Words for AI agent payments
Each entry starts with a definition you can quote, then a longer explanation, related words, and sources.
| Period | Volume | Payments | Payers | Sellers |
|---|---|---|---|---|
| 24 hours | $8,579 | 109,873 | 24,381 | 8,279 |
| 7 days | $40,132 | 186,961 | 3,727 | 2,456 |
| 30 days | $45,963 | 215,671 | 3,792 | 2,482 |
Backfill in progress on base, solana, tempo. A checkpoint is still open, so recent totals can still move.
Protocols
A2A
A2A is the Agent2Agent protocol for agents to discover each other and exchange messages. It does not settle payments.
ACP
ACP is the Agentic Commerce Protocol from OpenAI and Stripe for merchant checkout inside an agent.
AP2
AP2 is the Agentic Payment Protocol. It standardizes signed mandates that authorize an agent to check out and pay.
Bazaar
The x402 Bazaar is Coinbase CDP's public catalog of payment-gated resources and their prices.
facilitator
A facilitator verifies an x402 payment and submits the onchain settlement for a resource server.
HTTP 402
HTTP 402 Payment Required is reserved by RFC 9110. x402 and L402 both use it as a payment challenge.
L402
L402 is Lightning Labs' HTTP 402 flow: a macaroon plus a paid Lightning invoice.
Lightning
The Lightning Network moves bitcoin payments over channels. L402 uses its BOLT 11 invoices.
mandate
An AP2 mandate is a signed authorization that lets an agent complete a checkout or pay for it.
MCP
MCP is the Model Context Protocol for connecting a model to tools and data. It is not itself a payment rail.
MPP
MPP is the Machine Payments Protocol from Stripe and Tempo. Agent GDP indexes its Tempo session settlements.
payment channel
A payment channel locks a deposit and lets parties update a balance with signatures before settling onchain.
payment scheme
An x402 payment scheme is how a payment is formed and checked, such as exact, upto, or batch settlement.
PAYMENT-SIGNATURE
PAYMENT-SIGNATURE is the x402 HTTP header where the client sends its signed payment on the retry.
payTo
payTo is the x402 field that names who should receive a payment for a resource.
resource server
The x402 resource server hosts the paid URL, returns 402, and decides when to verify and settle.
shared payment token
A shared payment token is a scoped Stripe credential an agent can give a seller for one checkout.
Tempo
Tempo is the blockchain where MPP session channels settle. Mainnet is chain id 4217.
x402
x402 is an open protocol that uses HTTP 402 so a client can pay for a resource and retry the same request.
Assets and chains
Arc
Arc is Circle's layer-1 blockchain. Public mainnet launched on 16 September 2026, chain id 5042.
Base
Base is an Ethereum layer 2, chain id 8453. It is one of the x402 chains this index scans for USDC.
CAIP-2
CAIP-2 is a chain-agnostic chain id. x402 uses it in the network field, such as eip155:8453 for Base.
pathUSD
pathUSD is a Tempo quote token. This index prices it one-to-one when an MPP session settles in it.
Polygon
Polygon PoS is chain id 137. This index scans x402 USDC settlements there.
Solana
Solana is a layer-1 blockchain. This index counts x402 there when a facilitator pays the Solana fee and USDC moves.
stablecoin
A stablecoin is a token meant to track a reference asset. This index prices only the stablecoins its methodology names.
USDC
USDC is Circle's dollar stablecoin. This index prices 6-decimal USDC transfers at one dollar each.
Settlement
EIP-3009
EIP-3009 lets a token holder sign a transfer that someone else submits. x402 uses it for gasless USDC.
gas sponsorship
Gas sponsorship means someone other than the payer pays the network fee for a settlement transaction.
micropayment
A micropayment is a small payment, often below card minimums. Agent protocols use stablecoins or Lightning to make them practical.
nanopayments
Circle nanopayments are gas-free USDC payments down to one millionth of a dollar, batched through Gateway.
Permit2
Permit2 is Uniswap's contract for signature-based token approvals and transfers, including tokens without EIP-3009.
settlement
Settlement is the step that makes a payment final on the ledger the protocol uses. Agent GDP counts settlements it can read.
Wallets and identity
agent wallet
An agent wallet is the key or account an agent signs with or receives payment to. The index does not assume it is autonomous.
agentic commerce
Agentic commerce is commerce in which a software agent discovers, checks out, or pays, under constraints set by a person or a business.
AI agent
An AI agent is software that pursues a goal by calling tools. A payment counts here because of how it settled, not because the payer was labeled an agent.
ERC-4337
ERC-4337 is Ethereum account abstraction via UserOperations, bundlers, and optional gas-paying paymasters.
ERC-8004
ERC-8004 is the Ethereum standard for trustless agents: identity, reputation, and validation registries.
smart wallet
A smart wallet is an account controlled by code, often an ERC-4337 wallet. Some payment paths still require an ordinary key.
Measurement
Agent GDP
Agent GDP is the dollars AI agents paid on public records. It is not national GDP.
buyer
A buyer is the address that paid. This site also calls that address a payer. Chart bars are not the headline count.
dataset
Live and sample are separate datasets. Sample hashes are fixtures, not chain history. Pages name which one a figure came from.
organic volume
Organic volume is raw settlement that passes the seller screen: revenue, distinct buyers, a minimum average, and not a facilitator wallet.
pay-per-call
Pay-per-call means one payment for one request. It is also the default payment pattern in this index's use-case rollup.
payer
A payer is the blockchain address that sent an AI agent payment. Counts are addresses, not people.
raw volume
Raw volume is attributed settlement value before the organic seller screen. A router hop counts once.
seller
The seller is the payment recipient: x402 payTo, the USDC recipient, or the MPP payee.
settled volume
Settled volume is the dollar value of AI agent payments that finished on a public ledger.
wash trading
Wash trading is activity arranged to inflate volume. The organic screen catches some patterns and does not prove the rest is clean.
Questions
- How should a definition on this glossary be cited?
- Cite the term URL, the editorial date on the page, and the sources at the bottom. If you also cite a live figure, include the time printed next to that figure.
- Why are some protocols defined but absent from the volume?
- AP2, ACP, and L402 are real standards. They let an agent get permission to pay, check out, or pay a Lightning invoice. They do not publish one public payment record we can add up, so the definition has no dollar total beside it.