a batch of up to 2,000 JSON-RPC calls, according to the usebuy.ai catalogue, so a cap of 0.01 lets exactly one batch through.

npx --yes @celo/buy@0.8.3 --verbose curl \
  --max-amount 0.01 \
  -X POST \
  --data '[{"jsonrpc":"2.0","id":1,"method":"eth_blockNumber","params":[]}]' \
  https://gateway.usebuy.ai/chainstack/celo

USDC is the default token. Set the token flag to USDT or USAT to pay in either of those instead, but the payment only goes through if the server offers that token in its 402. The verbose flag goes before curl and prints the quote, the signing step and the settlement transaction on stderr.

Step 5: Give the agent the tools over MCP

One command registers buy as an MCP server for Claude Code, Codex and other supported clients. Restart the agent afterwards so it picks up the configuration.

npx --yes @celo/buy@0.8.3 mcp install --client all

The agent then sees buy_pay_quote, buy_curl, buy_balance, buy_whoami and buy_verify_status, per the buy-skill repository. The server signs in its own process, so the model never receives key material, and the one tool that moves money directly stays opt-in behind a budget or an allowlist. The repo also ships skills such as order-compute and use-api-gateway that teach the agent to quote first and recover safely.

Step 6: Add a Self proof only if you need big machines

The shared-core VM sizes (e2-micro, e2-small, e2-medium) need no proof. The e2-standard sizes do. The hosted verify command uses the gateway's Self receiver, checks age 18 or over and OFAC screening by default, and needs a real passport because mock proofs are rejected.

npx --yes @celo/buy@0.8.3 verify hosted \
  --endpoint https://usebuy.ai/self/api/verify

Step 7: Keep receipts and resolve failures

Run buy receipts with the account flag to list local payment history with settlement transactions. After a paid request that ended without a 2xx, the same command with the resolve flag asks the token contract whether the payment settled. Pipe those receipts into the same ledger you use for other agent spend; Stablecoin Insider's agent spend reconciliation guide shows the columns to keep.

What buy costs: Stablecoin Insider's VM price check

The catalogue makes one comparison easy, because buy's compute route rents plain Google Cloud e2 machines in us-west1. Stablecoin Insider lined up buy's one-hour lease prices from usebuy.ai against Google's on-demand hourly rates for the same machines in us-west1, as tracked by gcloud-compute.com, a public tracker of Compute Engine list prices, as read on 17 October 2026.

Source: usebuy.ai catalogue (prices read 13 October 2026); gcloud-compute.com e2 pages, us-west1 on-demand; multiples are Stablecoin Insider calculations.

The pattern is exact: every size costs 2.0x Google's list price, which looks like a flat doubling rather than a per-machine margin. On the smallest box that's an extra $0.0084 for the hour, based on Google's $0.0084 e2-micro rate. That premium buys no account, no card on file and gas paid by the gateway.

On the flip side, a team that already has a Google Cloud project pays half, and Google's committed-use contracts cut list prices by up to 55% for most machine types, according to Google's VM pricing page. buy wins on setup time and agent autonomy, not on unit cost.

Worked example: what one research-agent run costs

Here's a realistic job: an agent that spins up a VM for an hour, searches X 20 times, makes 10 LLM calls, reads Celo state twice and opens one browser session. Using the per-call prices on the usebuy.ai catalogue, Stablecoin Insider priced it line by line:

Source: unit prices from usebuy.ai as quoted on 13 October 2026; totals are Stablecoin Insider calculations. Run that job 100 times a day and the bill is about $24.59 a day, or $737.70 over 30 days.

That's the number to put in your float. It also shows where the money goes: search and inference are about 81% of the run, so the VM markup barely matters for this kind of agent, according to the same catalogue prices.

One more thing. The Chainstack route is the cheapest line on a per-read basis: $0.01 across a full 2,000-call batch works out to $0.000005 per call, based on Chainstack's buy listing. Batch your RPC reads, or you'll pay a cent for each single one.

buy vs other agent payment marketplaces

buy isn't the only place an agent can spend stablecoins this month. Here's how it lines up against two other named options, using each one's own announcement or a dated report.

Sources: usebuy.ai, TokenPost on Circle Agent Stack, Ankr's x402 launch post.

Circle's numbers explain why USDC is the default everywhere: USDC settled 99.3% of x402 agent-payment volume in Q2 2026, according to TokenPost's report on Circle's results. buy's twist is choice: an agent can hold USDT or USAT instead and still buy the same tool, if the seller offers it. If you're already on Circle's stack, Stablecoin Insider's Circle Agent Wallet guide and CDP SDK guide cover the alternatives.

The downside: where buy breaks

Let's start with the label on the box. The README says buy is "pre-1.0 beta software without an external security review" and "not intended for production use". Take that at face value.

• Payments are final. x402 has no refund primitive, and a 500 can mean you already paid, so a blind retry is a second payment (buy-skill README).
• Compute is capped. Leases run one hour at a time and 24 hours total, the service admits at most 100 VMs, and admission stops at $25/hour of catalogued compute (usebuy.ai limits).
• Egress is policed. A VM that sends more than 10 GB is deleted within minutes and the lease isn't refunded.
• Prices drift. The catalogue shows prices read on 13 October; the quote for your exact request is the only authoritative number.
• Identity cuts both ways. The Self proof needs a real passport, which suits a named operator but not an anonymous agent fleet.

And the 2.0x compute premium is real. For a steady workload you'll pay less renting the same e2 machine directly from Google, per Google's list rates. buy suits bursty, unattended jobs where no one wants to provision a cloud account.

That checklist is in how to test an AI agent USDC payment before going live, and per-wallet caps are covered in how to set spend limits on an AI agent USDC wallet.

Stablecoin Insider's take: the catalogue is the product

Stablecoin Insider's take: x402 clients are a commodity now. What buy adds is a priced, browsable catalogue and a gateway that hides gas, tokens and provider keys from the agent. That's the piece most agent builders were missing, and it's why buy is worth a test even with the beta label.

The bet to watch is whether sellers outside Celo's own launch partners list on it. If the catalogue keeps growing past its 782 tools and quotes stay transparent, buy becomes a default procurement layer for agents that hold dollars on Celo. If not, it stays a tidy wrapper around Google VMs at 2x list price.

Monday's move: install 0.8.3, quote three routes your agent actually needs, and fund one day of calls. For the wider market picture, the Q3 2026 stablecoin report and Stablecoin Insider's guide to stablecoin payments for AI agents put buy in context. To sell into marketplaces like this one, see how to charge AI crawlers with Agent402 Tollbooth.

Tether's USAT Stablecoin Launches on Celo

Stablecoin Insider's report on USAT's Celo deployment, one of the three stablecoins buy accepts.

Stablecoin Insider

FAQ

This content is provided for informational and educational purposes only and does not constitute financial, investment, legal, or tax advice; it is not financial advice, and no material herein should be interpreted as a recommendation, endorsement, or solicitation to buy or sell any asset or token. Package versions, catalogue prices, and gateway limits change; get a fresh quote and read the live docs before you fund a wallet. Nothing here is a solicitation to buy or sell.